1erl_nif(3) C Library Functions erl_nif(3)
2
6 erl_nif - API functions for an Erlang NIF library.
7
9 A NIF library contains native implementation of some functions of an
10 Erlang module. The native implemented functions (NIFs) are called like
11 any other functions without any difference to the caller. A NIF library
12 is built as a dynamically linked library file and loaded in runtime by
13 calling erlang:load_nif/2.
14 Warning:
16 Use this functionality with extreme care.
18 A native function is executed as a direct extension of the native code
20 of the VM. Execution is not made in a safe environment. The VM cannot
21 provide the same services as provided when executing Erlang code, such
22 as pre-emptive scheduling or memory protection. If the native function
23 does not behave well, the whole VM will misbehave.
24 * A native function that crashes will crash the whole VM.
26 * An erroneously implemented native function can cause a VM internal
28 state inconsistency, which can cause a crash of the VM, or miscel‐
29 laneous misbehaviors of the VM at any point after the call to the
30 native function.
31 * A native function doing lengthy work before returning degrades re‐
33 sponsiveness of the VM, and can cause miscellaneous strange behav‐
34 iors. Such strange behaviors include, but are not limited to, ex‐
35 treme memory usage, and bad load balancing between schedulers.
36 Strange behaviors that can occur because of lengthy work can also
37 vary between Erlang/OTP releases.
38
40 A minimal example of a NIF library can look as follows:
41 /* niftest.c */
43 #include <erl_nif.h>
44 static ERL_NIF_TERM hello(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
46 {
47 return enif_make_string(env, "Hello world!", ERL_NIF_LATIN1);
48 }
49 static ErlNifFunc nif_funcs[] =
51 {
52 {"hello", 0, hello}
53 };
54 ERL_NIF_INIT(niftest,nif_funcs,NULL,NULL,NULL,NULL)
56 The Erlang module can look as follows:
58 -module(niftest).
60 -export([init/0, hello/0]).
62 -on_load(init/0).
64 init() ->
66 erlang:load_nif("./niftest", 0).
67 hello() ->
69 erlang:nif_error("NIF library not loaded").
70 Compile and test can look as follows (on Linux):
72 $> gcc -fPIC -shared -o niftest.so niftest.c -I $ERL_ROOT/usr/include/
74 $> erl
75 1> c(niftest).
77 {ok,niftest}
78 2> niftest:hello().
79 "Hello world!"
80 In the example above the on_load directive is used get function init
82 called automatically when the module is loaded. Function init in turn
83 calls erlang:load_nif/2 which loads the NIF library and replaces the
84 hello function with its native implementation in C. Once loaded, a NIF
85 library is persistent. It will not be unloaded until the module code
86 version that it belongs to is purged.
87 Each NIF must have an implementation in Erlang to be invoked if the
89 function is called before the NIF library is successfully loaded. A
90 typical such stub implementation is to call erlang:nif_error which will
91 raise an exception. The Erlang function can also be used as a fallback
92 implementation if the NIF library lacks implementation for some OS or
93 hardware architecture for example.
94 Note:
96 A NIF does not have to be exported, it can be local to the module. How‐
97 ever, unused local stub functions will be optimized away by the com‐
98 piler, causing loading of the NIF library to fail.
99 Warning:
102 There is a known limitation for Erlang fallback functions of NIFs.
103 Avoid functions involved in traversal of binaries by matching and re‐
104 cursion. If a NIF is loaded over such function, binary arguments to the
105 NIF may get corrupted and cause VM crash or other misbehavior.
106 Example of such bad fallback function:
108 skip_until(Byte, <<Byte, Rest/binary>>) ->
110 Rest;
111 skip_until(Byte, <<_, Rest/binary>>) ->
112 skip_until(Byte, Rest).
113
117 All interaction between NIF code and the Erlang runtime system is per‐
118 formed by calling NIF API functions. Functions exist for the following
119 functionality:
120 Read and write Erlang terms:
122 Any Erlang terms can be passed to a NIF as function arguments and
123 be returned as function return values. The terms are of C-type
124 ERL_NIF_TERM and can only be read or written using API functions.
125 Most functions to read the content of a term are prefixed enif_get_
126 and usually return true (or false) if the term is of the expected
127 type (or not). The functions to write terms are all prefixed
128 enif_make_ and usually return the created ERL_NIF_TERM. There are
129 also some functions to query terms, like enif_is_atom,
130 enif_is_identical, and enif_compare.
131 All terms of type ERL_NIF_TERM belong to an environment of type
133 ErlNifEnv. The lifetime of a term is controlled by the lifetime of
134 its environment object. All API functions that read or write terms
135 has the environment that the term belongs to as the first function
136 argument.
137 Binaries:
139 Terms of type binary are accessed with the help of struct type Erl‐
140 NifBinary, which contains a pointer (data) to the raw binary data
141 and the length (size) of the data in bytes. Both data and size are
142 read-only and are only to be written using calls to API functions.
143 Instances of ErlNifBinary are, however, always allocated by the
144 user (usually as local variables).
145 The raw data pointed to by data is only mutable after a call to
147 enif_alloc_binary or enif_realloc_binary. All other functions that
148 operate on a binary leave the data as read-only. A mutable binary
149 must in the end either be freed with enif_release_binary or made
150 read-only by transferring it to an Erlang term with enif_make_bi‐
151 nary. However, it does not have to occur in the same NIF call.
152 Read-only binaries do not have to be released.
153 enif_make_new_binary can be used as a shortcut to allocate and re‐
155 turn a binary in the same NIF call.
156 Binaries are sequences of whole bytes. Bitstrings with an arbitrary
158 bit length have no support yet.
159 Resource objects:
161 The use of resource objects is a safe way to return pointers to na‐
162 tive data structures from a NIF. A resource object is only a block
163 of memory allocated with enif_alloc_resource. A handle ("safe
164 pointer") to this memory block can then be returned to Erlang by
165 the use of enif_make_resource. The term returned by enif_make_re‐
166 source is opaque in nature. It can be stored and passed between
167 processes, but the only real end usage is to pass it back as an ar‐
168 gument to a NIF. The NIF can then call enif_get_resource and get
169 back a pointer to the memory block, which is guaranteed to still be
170 valid. A resource object is not deallocated until the last handle
171 term is garbage collected by the VM and the resource is released
172 with enif_release_resource (not necessarily in that order).
173 All resource objects are created as instances of some resource
175 type. This makes resources from different modules to be distin‐
176 guishable. A resource type is created by calling enif_open_re‐
177 source_type when a library is loaded. Objects of that resource type
178 can then later be allocated and enif_get_resource verifies that the
179 resource is of the expected type. A resource type can have a user-
180 supplied destructor function, which is automatically called when
181 resources of that type are released (by either the garbage collec‐
182 tor or enif_release_resource). Resource types are uniquely identi‐
183 fied by a supplied name string and the name of the implementing
184 module.
185 The following is a template example of how to create and return a
187 resource object.
188 ERL_NIF_TERM term;
190 MyStruct* obj = enif_alloc_resource(my_resource_type, sizeof(MyStruct));
191 /* initialize struct ... */
193 term = enif_make_resource(env, obj);
195 if (keep_a_reference_of_our_own) {
197 /* store 'obj' in static variable, private data or other resource object */
198 }
199 else {
200 enif_release_resource(obj);
201 /* resource now only owned by "Erlang" */
202 }
203 return term;
204 Notice that once enif_make_resource creates the term to return to
206 Erlang, the code can choose to either keep its own native pointer
207 to the allocated struct and release it later, or release it immedi‐
208 ately and rely only on the garbage collector to deallocate the re‐
209 source object eventually when it collects the term.
210 Another use of resource objects is to create binary terms with
212 user-defined memory management. enif_make_resource_binary creates a
213 binary term that is connected to a resource object. The destructor
214 of the resource is called when the binary is garbage collected, at
215 which time the binary data can be released. An example of this can
216 be a binary term consisting of data from a mmap'ed file. The de‐
217 structor can then do munmap to release the memory region.
218 Resource types support upgrade in runtime by allowing a loaded NIF
220 library to take over an already existing resource type and by that
221 "inherit" all existing objects of that type. The destructor of the
222 new library is thereafter called for the inherited objects and the
223 library with the old destructor function can be safely unloaded.
224 Existing resource objects, of a module that is upgraded, must ei‐
225 ther be deleted or taken over by the new NIF library. The unloading
226 of a library is postponed as long as there exist resource objects
227 with a destructor function in the library.
228 Module upgrade and static data:
230 A loaded NIF library is tied to the Erlang module instance that
231 loaded it. If the module is upgraded, the new module instance needs
232 to load its own NIF library (or maybe choose not to). The new mod‐
233 ule instance can, however, choose to load the exact same NIF li‐
234 brary as the old code if it wants to. Sharing the dynamic library
235 means that static data defined by the library is shared as well. To
236 avoid unintentionally shared static data between module instances,
237 each Erlang module version can keep its own private data. This pri‐
238 vate data can be set when the NIF library is loaded and later re‐
239 trieved by calling enif_priv_data.
240 Threads and concurrency:
242 A NIF is thread-safe without any explicit synchronization as long
243 as it acts as a pure function and only reads the supplied argu‐
244 ments. When you write to a shared state either through static vari‐
245 ables or enif_priv_data, you need to supply your own explicit syn‐
246 chronization. This includes terms in process independent environ‐
247 ments that are shared between threads. Resource objects also re‐
248 quire synchronization if you treat them as mutable.
249 The library initialization callbacks load and upgrade are thread-
251 safe even for shared state data.
252 Version Management:
254 When a NIF library is built, information about the NIF API version
255 is compiled into the library. When a NIF library is loaded, the
256 runtime system verifies that the library is of a compatible ver‐
257 sion. erl_nif.h defines the following:
258 ERL_NIF_MAJOR_VERSION:
260 Incremented when NIF library incompatible changes are made to the
261 Erlang runtime system. Normally it suffices to recompile the NIF
262 library when the ERL_NIF_MAJOR_VERSION has changed, but it can,
263 under rare circumstances, mean that NIF libraries must be
264 slightly modified. If so, this will of course be documented.
265 ERL_NIF_MINOR_VERSION:
267 Incremented when new features are added. The runtime system uses
268 the minor version to determine what features to use.
269 The runtime system normally refuses to load a NIF library if the
271 major versions differ, or if the major versions are equal and the
272 minor version used by the NIF library is greater than the one used
273 by the runtime system. Old NIF libraries with lower major versions
274 are, however, allowed after a bump of the major version during a
275 transition period of two major releases. Such old NIF libraries can
276 however fail if deprecated features are used.
277 Time Measurement:
279 Support for time measurement in NIF libraries:
280 * ErlNifTime
282 * ErlNifTimeUnit
284 * enif_monotonic_time()
286 * enif_time_offset()
288 * enif_convert_time_unit()
290 I/O Queues:
292 The Erlang nif library contains function for easily working with
293 I/O vectors as used by the unix system call writev. The I/O Queue
294 is not thread safe, so some other synchronization mechanism has to
295 be used.
296 * SysIOVec
298 * ErlNifIOVec
300 * enif_ioq_create()
302 * enif_ioq_destroy()
304 * enif_ioq_enq_binary()
306 * enif_ioq_enqv()
308 * enif_ioq_deq()
310 * enif_ioq_peek()
312 * enif_ioq_peek_head()
314 * enif_inspect_iovec()
316 * enif_free_iovec()
318 Typical usage when writing to a file descriptor looks like this:
320 int writeiovec(ErlNifEnv *env, ERL_NIF_TERM term, ERL_NIF_TERM *tail,
322 ErlNifIOQueue *q, int fd) {
323 ErlNifIOVec vec, *iovec = &vec;
325 SysIOVec *sysiovec;
326 int saved_errno;
327 int iovcnt, n;
328 if (!enif_inspect_iovec(env, 64, term, tail, &iovec))
330 return -2;
331 if (enif_ioq_size(q) > 0) {
333 /* If the I/O queue contains data we enqueue the iovec and
334 then peek the data to write out of the queue. */
335 if (!enif_ioq_enqv(q, iovec, 0))
336 return -3;
337 sysiovec = enif_ioq_peek(q, &iovcnt);
339 } else {
340 /* If the I/O queue is empty we skip the trip through it. */
341 iovcnt = iovec->iovcnt;
342 sysiovec = iovec->iov;
343 }
344 /* Attempt to write the data */
346 n = writev(fd, sysiovec, iovcnt);
347 saved_errno = errno;
348 if (enif_ioq_size(q) == 0) {
350 /* If the I/O queue was initially empty we enqueue any
351 remaining data into the queue for writing later. */
352 if (n >= 0 && !enif_ioq_enqv(q, iovec, n))
353 return -3;
354 } else {
355 /* Dequeue any data that was written from the queue. */
356 if (n > 0 && !enif_ioq_deq(q, n, NULL))
357 return -4;
358 }
359 /* return n, which is either number of bytes written or -1 if
361 some error happened */
362 errno = saved_errno;
363 return n;
364 }
365 Long-running NIFs:
367 As mentioned in the warning text at the beginning of this manual
368 page, it is of vital importance that a native function returns rel‐
369 atively fast. It is difficult to give an exact maximum amount of
370 time that a native function is allowed to work, but usually a well-
371 behaving native function is to return to its caller within 1 mil‐
372 lisecond. This can be achieved using different approaches. If you
373 have full control over the code to execute in the native function,
374 the best approach is to divide the work into multiple chunks of
375 work and call the native function multiple times. This is, however,
376 not always possible, for example when calling third-party li‐
377 braries.
378 The enif_consume_timeslice() function can be used to inform the
380 runtime system about the length of the NIF call. It is typically
381 always to be used unless the NIF executes very fast.
382 If the NIF call is too lengthy, this must be handled in one of the
384 following ways to avoid degraded responsiveness, scheduler load
385 balancing problems, and other strange behaviors:
386 Yielding NIF:
388 If the functionality of a long-running NIF can be split so that
389 its work can be achieved through a series of shorter NIF calls,
390 the application has two options:
391 * Make that series of NIF calls from the Erlang level.
393 * Call a NIF that first performs a chunk of the work, then in‐
395 vokes the enif_schedule_nif function to schedule another NIF
396 call to perform the next chunk. The final call scheduled in
397 this manner can then return the overall result.
398 Breaking up a long-running function in this manner enables the VM
400 to regain control between calls to the NIFs.
401 This approach is always preferred over the other alternatives de‐
403 scribed below. This both from a performance perspective and a
404 system characteristics perspective.
405 Threaded NIF:
407 This is accomplished by dispatching the work to another thread
408 managed by the NIF library, return from the NIF, and wait for the
409 result. The thread can send the result back to the Erlang process
410 using enif_send. Information about thread primitives is provided
411 below.
412 Dirty NIF:
414 Note:
417 Dirty NIF support is available only when the emulator is configured
418 with dirty scheduler support. As of ERTS version 9.0, dirty sched‐
419 uler support is enabled by default on the runtime system with SMP
420 support. The Erlang runtime without SMP support does not support
421 dirty schedulers even when the dirty scheduler support is explic‐
422 itly enabled. To check at runtime for the presence of dirty sched‐
423 uler threads, code can use the enif_system_info() API function.
424 A NIF that cannot be split and cannot execute in a millisecond or
427 less is called a "dirty NIF", as it performs work that the ordi‐
428 nary schedulers of the Erlang runtime system cannot handle
429 cleanly. Applications that make use of such functions must indi‐
430 cate to the runtime that the functions are dirty so they can be
431 handled specially. This is handled by executing dirty jobs on a
432 separate set of schedulers called dirty schedulers. A dirty NIF
433 executing on a dirty scheduler does not have the same duration
434 restriction as a normal NIF.
435 It is important to classify the dirty job correct. An I/O bound
437 job should be classified as such, and a CPU bound job should be
438 classified as such. If you should classify CPU bound jobs as I/O
439 bound jobs, dirty I/O schedulers might starve ordinary sched‐
440 ulers. I/O bound jobs are expected to either block waiting for
441 I/O, and/or spend a limited amount of time moving data.
442 To schedule a dirty NIF for execution, the application has two
444 options:
445 * Set the appropriate flags value for the dirty NIF in its Erl‐
447 NifFunc entry.
448 * Call enif_schedule_nif, pass to it a pointer to the dirty NIF
450 to be executed, and indicate with argument flags whether it ex‐
451 pects the operation to be CPU-bound or I/O-bound.
452 A job that alternates between I/O bound and CPU bound can be re‐
454 classified and rescheduled using enif_schedule_nif so that it ex‐
455 ecutes on the correct type of dirty scheduler at all times. For
456 more information see the documentation of the erl(1) command line
457 arguments +SDcpu, and +SDio.
458 While a process executes a dirty NIF, some operations that commu‐
460 nicate with it can take a very long time to complete. Suspend or
461 garbage collection of a process executing a dirty NIF cannot be
462 done until the dirty NIF has returned. Thus, other processes
463 waiting for such operations to complete might have to wait for a
464 very long time. Blocking multi-scheduling, that is, calling er‐
465 lang:system_flag(multi_scheduling, block), can also take a very
466 long time to complete. This is because all ongoing dirty opera‐
467 tions on all dirty schedulers must complete before the block op‐
468 eration can complete.
469 Many operations communicating with a process executing a dirty
471 NIF can, however, complete while it executes the dirty NIF. For
472 example, retrieving information about it through process_info,
473 setting its group leader, register/unregister its name, and so
474 on.
475 Termination of a process executing a dirty NIF can only be com‐
477 pleted up to a certain point while it executes the dirty NIF. All
478 Erlang resources, such as its registered name and its ETS tables,
479 are released. All links and monitors are triggered. The execution
480 of the NIF is, however, not stopped. The NIF can safely continue
481 execution, allocate heap memory, and so on, but it is of course
482 better to stop executing as soon as possible. The NIF can check
483 whether a current process is alive using enif_is_cur‐
484 rent_process_alive. Communication using enif_send and
485 enif_port_command is also dropped when the sending process is not
486 alive. Deallocation of certain internal resources, such as
487 process heap and process control block, is delayed until the
488 dirty NIF has completed.
489
491 ERL_NIF_INIT(MODULE, ErlNifFunc funcs[], load, NULL, upgrade, un‐
492 load):
493 This is the magic macro to initialize a NIF library. It is to be
494 evaluated in global file scope.
495 MODULE is the name of the Erlang module as an identifier without
497 string quotations. It is stringified by the macro.
498 funcs is a static array of function descriptors for all the imple‐
500 mented NIFs in this library.
501 load, upgrade and unload are pointers to functions. One of load or
503 upgrade is called to initialize the library. unload is called to
504 release the library. All are described individually below.
505 The fourth argument NULL is ignored. It was earlier used for the
507 deprecated reload callback which is no longer supported since OTP
508 20.
509 If compiling a NIF for static inclusion through --enable-static-
511 nifs, you must define STATIC_ERLANG_NIF before the ERL_NIF_INIT
512 declaration.
513 int (*load)(ErlNifEnv* caller_env, void** priv_data, ERL_NIF_TERM
515 load_info):
516 load is called when the NIF library is loaded and no previously
517 loaded library exists for this module.
518 *priv_data can be set to point to some private data if the library
520 needs to keep a state between NIF calls. enif_priv_data returns
521 this pointer. *priv_data is initialized to NULL when load is
522 called.
523 load_info is the second argument to erlang:load_nif/2.
525 The library fails to load if load returns anything other than 0.
527 load can be NULL if initialization is not needed.
528 int (*upgrade)(ErlNifEnv* caller_env, void** priv_data, void**
530 old_priv_data, ERL_NIF_TERM load_info):
531 upgrade is called when the NIF library is loaded and there is old
532 code of this module with a loaded NIF library.
533 Works as load, except that *old_priv_data already contains the
535 value set by the last call to load or upgrade for the old module
536 code. *priv_data is initialized to NULL when upgrade is called. It
537 is allowed to write to both *priv_data and *old_priv_data.
538 The library fails to load if upgrade returns anything other than 0
540 or if upgrade is NULL.
541 void (*unload)(ErlNifEnv* caller_env, void* priv_data):
543 unload is called when the module code that the NIF library belongs
544 to is purged as old. New code of the same module may or may not ex‐
545 ist.
546
548 ERL_NIF_TERM:
549 Variables of type ERL_NIF_TERM can refer to any Erlang term. This
550 is an opaque type and values of it can only by used either as argu‐
551 ments to API functions or as return values from NIFs. All
552 ERL_NIF_TERMs belong to an environment (ErlNifEnv). A term cannot
553 be destructed individually, it is valid until its environment is
554 destructed.
555 ErlNifEnv:
557 ErlNifEnv represents an environment that can host Erlang terms. All
558 terms in an environment are valid as long as the environment is
559 valid. ErlNifEnv is an opaque type; pointers to it can only be
560 passed on to API functions. Three types of environments exist:
561 Process bound environment:
563 Passed as the first argument to all NIFs. All function arguments
564 passed to a NIF belong to that environment. The return value from
565 a NIF must also be a term belonging to the same environment.
566 A process bound environment contains transient information about
568 the calling Erlang process. The environment is only valid in the
569 thread where it was supplied as argument until the NIF returns.
570 It is thus useless and dangerous to store pointers to process
571 bound environments between NIF calls.
572 Callback environment:
574 Passed as the first argument to all the non-NIF callback func‐
575 tions (load, upgrade, unload, dtor, down and stop). Works like a
576 process bound environment but with a temporary pseudo process
577 that "terminates" when the callback has returned. Terms may be
578 created in this environment but they will only be accessible dur‐
579 ing the callback.
580 Process independent environment:
582 Created by calling enif_alloc_env. This environment can be used
583 to store terms between NIF calls and to send terms with
584 enif_send. A process independent environment with all its terms
585 is valid until you explicitly invalidate it with enif_free_env or
586 enif_send.
587 All contained terms of a list/tuple/map must belong to the same en‐
589 vironment as the list/tuple/map itself. Terms can be copied between
590 environments with enif_make_copy.
591 ErlNifFunc:
593 typedef struct {
596 const char* name;
597 unsigned arity;
598 ERL_NIF_TERM (*fptr)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]);
599 unsigned flags;
600 } ErlNifFunc;
601 Describes a NIF by its name, arity, and implementation.
603 fptr:
605 A pointer to the function that implements the NIF.
606 argv:
608 Contains the function arguments passed to the NIF.
609 argc:
611 The array length, that is, the function arity. argv[N-1] thus de‐
612 notes the Nth argument to the NIF. Notice that the argument argc
613 allows for the same C function to implement several Erlang func‐
614 tions with different arity (but probably with the same name).
615 flags:
617 Is 0 for a regular NIF (and so its value can be omitted for stat‐
618 ically initialized ErlNifFunc instances).
619 flags can be used to indicate that the NIF is a dirty NIF that is
621 to be executed on a dirty scheduler thread.
622 If the dirty NIF is expected to be CPU-bound, its flags field is
624 to be set to ERL_NIF_DIRTY_JOB_CPU_BOUND or
625 ERL_NIF_DIRTY_JOB_IO_BOUND.
626 Note:
628 If one of the ERL_NIF_DIRTY_JOB_*_BOUND flags is set, and the run‐
629 time system has no support for dirty schedulers, the runtime system
630 refuses to load the NIF library.
631 ErlNifBinary:
634 typedef struct {
637 size_t size;
638 unsigned char* data;
639 } ErlNifBinary;
640 ErlNifBinary contains transient information about an inspected bi‐
642 nary term. data is a pointer to a buffer of size bytes with the raw
643 content of the binary.
644 Notice that ErlNifBinary is a semi-opaque type and you are only al‐
646 lowed to read fields size and data.
647 ErlNifBinaryToTerm:
649 An enumeration of the options that can be specified to enif_bi‐
650 nary_to_term. For default behavior, use value 0.
651 When receiving data from untrusted sources, use option
653 ERL_NIF_BIN2TERM_SAFE.
654 ErlNifMonitor:
656 This is an opaque data type that identifies a monitor.
657 The nif writer is to provide the memory for storing the monitor
659 when calling enif_monitor_process. The address of the data is not
660 stored by the runtime system, so ErlNifMonitor can be used as any
661 other data, it can be copied, moved in memory, forgotten, and so
662 on. To compare two monitors, enif_compare_monitors must be used.
663 ErlNifPid:
665 A process identifier (pid). In contrast to pid terms (instances of
666 ERL_NIF_TERM), ErlNifPids are self-contained and not bound to any
667 environment. ErlNifPid is an opaque type. It can be copied, moved
668 in memory, forgotten, and so on.
669 ErlNifPort:
671 A port identifier. In contrast to port ID terms (instances of
672 ERL_NIF_TERM), ErlNifPorts are self-contained and not bound to any
673 environment. ErlNifPort is an opaque type. It can be copied, moved
674 in memory, forgotten, and so on.
675 ErlNifResourceType:
677 Each instance of ErlNifResourceType represents a class of memory-
678 managed resource objects that can be garbage collected. Each re‐
679 source type has a unique name and a destructor function that is
680 called when objects of its type are released.
681 ErlNifResourceTypeInit:
683 typedef struct {
686 ErlNifResourceDtor* dtor;
687 ErlNifResourceStop* stop;
688 ErlNifResourceDown* down;
689 } ErlNifResourceTypeInit;
690 Initialization structure read by enif_open_resource_type_x.
692 ErlNifResourceDtor:
694 typedef void ErlNifResourceDtor(ErlNifEnv* caller_env, void* obj);
697 The function prototype of a resource destructor function.
699 The obj argument is a pointer to the resource. The only allowed use
701 for the resource in the destructor is to access its user data one
702 final time. The destructor is guaranteed to be the last callback
703 before the resource is deallocated.
704 ErlNifResourceDown:
706 typedef void ErlNifResourceDown(ErlNifEnv* caller_env, void* obj, ErlNifPid* pid, ErlNifMonitor* mon);
709 The function prototype of a resource down function, called on the
711 behalf of enif_monitor_process. obj is the resource, pid is the
712 identity of the monitored process that is exiting, and mon is the
713 identity of the monitor.
714 ErlNifResourceStop:
716 typedef void ErlNifResourceStop(ErlNifEnv* caller_env, void* obj, ErlNifEvent event, int is_direct_call);
719 The function prototype of a resource stop function, called on the
721 behalf of enif_select. obj is the resource, event is OS event,
722 is_direct_call is true if the call is made directly from enif_se‐
723 lect or false if it is a scheduled call (potentially from another
724 thread).
725 ErlNifCharEncoding:
727 typedef enum {
730 ERL_NIF_LATIN1
731 }ErlNifCharEncoding;
732 The character encoding used in strings and atoms. The only sup‐
734 ported encoding is ERL_NIF_LATIN1 for ISO Latin-1 (8-bit ASCII).
735 ErlNifSysInfo:
737 Used by enif_system_info to return information about the runtime
738 system. Contains the same content as ErlDrvSysInfo.
739 ErlNifSInt64:
741 A native signed 64-bit integer type.
742 ErlNifUInt64:
744 A native unsigned 64-bit integer type.
745 ErlNifTime:
747 A signed 64-bit integer type for representation of time.
748 ErlNifTimeUnit:
750 An enumeration of time units supported by the NIF API:
751 ERL_NIF_SEC:
753 Seconds
754 ERL_NIF_MSEC:
756 Milliseconds
757 ERL_NIF_USEC:
759 Microseconds
760 ERL_NIF_NSEC:
762 Nanoseconds
763 ErlNifUniqueInteger:
765 An enumeration of the properties that can be requested from
766 enif_make_unique_integer. For default properties, use value 0.
767 ERL_NIF_UNIQUE_POSITIVE:
769 Return only positive integers.
770 ERL_NIF_UNIQUE_MONOTONIC:
772 Return only strictly monotonically increasing integer corre‐
773 sponding to creation time.
774 ErlNifHash:
776 An enumeration of the supported hash types that can be generated
777 using enif_hash.
778 ERL_NIF_INTERNAL_HASH:
780 Non-portable hash function that only guarantees the same hash for
781 the same term within one Erlang VM instance.
782 It takes 32-bit salt values and generates hashes within
784 0..2^32-1.
785 ERL_NIF_PHASH2:
787 Portable hash function that gives the same hash for the same Er‐
788 lang term regardless of machine architecture and ERTS version.
789 It ignores salt values and generates hashes within 0..2^27-1.
791 Slower than ERL_NIF_INTERNAL_HASH. It corresponds to er‐
793 lang:phash2/1.
794 SysIOVec:
796 A system I/O vector, as used by writev on Unix and WSASend on
797 Win32. It is used in ErlNifIOVec and by enif_ioq_peek.
798 ErlNifIOVec:
800 typedef struct {
803 int iovcnt;
804 size_t size;
805 SysIOVec* iov;
806 } ErlNifIOVec;
807 An I/O vector containing iovcnt SysIOVecs pointing to the data. It
809 is used by enif_inspect_iovec and enif_ioq_enqv.
810 ErlNifIOQueueOpts:
812 Options to configure a ErlNifIOQueue.
813 ERL_NIF_IOQ_NORMAL:
815 Create a normal I/O Queue
816
818 void *enif_alloc(size_t size)
819 Allocates memory of size bytes.
821 Returns NULL if the allocation fails.
823 The returned pointer is suitably aligned for any built-in type
825 that fit in the allocated memory.
826 int enif_alloc_binary(size_t size, ErlNifBinary* bin)
828 Allocates a new binary of size size bytes. Initializes the
830 structure pointed to by bin to refer to the allocated binary.
831 The binary must either be released by enif_release_binary or
832 ownership transferred to an Erlang term with enif_make_binary.
833 An allocated (and owned) ErlNifBinary can be kept between NIF
834 calls.
835 If you do not need to reallocate or keep the data alive across
837 NIF calls, consider using enif_make_new_binary instead as it
838 will allocate small binaries on the process heap when possible.
839 Returns true on success, or false if allocation fails.
841 ErlNifEnv *enif_alloc_env()
843 Allocates a new process independent environment. The environment
845 can be used to hold terms that are not bound to any process.
846 Such terms can later be copied to a process environment with
847 enif_make_copy or be sent to a process as a message with
848 enif_send.
849 Returns pointer to the new environment.
851 void *enif_alloc_resource(ErlNifResourceType*
853 type, unsigned size)
854 Allocates a memory-managed resource object of type type and size
856 size bytes.
857 size_t enif_binary_to_term(ErlNifEnv *env,
859 const unsigned char* data, size_t size, ERL_NIF_TERM *term,
860 ErlNifBinaryToTerm opts)
861 Creates a term that is the result of decoding the binary data at
863 data, which must be encoded according to the Erlang external
864 term format. No more than size bytes are read from data. Argu‐
865 ment opts corresponds to the second argument to erlang:bi‐
866 nary_to_term/2 and must be either 0 or ERL_NIF_BIN2TERM_SAFE.
867 On success, stores the resulting term at *term and returns the
869 number of bytes read. Returns 0 if decoding fails or if opts is
870 invalid.
871 See also ErlNifBinaryToTerm, erlang:binary_to_term/2, and
873 enif_term_to_binary.
874 void enif_clear_env(ErlNifEnv* env)
876 Frees all terms in an environment and clears it for reuse. The
878 environment must have been allocated with enif_alloc_env.
879 int enif_compare(ERL_NIF_TERM lhs, ERL_NIF_TERM rhs)
881 Returns an integer < 0 if lhs < rhs, 0 if lhs = rhs, and > 0 if
883 lhs > rhs. Corresponds to the Erlang operators ==, /=, =<, <,
884 >=, and > (but not =:= or =/=).
885 int enif_compare_monitors(const ErlNifMonitor
887 *monitor1, const ErlNifMonitor *monitor2)
888 Compares two ErlNifMonitors. Can also be used to imply some ar‐
890 tificial order on monitors, for whatever reason.
891 Returns 0 if monitor1 and monitor2 are equal, < 0 if monitor1 <
893 monitor2, and > 0 if monitor1 > monitor2.
894 int enif_compare_pids(const ErlNifPid *pid1, const ErlNifPid *pid2)
896 Compares two ErlNifPids according to term order.
899 Returns 0 if pid1 and pid2 are equal, < 0 if pid1 < pid2, and >
901 0 if pid1 > pid2.
902 void enif_cond_broadcast(ErlNifCond *cnd)
904 Same as erl_drv_cond_broadcast.
906 ErlNifCond *enif_cond_create(char *name)
908 Same as erl_drv_cond_create.
910 void enif_cond_destroy(ErlNifCond *cnd)
912 Same as erl_drv_cond_destroy.
914 char*enif_cond_name(ErlNifCond* cnd)
916 Same as erl_drv_cond_name.
918 void enif_cond_signal(ErlNifCond *cnd)
920 Same as erl_drv_cond_signal.
922 void enif_cond_wait(ErlNifCond *cnd, ErlNifMutex *mtx)
924 Same as erl_drv_cond_wait.
926 int enif_consume_timeslice(ErlNifEnv *env, int percent)
928 Gives the runtime system a hint about how much CPU time the cur‐
930 rent NIF call has consumed since the last hint, or since the
931 start of the NIF if no previous hint has been specified. The
932 time is specified as a percent of the timeslice that a process
933 is allowed to execute Erlang code until it can be suspended to
934 give time for other runnable processes. The scheduling timeslice
935 is not an exact entity, but can usually be approximated to about
936 1 millisecond.
937 Notice that it is up to the runtime system to determine if and
939 how to use this information. Implementations on some platforms
940 can use other means to determine consumed CPU time. Lengthy NIFs
941 should regardless of this frequently call enif_consume_timeslice
942 to determine if it is allowed to continue execution.
943 Argument percent must be an integer between 1 and 100. This
945 function must only be called from a NIF-calling thread, and ar‐
946 gument env must be the environment of the calling process.
947 Returns 1 if the timeslice is exhausted, otherwise 0. If 1 is
949 returned, the NIF is to return as soon as possible in order for
950 the process to yield.
951 This function is provided to better support co-operative sched‐
953 uling, improve system responsiveness, and make it easier to pre‐
954 vent misbehaviors of the VM because of a NIF monopolizing a
955 scheduler thread. It can be used to divide length work into a
956 number of repeated NIF calls without the need to create threads.
957 See also the warning text at the beginning of this manual page.
959 ErlNifTime enif_convert_time_unit(ErlNifTime
961 val, ErlNifTimeUnit from, ErlNifTimeUnit to)
962 Converts the val value of time unit from to the corresponding
964 value of time unit to. The result is rounded using the floor
965 function.
966 val:
968 Value to convert time unit for.
969 from:
971 Time unit of val.
972 to:
974 Time unit of returned value.
975 Returns ERL_NIF_TIME_ERROR if called with an invalid time unit
977 argument.
978 See also ErlNifTime and ErlNifTimeUnit.
980 ERL_NIF_TERM enif_cpu_time(ErlNifEnv *)
982 Returns the CPU time in the same format as erlang:timestamp().
984 The CPU time is the time the current logical CPU has spent exe‐
985 cuting since some arbitrary point in the past. If the OS does
986 not support fetching this value, enif_cpu_time invokes
987 enif_make_badarg.
988 int enif_demonitor_process(ErlNifEnv* caller_env,
990 void* obj, const ErlNifMonitor* mon)
991 Cancels a monitor created earlier with enif_monitor_process. Ar‐
993 gument obj is a pointer to the resource holding the monitor and
994 *mon identifies the monitor.
995 Argument caller_env is the environment of the calling thread
997 (process bound or callback environment) or NULL if calling from
998 a custom thread not spawned by ERTS.
999 Returns 0 if the monitor was successfully identified and re‐
1001 moved. Returns a non-zero value if the monitor could not be
1002 identified, which means it was either
1003 * never created for this resource
1005 * already cancelled
1007 * already triggered
1009 * just about to be triggered by a concurrent thread
1011 This function is only thread-safe when the emulator with SMP
1013 support is used. It can only be used in a non-SMP emulator from
1014 a NIF-calling thread.
1015 int enif_equal_tids(ErlNifTid tid1, ErlNifTid tid2)
1017 Same as erl_drv_equal_tids.
1019 int enif_fprintf(FILE *stream, const char *format, ...)
1021 Similar to fprintf but this format string also accepts "%T",
1023 which formats Erlang terms of type ERL_NIF_TERM.
1024 This function is primarily intended for debugging purpose. It is
1026 not recommended to print very large terms with %T. The function
1027 may change errno, even if successful.
1028 void enif_free(void* ptr)
1030 Frees memory allocated by enif_alloc.
1032 void enif_free_env(ErlNifEnv* env)
1034 Frees an environment allocated with enif_alloc_env. All terms
1036 created in the environment are freed as well.
1037 void enif_free_iovec(ErlNifIOVec* iov)
1039 Frees an io vector returned from enif_inspect_iovec. This is
1041 needed only if a NULL environment is passed to enif_in‐
1042 spect_iovec.
1043 ErlNifIOVec *iovec = NULL;
1045 size_t max_elements = 128;
1046 ERL_NIF_TERM tail;
1047 if (!enif_inspect_iovec(NULL, max_elements, term, &tail, &iovec))
1048 return 0;
1049 // Do things with the iovec
1051 /* Free the iovector, possibly in another thread or nif function call */
1053 enif_free_iovec(iovec);
1054 int enif_get_atom(ErlNifEnv* env, ERL_NIF_TERM
1056 term, char* buf, unsigned size, ErlNifCharEncoding encode)
1057 Writes a NULL-terminated string in the buffer pointed to by buf
1059 of size size, consisting of the string representation of the
1060 atom term with encoding encode.
1061 Returns the number of bytes written (including terminating NULL
1063 character) or 0 if term is not an atom with maximum length of
1064 size-1.
1065 int enif_get_atom_length(ErlNifEnv* env,
1067 ERL_NIF_TERM term, unsigned* len, ErlNifCharEncoding encode)
1068 Sets *len to the length (number of bytes excluding terminating
1070 NULL character) of the atom term with encoding encode.
1071 Returns true on success, or false if term is not an atom.
1073 int enif_get_double(ErlNifEnv* env,
1075 ERL_NIF_TERM term, double* dp)
1076 Sets *dp to the floating-point value of term.
1078 Returns true on success, or false if term is not a float.
1080 int enif_get_int(ErlNifEnv* env, ERL_NIF_TERM
1082 term, int* ip)
1083 Sets *ip to the integer value of term.
1085 Returns true on success, or false if term is not an integer or
1087 is outside the bounds of type int.
1088 int enif_get_int64(ErlNifEnv* env, ERL_NIF_TERM
1090 term, ErlNifSInt64* ip)
1091 Sets *ip to the integer value of term.
1093 Returns true on success, or false if term is not an integer or
1095 is outside the bounds of a signed 64-bit integer.
1096 int enif_get_local_pid(ErlNifEnv* env,
1098 ERL_NIF_TERM term, ErlNifPid* pid)
1099 If term is the pid of a node local process, this function ini‐
1101 tializes the pid variable *pid from it and returns true. Other‐
1102 wise returns false. No check is done to see if the process is
1103 alive.
1104 Note:
1106 enif_get_local_pid will return false if argument term is the
1107 atom undefined.
1108 int enif_get_local_port(ErlNifEnv* env,
1111 ERL_NIF_TERM term, ErlNifPort* port_id)
1112 If term identifies a node local port, this function initializes
1114 the port variable *port_id from it and returns true. Otherwise
1115 returns false. No check is done to see if the port is alive.
1116 int enif_get_list_cell(ErlNifEnv* env,
1118 ERL_NIF_TERM list, ERL_NIF_TERM* head, ERL_NIF_TERM* tail)
1119 Sets *head and *tail from list list.
1121 Returns true on success, or false if it is not a list or the
1123 list is empty.
1124 int enif_get_list_length(ErlNifEnv* env,
1126 ERL_NIF_TERM term, unsigned* len)
1127 Sets *len to the length of list term.
1129 Returns true on success, or false if term is not a proper list.
1131 int enif_get_long(ErlNifEnv* env, ERL_NIF_TERM
1133 term, long int* ip)
1134 Sets *ip to the long integer value of term.
1136 Returns true on success, or false if term is not an integer or
1138 is outside the bounds of type long int.
1139 int enif_get_map_size(ErlNifEnv* env,
1141 ERL_NIF_TERM term, size_t *size)
1142 Sets *size to the number of key-value pairs in the map term.
1144 Returns true on success, or false if term is not a map.
1146 int enif_get_map_value(ErlNifEnv* env,
1148 ERL_NIF_TERM map, ERL_NIF_TERM key, ERL_NIF_TERM* value)
1149 Sets *value to the value associated with key in the map map.
1151 Returns true on success, or false if map is not a map or if map
1153 does not contain key.
1154 int enif_get_resource(ErlNifEnv* env,
1156 ERL_NIF_TERM term, ErlNifResourceType* type, void** objp)
1157 Sets *objp to point to the resource object referred to by term.
1159 Returns true on success, or false if term is not a handle to a
1161 resource object of type type.
1162 enif_get_resource does not add a reference to the resource ob‐
1164 ject. However, the pointer received in *objp is guaranteed to be
1165 valid at least as long as the resource handle term is valid.
1166 int enif_get_string(ErlNifEnv* env,
1168 ERL_NIF_TERM list, char* buf, unsigned size,
1169 ErlNifCharEncoding encode)
1170 Writes a NULL-terminated string in the buffer pointed to by buf
1172 with size size, consisting of the characters in the string list.
1173 The characters are written using encoding encode.
1174 Returns one of the following:
1176 * The number of bytes written (including terminating NULL
1178 character)
1179 * -size if the string was truncated because of buffer space
1181 * 0 if list is not a string that can be encoded with encode or
1183 if size was < 1.
1184 The written string is always NULL-terminated, unless buffer size
1186 is < 1.
1187 int enif_get_tuple(ErlNifEnv* env, ERL_NIF_TERM
1189 term, int* arity, const ERL_NIF_TERM** array)
1190 If term is a tuple, this function sets *array to point to an ar‐
1192 ray containing the elements of the tuple, and sets *arity to the
1193 number of elements. Notice that the array is read-only and (*ar‐
1194 ray)[N-1] is the Nth element of the tuple. *array is undefined
1195 if the arity of the tuple is zero.
1196 Returns true on success, or false if term is not a tuple.
1198 int enif_get_uint(ErlNifEnv* env, ERL_NIF_TERM
1200 term, unsigned int* ip)
1201 Sets *ip to the unsigned integer value of term.
1203 Returns true on success, or false if term is not an unsigned in‐
1205 teger or is outside the bounds of type unsigned int.
1206 int enif_get_uint64(ErlNifEnv* env,
1208 ERL_NIF_TERM term, ErlNifUInt64* ip)
1209 Sets *ip to the unsigned integer value of term.
1211 Returns true on success, or false if term is not an unsigned in‐
1213 teger or is outside the bounds of an unsigned 64-bit integer.
1214 int enif_get_ulong(ErlNifEnv* env, ERL_NIF_TERM
1216 term, unsigned long* ip)
1217 Sets *ip to the unsigned long integer value of term.
1219 Returns true on success, or false if term is not an unsigned in‐
1221 teger or is outside the bounds of type unsigned long.
1222 int enif_getenv(const char* key, char* value,
1224 size_t *value_size)
1225 Same as erl_drv_getenv.
1227 int enif_has_pending_exception(ErlNifEnv* env,
1229 ERL_NIF_TERM* reason)
1230 Returns true if a pending exception is associated with the envi‐
1232 ronment env. If reason is a NULL pointer, ignore it. Otherwise,
1233 if a pending exception associated with env exists, set *reason
1234 to the value of the exception term. For example, if
1235 enif_make_badarg is called to set a pending badarg exception, a
1236 later call to enif_has_pending_exception(env, &reason) sets
1237 *reason to the atom badarg, then return true.
1238 See also enif_make_badarg and enif_raise_exception.
1240 ErlNifUInt64 enif_hash(ErlNifHash type, ERL_NIF_TERM term, ErlNifUInt64
1242 salt)
1243 Hashes term according to the specified ErlNifHash type.
1245 Ranges of taken salt (if any) and returned value depend on the
1247 hash type.
1248 int enif_inspect_binary(ErlNifEnv* env,
1250 ERL_NIF_TERM bin_term, ErlNifBinary* bin)
1251 Initializes the structure pointed to by bin with information
1253 about binary term bin_term.
1254 Returns true on success, or false if bin_term is not a binary.
1256 int enif_inspect_iolist_as_binary(ErlNifEnv*
1258 env, ERL_NIF_TERM term, ErlNifBinary* bin)
1259 Initializes the structure pointed to by bin with a continuous
1261 buffer with the same byte content as iolist. As with inspect_bi‐
1262 nary, the data pointed to by bin is transient and does not need
1263 to be released.
1264 Returns true on success, or false if iolist is not an iolist.
1266 int enif_inspect_iovec(ErlNifEnv*
1268 env, size_t max_elements, ERL_NIF_TERM iovec_term,
1269 ERL_NIF_TERM* tail,
1270 ErlNifIOVec** iovec)
1271 Fills iovec with the list of binaries provided in iovec_term.
1273 The number of elements handled in the call is limited to max_el‐
1274 ements, and tail is set to the remainder of the list. Note that
1275 the output may be longer than max_elements on some platforms.
1276 To create a list of binaries from an arbitrary iolist, use er‐
1278 lang:iolist_to_iovec/1.
1279 When calling this function, iovec should contain a pointer to
1281 NULL or a ErlNifIOVec structure that should be used if possible.
1282 e.g.
1283 /* Don't use a pre-allocated structure */
1285 ErlNifIOVec *iovec = NULL;
1286 enif_inspect_iovec(env, max_elements, term, &tail, &iovec);
1287 /* Use a stack-allocated vector as an optimization for vectors with few elements */
1289 ErlNifIOVec vec, *iovec = &vec;
1290 enif_inspect_iovec(env, max_elements, term, &tail, &iovec);
1291 The contents of the iovec is valid until the called nif function
1294 returns. If the iovec should be valid after the nif call re‐
1295 turns, it is possible to call this function with a NULL environ‐
1296 ment. If no environment is given the iovec owns the data in the
1297 vector and it has to be explicitly freed using enif_free_iovec.
1298 Returns true on success, or false if iovec_term not an iovec.
1300 ErlNifIOQueue *enif_ioq_create(ErlNifIOQueueOpts opts)
1302 Create a new I/O Queue that can be used to store data. opts has
1304 to be set to ERL_NIF_IOQ_NORMAL.
1305 void enif_ioq_destroy(ErlNifIOQueue *q)
1307 Destroy the I/O queue and free all of it's contents
1309 int enif_ioq_deq(ErlNifIOQueue *q, size_t count, size_t *size)
1311 Dequeue count bytes from the I/O queue. If size is not NULL, the
1313 new size of the queue is placed there.
1314 Returns true on success, or false if the I/O does not contain
1316 count bytes. On failure the queue is left un-altered.
1317 int enif_ioq_enq_binary(ErlNifIOQueue *q, ErlNifBinary *bin, size_t
1319 skip)
1320 Enqueue the bin into q skipping the first skip bytes.
1322 Returns true on success, or false if skip is greater than the
1324 size of bin. Any ownership of the binary data is transferred to
1325 the queue and bin is to be considered read-only for the rest of
1326 the NIF call and then as released.
1327 int enif_ioq_enqv(ErlNifIOQueue *q, ErlNifIOVec *iovec, size_t skip)
1329 Enqueue the iovec into q skipping the first skip bytes.
1331 Returns true on success, or false if skip is greater than the
1333 size of iovec.
1334 SysIOVec *enif_ioq_peek(ErlNifIOQueue *q, int *iovlen)
1336 Get the I/O queue as a pointer to an array of SysIOVecs. It also
1338 returns the number of elements in iovlen.
1339 Nothing is removed from the queue by this function, that must be
1341 done with enif_ioq_deq.
1342 The returned array is suitable to use with the Unix system call
1344 writev.
1345 int enif_ioq_peek_head(ErlNifEnv *env, ErlNifIOQueue *q, size_t *size,
1347 ERL_NIF_TERM *bin_term)
1348 Get the head of the IO Queue as a binary term.
1350 If size is not NULL, the size of the head is placed there.
1352 Nothing is removed from the queue by this function, that must be
1354 done with enif_ioq_deq.
1355 Returns true on success, or false if the queue is empty.
1357 size_t enif_ioq_size(ErlNifIOQueue *q)
1359 Get the size of q.
1361 int enif_is_atom(ErlNifEnv* env, ERL_NIF_TERM term)
1363 Returns true if term is an atom.
1365 int enif_is_binary(ErlNifEnv* env, ERL_NIF_TERM term)
1367 Returns true if term is a binary.
1369 int enif_is_current_process_alive(ErlNifEnv* env)
1371 Returns true if the currently executing process is currently
1373 alive, otherwise false.
1374 This function can only be used from a NIF-calling thread, and
1376 with an environment corresponding to currently executing pro‐
1377 cesses.
1378 int enif_is_empty_list(ErlNifEnv* env,
1380 ERL_NIF_TERM term)
1381 Returns true if term is an empty list.
1383 int enif_is_exception(ErlNifEnv* env,
1385 ERL_NIF_TERM term)
1386 Return true if term is an exception.
1388 int enif_is_fun(ErlNifEnv* env, ERL_NIF_TERM
1390 term)
1391 Returns true if term is a fun.
1393 int enif_is_identical(ERL_NIF_TERM lhs,
1395 ERL_NIF_TERM rhs)
1396 Returns true if the two terms are identical. Corresponds to the
1398 Erlang operators =:= and =/=.
1399 int enif_is_list(ErlNifEnv* env, ERL_NIF_TERM term)
1401 Returns true if term is a list.
1403 int enif_is_map(ErlNifEnv* env, ERL_NIF_TERM
1405 term)
1406 Returns true if term is a map, otherwise false.
1408 int enif_is_number(ErlNifEnv* env, ERL_NIF_TERM
1410 term)
1411 Returns true if term is a number.
1413 int enif_is_pid(ErlNifEnv* env, ERL_NIF_TERM term)
1415 Returns true if term is a pid.
1417 int enif_is_pid_undefined(const ErlNifPid* pid)
1419 Returns true if pid has been set as undefined by
1421 enif_set_pid_undefined.
1422 int enif_is_port(ErlNifEnv* env, ERL_NIF_TERM term)
1424 Returns true if term is a port.
1426 int enif_is_port_alive(ErlNifEnv* env,
1428 ErlNifPort *port_id)
1429 Returns true if port_id is alive.
1431 This function is only thread-safe when the emulator with SMP
1433 support is used. It can only be used in a non-SMP emulator from
1434 a NIF-calling thread.
1435 int enif_is_process_alive(ErlNifEnv* env,
1437 ErlNifPid *pid)
1438 Returns true if pid is alive.
1440 This function is only thread-safe when the emulator with SMP
1442 support is used. It can only be used in a non-SMP emulator from
1443 a NIF-calling thread.
1444 int enif_is_ref(ErlNifEnv* env, ERL_NIF_TERM term)
1446 Returns true if term is a reference.
1448 int enif_is_tuple(ErlNifEnv* env, ERL_NIF_TERM term)
1450 Returns true if term is a tuple.
1452 int enif_keep_resource(void* obj)
1454 Adds a reference to resource object obj obtained from enif_al‐
1456 loc_resource. Each call to enif_keep_resource for an object must
1457 be balanced by a call to enif_release_resource before the object
1458 is destructed.
1459 ERL_NIF_TERM enif_make_atom(ErlNifEnv* env, const char* name)
1461 Creates an atom term from the NULL-terminated C-string name with
1463 ISO Latin-1 encoding. If the length of name exceeds the maximum
1464 length allowed for an atom (255 characters), enif_make_atom in‐
1465 vokes enif_make_badarg.
1466 ERL_NIF_TERM enif_make_atom_len(ErlNifEnv* env,
1468 const char* name, size_t len)
1469 Create an atom term from the string name with length len. NULL
1471 characters are treated as any other characters. If len exceeds
1472 the maximum length allowed for an atom (255 characters),
1473 enif_make_atom invokes enif_make_badarg.
1474 ERL_NIF_TERM enif_make_badarg(ErlNifEnv* env)
1476 Makes a badarg exception to be returned from a NIF, and asso‐
1478 ciates it with environment env. Once a NIF or any function it
1479 calls invokes enif_make_badarg, the runtime ensures that a
1480 badarg exception is raised when the NIF returns, even if the NIF
1481 attempts to return a non-exception term instead.
1482 The return value from enif_make_badarg can be used only as the
1484 return value from the NIF that invoked it (directly or indi‐
1485 rectly) or be passed to enif_is_exception, but not to any other
1486 NIF API function.
1487 See also enif_has_pending_exception and enif_raise_exception.
1489 Note:
1491 Before ERTS 7.0 (Erlang/OTP 18), the return value from
1492 enif_make_badarg had to be returned from the NIF. This require‐
1493 ment is now lifted as the return value from the NIF is ignored
1494 if enif_make_badarg has been invoked.
1495 ERL_NIF_TERM enif_make_binary(ErlNifEnv* env, ErlNifBinary* bin)
1498 Makes a binary term from bin. Any ownership of the binary data
1500 is transferred to the created term and bin is to be considered
1501 read-only for the rest of the NIF call and then as released.
1502 ERL_NIF_TERM enif_make_copy(ErlNifEnv* dst_env,
1504 ERL_NIF_TERM src_term)
1505 Makes a copy of term src_term. The copy is created in environ‐
1507 ment dst_env. The source term can be located in any environment.
1508 ERL_NIF_TERM enif_make_double(ErlNifEnv* env, double d)
1510 Creates a floating-point term from a double. If argument double
1512 is not finite or is NaN, enif_make_double invokes
1513 enif_make_badarg.
1514 int enif_make_existing_atom(ErlNifEnv* env,
1516 const char* name, ERL_NIF_TERM* atom, ErlNifCharEncoding
1517 encode)
1518 Tries to create the term of an already existing atom from the
1520 NULL-terminated C-string name with encoding encode.
1521 If the atom already exists, this function stores the term in
1523 *atom and returns true, otherwise false. Also returns false if
1524 the length of name exceeds the maximum length allowed for an
1525 atom (255 characters).
1526 int enif_make_existing_atom_len(ErlNifEnv* env,
1528 const char* name, size_t len, ERL_NIF_TERM* atom, ErlNifCharEn‐
1529 coding
1530 encoding)
1531 Tries to create the term of an already existing atom from the
1533 string name with length len and encoding encode. NULL characters
1534 are treated as any other characters.
1535 If the atom already exists, this function stores the term in
1537 *atom and returns true, otherwise false. Also returns false if
1538 len exceeds the maximum length allowed for an atom (255 charac‐
1539 ters).
1540 ERL_NIF_TERM enif_make_int(ErlNifEnv* env, int i)
1542 Creates an integer term.
1544 ERL_NIF_TERM enif_make_int64(ErlNifEnv* env, ErlNifSInt64 i)
1546 Creates an integer term from a signed 64-bit integer.
1548 ERL_NIF_TERM enif_make_list(ErlNifEnv* env, unsigned cnt, ...)
1550 Creates an ordinary list term of length cnt. Expects cnt number
1552 of arguments (after cnt) of type ERL_NIF_TERM as the elements of
1553 the list.
1554 Returns an empty list if cnt is 0.
1556 ERL_NIF_TERM enif_make_list1(ErlNifEnv* env, ERL_NIF_TERM e1)
1558 ERL_NIF_TERM enif_make_list2(ErlNifEnv* env,
1559 ERL_NIF_TERM e1, ERL_NIF_TERM e2)
1560 ERL_NIF_TERM enif_make_list3(ErlNifEnv* env,
1561 ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3)
1562 ERL_NIF_TERM enif_make_list4(ErlNifEnv* env,
1563 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4)
1564 ERL_NIF_TERM enif_make_list5(ErlNifEnv* env,
1565 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5)
1566 ERL_NIF_TERM enif_make_list6(ErlNifEnv* env,
1567 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6)
1568 ERL_NIF_TERM enif_make_list7(ErlNifEnv* env,
1569 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7)
1570 ERL_NIF_TERM enif_make_list8(ErlNifEnv* env,
1571 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8)
1572 ERL_NIF_TERM enif_make_list9(ErlNifEnv* env,
1573 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9)
1574 Creates an ordinary list term with length indicated by the func‐
1576 tion name. Prefer these functions (macros) over the variadic
1577 enif_make_list to get a compile-time error if the number of ar‐
1578 guments does not match.
1579 ERL_NIF_TERM enif_make_list_cell(ErlNifEnv*
1581 env, ERL_NIF_TERM head, ERL_NIF_TERM tail)
1582 Creates a list cell [head | tail].
1584 ERL_NIF_TERM enif_make_list_from_array(ErlNifEnv* env, const
1586 ERL_NIF_TERM
1587 arr[], unsigned cnt)
1588 Creates an ordinary list containing the elements of array arr of
1590 length cnt.
1591 Returns an empty list if cnt is 0.
1593 ERL_NIF_TERM enif_make_long(ErlNifEnv* env, long int i)
1595 Creates an integer term from a long int.
1597 int enif_make_map_put(ErlNifEnv* env,
1599 ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM value,
1600 ERL_NIF_TERM* map_out)
1601 Makes a copy of map map_in and inserts key with value. If key
1603 already exists in map_in, the old associated value is replaced
1604 by value.
1605 If successful, this function sets *map_out to the new map and
1607 returns true. Returns false if map_in is not a map.
1608 The map_in term must belong to environment env.
1610 int enif_make_map_remove(ErlNifEnv* env,
1612 ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM* map_out)
1613 If map map_in contains key, this function makes a copy of map_in
1615 in *map_out, and removes key and the associated value. If map
1616 map_in does not contain key, *map_out is set to map_in.
1617 Returns true on success, or false if map_in is not a map.
1619 The map_in term must belong to environment env.
1621 int enif_make_map_update(ErlNifEnv* env,
1623 ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM new_value,
1624 ERL_NIF_TERM* map_out)
1625 Makes a copy of map map_in and replace the old associated value
1627 for key with new_value.
1628 If successful, this function sets *map_out to the new map and
1630 returns true. Returns false if map_in is not a map or if it does
1631 not contain key.
1632 The map_in term must belong to environment env.
1634 int enif_make_map_from_arrays(ErlNifEnv* env, ERL_NIF_TERM keys[],
1636 ERL_NIF_TERM values[], size_t cnt, ERL_NIF_TERM *map_out)
1637 Makes a map term from the given keys and values.
1639 If successful, this function sets *map_out to the new map and
1641 returns true. Returns false there are any duplicate keys.
1642 All keys and values must belong to env.
1644 ERL_NIF_TERM enif_make_monitor_term(ErlNifEnv* env, const ErlNifMoni‐
1646 tor* mon)
1647 Creates a term identifying the given monitor received from
1649 enif_monitor_process.
1650 This function is primarily intended for debugging purpose.
1652 unsigned char *enif_make_new_binary(ErlNifEnv*
1654 env, size_t size, ERL_NIF_TERM* termp)
1655 Allocates a binary of size size bytes and creates an owning
1657 term. The binary data is mutable until the calling NIF returns.
1658 This is a quick way to create a new binary without having to use
1659 ErlNifBinary. The drawbacks are that the binary cannot be kept
1660 between NIF calls and it cannot be reallocated.
1661 Returns a pointer to the raw binary data and sets *termp to the
1663 binary term.
1664 ERL_NIF_TERM enif_make_new_map(ErlNifEnv* env)
1666 Makes an empty map term.
1668 ERL_NIF_TERM enif_make_pid(ErlNifEnv* env, const ErlNifPid* pid)
1670 Makes a pid term or the atom undefined from *pid.
1672 ERL_NIF_TERM enif_make_ref(ErlNifEnv* env)
1674 Creates a reference like erlang:make_ref/0.
1676 ERL_NIF_TERM enif_make_resource(ErlNifEnv* env, void* obj)
1678 Creates an opaque handle to a memory-managed resource object ob‐
1680 tained by enif_alloc_resource. No ownership transfer is done, as
1681 the resource object still needs to be released by enif_re‐
1682 lease_resource. However, notice that the call to enif_re‐
1683 lease_resource can occur immediately after obtaining the term
1684 from enif_make_resource, in which case the resource object is
1685 deallocated when the term is garbage collected. For more de‐
1686 tails, see the example of creating and returning a resource ob‐
1687 ject in the User's Guide.
1688 Note:
1690 Since ERTS 9.0 (OTP-20.0), resource terms have a defined behav‐
1691 ior when compared and serialized through term_to_binary or
1692 passed between nodes.
1693 * Two resource terms will compare equal if and only if they
1695 would yield the same resource object pointer when passed to
1696 enif_get_resource.
1697 * A resource term can be serialized with term_to_binary and
1699 later be fully recreated if the resource object is still
1700 alive when binary_to_term is called. A stale resource term
1701 will be returned from binary_to_term if the resource object
1702 has been deallocated. enif_get_resource will return false
1703 for stale resource terms.
1704 The same principles of serialization apply when passing re‐
1706 source terms in messages to remote nodes and back again. A
1707 resource term will act stale on all nodes except the node
1708 where its resource object is still alive in memory.
1709 Before ERTS 9.0 (OTP-20.0), all resource terms did compare equal
1711 to each other and to empty binaries (<<>>). If serialized, they
1712 would be recreated as plain empty binaries.
1713 ERL_NIF_TERM enif_make_resource_binary(ErlNifEnv* env, void* obj, const
1716 void* data, size_t size)
1717 Creates a binary term that is memory-managed by a resource ob‐
1719 ject obj obtained by enif_alloc_resource. The returned binary
1720 term consists of size bytes pointed to by data. This raw binary
1721 data must be kept readable and unchanged until the destructor of
1722 the resource is called. The binary data can be stored external
1723 to the resource object, in which case the destructor is respon‐
1724 sible for releasing the data.
1725 Several binary terms can be managed by the same resource object.
1727 The destructor is not called until the last binary is garbage
1728 collected. This can be useful to return different parts of a
1729 larger binary buffer.
1730 As with enif_make_resource, no ownership transfer is done. The
1732 resource still needs to be released with enif_release_resource.
1733 int enif_make_reverse_list(ErlNifEnv* env, ERL_NIF_TERM list_in,
1735 ERL_NIF_TERM *list_out)
1736 Sets *list_out to the reverse list of the list list_in and re‐
1738 turns true, or returns false if list_in is not a list.
1739 This function is only to be used on short lists, as a copy is
1741 created of the list, which is not released until after the NIF
1742 returns.
1743 The list_in term must belong to environment env.
1745 ERL_NIF_TERM enif_make_string(ErlNifEnv* env,
1747 const char* string, ErlNifCharEncoding encoding)
1748 Creates a list containing the characters of the NULL-terminated
1750 string string with encoding encoding.
1751 ERL_NIF_TERM enif_make_string_len(ErlNifEnv*
1753 env, const char* string, size_t len, ErlNifCharEncoding
1754 encoding)
1755 Creates a list containing the characters of the string string
1757 with length len and encoding encoding. NULL characters are
1758 treated as any other characters.
1759 ERL_NIF_TERM enif_make_sub_binary(ErlNifEnv*
1761 env, ERL_NIF_TERM bin_term, size_t pos, size_t size)
1762 Makes a subbinary of binary bin_term, starting at zero-based po‐
1764 sition pos with a length of size bytes. bin_term must be a bi‐
1765 nary or bitstring. pos+size must be less or equal to the number
1766 of whole bytes in bin_term.
1767 ERL_NIF_TERM enif_make_tuple(ErlNifEnv* env,
1769 unsigned cnt, ...)
1770 Creates a tuple term of arity cnt. Expects cnt number of argu‐
1772 ments (after cnt) of type ERL_NIF_TERM as the elements of the
1773 tuple.
1774 ERL_NIF_TERM enif_make_tuple1(ErlNifEnv* env,
1776 ERL_NIF_TERM e1)
1777 ERL_NIF_TERM enif_make_tuple2(ErlNifEnv* env,
1778 ERL_NIF_TERM e1, ERL_NIF_TERM e2)
1779 ERL_NIF_TERM enif_make_tuple3(ErlNifEnv* env,
1780 ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3)
1781 ERL_NIF_TERM enif_make_tuple4(ErlNifEnv* env,
1782 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4)
1783 ERL_NIF_TERM enif_make_tuple5(ErlNifEnv* env,
1784 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5)
1785 ERL_NIF_TERM enif_make_tuple6(ErlNifEnv* env,
1786 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6)
1787 ERL_NIF_TERM enif_make_tuple7(ErlNifEnv* env,
1788 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7)
1789 ERL_NIF_TERM enif_make_tuple8(ErlNifEnv* env,
1790 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8)
1791 ERL_NIF_TERM enif_make_tuple9(ErlNifEnv* env,
1792 ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9)
1793 Creates a tuple term with length indicated by the function name.
1795 Prefer these functions (macros) over the variadic enif_make_tu‐
1796 ple to get a compile-time error if the number of arguments does
1797 not match.
1798 ERL_NIF_TERM enif_make_tuple_from_array(ErlNifEnv* env, const
1800 ERL_NIF_TERM
1801 arr[], unsigned cnt)
1802 Creates a tuple containing the elements of array arr of length
1804 cnt.
1805 ERL_NIF_TERM enif_make_uint(ErlNifEnv* env, unsigned int i)
1807 Creates an integer term from an unsigned int.
1809 ERL_NIF_TERM enif_make_uint64(ErlNifEnv* env, ErlNifUInt64 i)
1811 Creates an integer term from an unsigned 64-bit integer.
1813 ERL_NIF_TERM enif_make_ulong(ErlNifEnv* env, unsigned long i)
1815 Creates an integer term from an unsigned long int.
1817 ERL_NIF_TERM enif_make_unique_integer(ErlNifEnv
1819 *env, ErlNifUniqueInteger properties)
1820 Returns a unique integer with the same properties as specified
1822 by erlang:unique_integer/1.
1823 env is the environment to create the integer in.
1825 ERL_NIF_UNIQUE_POSITIVE and ERL_NIF_UNIQUE_MONOTONIC can be
1827 passed as the second argument to change the properties of the
1828 integer returned. They can be combined by OR:ing the two values
1829 together.
1830 See also ErlNifUniqueInteger.
1832 int enif_map_iterator_create(ErlNifEnv *env,
1834 ERL_NIF_TERM map, ErlNifMapIterator *iter, ErlNifMapIteratorEn‐
1835 try
1836 entry)
1837 Creates an iterator for the map map by initializing the struc‐
1839 ture pointed to by iter. Argument entry determines the start po‐
1840 sition of the iterator: ERL_NIF_MAP_ITERATOR_FIRST or
1841 ERL_NIF_MAP_ITERATOR_LAST.
1842 Returns true on success, or false if map is not a map.
1844 A map iterator is only useful during the lifetime of environment
1846 env that the map belongs to. The iterator must be destroyed by
1847 calling enif_map_iterator_destroy:
1848 ERL_NIF_TERM key, value;
1850 ErlNifMapIterator iter;
1851 enif_map_iterator_create(env, my_map, &iter, ERL_NIF_MAP_ITERATOR_FIRST);
1852 while (enif_map_iterator_get_pair(env, &iter, &key, &value)) {
1854 do_something(key,value);
1855 enif_map_iterator_next(env, &iter);
1856 }
1857 enif_map_iterator_destroy(env, &iter);
1858 Note:
1860 The key-value pairs of a map have no defined iteration order.
1861 The only guarantee is that the iteration order of a single map
1862 instance is preserved during the lifetime of the environment
1863 that the map belongs to.
1864 void enif_map_iterator_destroy(ErlNifEnv *env,
1867 ErlNifMapIterator *iter)
1868 Destroys a map iterator created by enif_map_iterator_create.
1870 int enif_map_iterator_get_pair(ErlNifEnv *env,
1872 ErlNifMapIterator *iter, ERL_NIF_TERM *key, ERL_NIF_TERM
1873 *value)
1874 Gets key and value terms at the current map iterator position.
1876 On success, sets *key and *value and returns true. Returns false
1878 if the iterator is positioned at head (before first entry) or
1879 tail (beyond last entry).
1880 int enif_map_iterator_is_head(ErlNifEnv *env,
1882 ErlNifMapIterator *iter)
1883 Returns true if map iterator iter is positioned before the first
1885 entry.
1886 int enif_map_iterator_is_tail(ErlNifEnv *env,
1888 ErlNifMapIterator *iter)
1889 Returns true if map iterator iter is positioned after the last
1891 entry.
1892 int enif_map_iterator_next(ErlNifEnv *env,
1894 ErlNifMapIterator *iter)
1895 Increments map iterator to point to the next key-value entry.
1897 Returns true if the iterator is now positioned at a valid key-
1899 value entry, or false if the iterator is positioned at the tail
1900 (beyond the last entry).
1901 int enif_map_iterator_prev(ErlNifEnv *env,
1903 ErlNifMapIterator *iter)
1904 Decrements map iterator to point to the previous key-value en‐
1906 try.
1907 Returns true if the iterator is now positioned at a valid key-
1909 value entry, or false if the iterator is positioned at the head
1910 (before the first entry).
1911 int enif_monitor_process(ErlNifEnv* caller_env,
1913 void* obj, const ErlNifPid* target_pid, ErlNifMonitor* mon)
1914 Starts monitoring a process from a resource. When a process is
1916 monitored, a process exit results in a call to the provided down
1917 callback associated with the resource type.
1918 Argument obj is pointer to the resource to hold the monitor and
1920 *target_pid identifies the local process to be monitored.
1921 If mon is not NULL, a successful call stores the identity of the
1923 monitor in the ErlNifMonitor struct pointed to by mon. This
1924 identifier is used to refer to the monitor for later removal
1925 with enif_demonitor_process or compare with enif_compare_moni‐
1926 tors. A monitor is automatically removed when it triggers or
1927 when the resource is deallocated.
1928 Argument caller_env is the environment of the calling thread
1930 (process bound or callback environment) or NULL if calling from
1931 a custom thread not spawned by ERTS.
1932 Returns 0 on success, < 0 if no down callback is provided, and >
1934 0 if the process is no longer alive or if target_pid is unde‐
1935 fined.
1936 This function is only thread-safe when the emulator with SMP
1938 support is used. It can only be used in a non-SMP emulator from
1939 a NIF-calling thread.
1940 ErlNifTime enif_monotonic_time(ErlNifTimeUnit time_unit)
1942 Returns the current Erlang monotonic time. Notice that it is
1944 not uncommon with negative values.
1945 time_unit is the time unit of the returned value.
1947 Returns ERL_NIF_TIME_ERROR if called with an invalid time unit
1949 argument, or if called from a thread that is not a scheduler
1950 thread.
1951 See also ErlNifTime and ErlNifTimeUnit.
1953 ErlNifMutex *enif_mutex_create(char *name)
1955 Same as erl_drv_mutex_create.
1957 void enif_mutex_destroy(ErlNifMutex *mtx)
1959 Same as erl_drv_mutex_destroy.
1961 void enif_mutex_lock(ErlNifMutex *mtx)
1963 Same as erl_drv_mutex_lock.
1965 char*enif_mutex_name(ErlNifMutex* mtx)
1967 Same as erl_drv_mutex_name.
1969 int enif_mutex_trylock(ErlNifMutex *mtx)
1971 Same as erl_drv_mutex_trylock.
1973 void enif_mutex_unlock(ErlNifMutex *mtx)
1975 Same as erl_drv_mutex_unlock.
1977 ERL_NIF_TERM enif_now_time(ErlNifEnv *env)
1979 Returns an erlang:now() time stamp.
1981 This function is deprecated.
1983 ErlNifResourceType *enif_open_resource_type(ErlNifEnv* env, const char*
1985 module_str, const char* name, ErlNifResourceDtor* dtor,
1986 ErlNifResourceFlags flags, ErlNifResourceFlags* tried)
1987 Creates or takes over a resource type identified by the string
1989 name and gives it the destructor function pointed to by dtor.
1990 Argument flags can have the following values:
1991 ERL_NIF_RT_CREATE:
1993 Creates a new resource type that does not already exist.
1994 ERL_NIF_RT_TAKEOVER:
1996 Opens an existing resource type and takes over ownership of
1997 all its instances. The supplied destructor dtor is called
1998 both for existing instances and new instances not yet cre‐
1999 ated by the calling NIF library.
2000 The two flag values can be combined with bitwise OR. The re‐
2002 source type name is local to the calling module. Argument mod‐
2003 ule_str is not (yet) used and must be NULL. dtor can be NULL if
2004 no destructor is needed.
2005 On success, the function returns a pointer to the resource type
2007 and *tried is set to either ERL_NIF_RT_CREATE or
2008 ERL_NIF_RT_TAKEOVER to indicate what was done. On failure, re‐
2009 turns NULL and sets *tried to flags. It is allowed to set tried
2010 to NULL.
2011 Notice that enif_open_resource_type is only allowed to be called
2013 in the two callbacks load and upgrade.
2014 See also enif_open_resource_type_x.
2016 ErlNifResourceType *enif_open_resource_type_x(ErlNifEnv* env, const
2018 char* name, const ErlNifResourceTypeInit* init,
2019 ErlNifResourceFlags flags, ErlNifResourceFlags* tried)
2020 Same as enif_open_resource_type except it accepts additional
2022 callback functions for resource types that are used together
2023 with enif_select and enif_monitor_process.
2024 Argument init is a pointer to an ErlNifResourceTypeInit struc‐
2026 ture that contains the function pointers for destructor, down
2027 and stop callbacks for the resource type.
2028 int enif_port_command(ErlNifEnv* env, const
2030 ErlNifPort* to_port, ErlNifEnv *msg_env, ERL_NIF_TERM msg)
2031 Works as erlang:port_command/2, except that it is always com‐
2033 pletely asynchronous.
2034 env:
2036 The environment of the calling process. Must not be NULL.
2037 *to_port:
2039 The port ID of the receiving port. The port ID is to refer
2040 to a port on the local node.
2041 msg_env:
2043 The environment of the message term. Can be a process inde‐
2044 pendent environment allocated with enif_alloc_env or NULL.
2045 msg:
2047 The message term to send. The same limitations apply as on
2048 the payload to erlang:port_command/2.
2049 Using a msg_env of NULL is an optimization, which groups to‐
2051 gether calls to enif_alloc_env, enif_make_copy, enif_port_com‐
2052 mand, and enif_free_env into one call. This optimization is only
2053 useful when a majority of the terms are to be copied from env to
2054 msg_env.
2055 Returns true if the command is successfully sent. Returns false
2057 if the command fails, for example:
2058 * *to_port does not refer to a local port.
2060 * The currently executing process (that is, the sender) is not
2062 alive.
2063 * msg is invalid.
2065 See also enif_get_local_port.
2067 void *enif_priv_data(ErlNifEnv* env)
2069 Returns the pointer to the private data that was set by load or
2071 upgrade.
2072 ERL_NIF_TERM enif_raise_exception(ErlNifEnv*
2074 env, ERL_NIF_TERM reason)
2075 Creates an error exception with the term reason to be returned
2077 from a NIF, and associates it with environment env. Once a NIF
2078 or any function it calls invokes enif_raise_exception, the run‐
2079 time ensures that the exception it creates is raised when the
2080 NIF returns, even if the NIF attempts to return a non-exception
2081 term instead.
2082 The return value from enif_raise_exception can only be used as
2084 the return value from the NIF that invoked it (directly or indi‐
2085 rectly) or be passed to enif_is_exception, but not to any other
2086 NIF API function.
2087 See also enif_has_pending_exception and enif_make_badarg.
2089 void *enif_realloc(void* ptr, size_t size)
2091 Reallocates memory allocated by enif_alloc to size bytes.
2093 Returns NULL if the reallocation fails.
2095 The returned pointer is suitably aligned for any built-in type
2097 that fit in the allocated memory.
2098 int enif_realloc_binary(ErlNifBinary* bin, size_t size)
2100 Changes the size of a binary bin. The source binary can be read-
2102 only, in which case it is left untouched and a mutable copy is
2103 allocated and assigned to *bin.
2104 Returns true on success, or false if memory allocation failed.
2106 void enif_release_binary(ErlNifBinary* bin)
2108 Releases a binary obtained from enif_alloc_binary.
2110 void enif_release_resource(void* obj)
2112 Removes a reference to resource object obj obtained from
2114 enif_alloc_resource. The resource object is destructed when the
2115 last reference is removed. Each call to enif_release_resource
2116 must correspond to a previous call to enif_alloc_resource or
2117 enif_keep_resource. References made by enif_make_resource can
2118 only be removed by the garbage collector.
2119 There are no guarantees exactly when the destructor of an unref‐
2121 erenced resource is called. It could be called directly by
2122 enif_release_resource but it could also be scheduled to be
2123 called at a later time possibly by another thread.
2124 ErlNifRWLock *enif_rwlock_create(char *name)
2126 Same as erl_drv_rwlock_create.
2128 void enif_rwlock_destroy(ErlNifRWLock *rwlck)
2130 Same as erl_drv_rwlock_destroy.
2132 char*enif_rwlock_name(ErlNifRWLock* rwlck)
2134 Same as erl_drv_rwlock_name.
2136 void enif_rwlock_rlock(ErlNifRWLock *rwlck)
2138 Same as erl_drv_rwlock_rlock.
2140 void enif_rwlock_runlock(ErlNifRWLock *rwlck)
2142 Same as erl_drv_rwlock_runlock.
2144 void enif_rwlock_rwlock(ErlNifRWLock *rwlck)
2146 Same as erl_drv_rwlock_rwlock.
2148 void enif_rwlock_rwunlock(ErlNifRWLock *rwlck)
2150 Same as erl_drv_rwlock_rwunlock.
2152 int enif_rwlock_tryrlock(ErlNifRWLock *rwlck)
2154 Same as erl_drv_rwlock_tryrlock.
2156 int enif_rwlock_tryrwlock(ErlNifRWLock *rwlck)
2158 Same as erl_drv_rwlock_tryrwlock.
2160 ERL_NIF_TERM enif_schedule_nif(ErlNifEnv* env,
2162 const char* fun_name, int flags, ERL_NIF_TERM (*fp)(ErlNifEnv*
2163 env, int
2164 argc, const ERL_NIF_TERM argv[]), int argc, const ERL_NIF_TERM
2165 argv[])
2166 Schedules NIF fp to execute. This function allows an application
2168 to break up long-running work into multiple regular NIF calls or
2169 to schedule a dirty NIF to execute on a dirty scheduler thread.
2170 fun_name:
2172 Provides a name for the NIF that is scheduled for execution.
2173 If it cannot be converted to an atom, enif_schedule_nif re‐
2174 turns a badarg exception.
2175 flags:
2177 Must be set to 0 for a regular NIF. If the emulator was
2178 built with dirty scheduler support enabled, flags can be set
2179 to either ERL_NIF_DIRTY_JOB_CPU_BOUND if the job is expected
2180 to be CPU-bound, or ERL_NIF_DIRTY_JOB_IO_BOUND for jobs that
2181 will be I/O-bound. If dirty scheduler threads are not avail‐
2182 able in the emulator, an attempt to schedule such a job re‐
2183 sults in a notsup exception.
2184 argc and argv:
2186 Can either be the originals passed into the calling NIF, or
2187 can be values created by the calling NIF.
2188 The calling NIF must use the return value of enif_schedule_nif
2190 as its own return value.
2191 Be aware that enif_schedule_nif, as its name implies, only
2193 schedules the NIF for future execution. The calling NIF does not
2194 block waiting for the scheduled NIF to execute and return. This
2195 means that the calling NIF cannot expect to receive the sched‐
2196 uled NIF return value and use it for further operations.
2197 int enif_select(ErlNifEnv* env, ErlNifEvent event, enum ErlNifSelect‐
2199 Flags mode, void* obj, const ErlNifPid* pid, ERL_NIF_TERM ref)
2200 This function can be used to receive asynchronous notifications
2202 when OS-specific event objects become ready for either read or
2203 write operations.
2204 Argument event identifies the event object. On Unix systems, the
2206 functions select/poll are used. The event object must be a
2207 socket, pipe or other file descriptor object that select/poll
2208 can use.
2209 Argument mode describes the type of events to wait for. It can
2211 be ERL_NIF_SELECT_READ, ERL_NIF_SELECT_WRITE or a bitwise OR
2212 combination to wait for both. It can also be ERL_NIF_SELECT_STOP
2213 or ERL_NIF_SELECT_CANCEL which are described further below. When
2214 a read or write event is triggered, a notification message like
2215 this is sent to the process identified by pid:
2216 {select, Obj, Ref, ready_input | ready_output}
2218 ready_input or ready_output indicates if the event object is
2220 ready for reading or writing.
2221 Note:
2223 For complete control over the message format use the newer func‐
2224 tions enif_select_read or enif_select_write introduced in
2225 erts-11.0 (OTP-22.0).
2226 Argument pid may be NULL to indicate the calling process. It
2229 must not be set as undefined.
2230 Argument obj is a resource object obtained from enif_alloc_re‐
2232 source. The purpose of the resource objects is as a container of
2233 the event object to manage its state and lifetime. A handle to
2234 the resource is received in the notification message as Obj.
2235 Argument ref must be either a reference obtained from er‐
2237 lang:make_ref/0 or the atom undefined. It will be passed as Ref
2238 in the notifications. If a selective receive statement is used
2239 to wait for the notification then a reference created just be‐
2240 fore the receive will exploit a runtime optimization that by‐
2241 passes all earlier received messages in the queue.
2242 The notifications are one-shot only. To receive further notifi‐
2244 cations of the same type (read or write), repeated calls to
2245 enif_select must be made after receiving each notification.
2246 ERL_NIF_SELECT_CANCEL can be used to cancel previously selected
2248 events. It must be used in a bitwise OR combination with
2249 ERL_NIF_SELECT_READ and/or ERL_NIF_SELECT_WRITE to indicate
2250 which type of event to cancel. Arguments pid and ref are ignored
2251 when ERL_NIF_SELECT_CANCEL is specified. The return value will
2252 tell if the event was actualy cancelled or if a notification may
2253 already have been sent.
2254 Use ERL_NIF_SELECT_STOP as mode in order to safely close an
2256 event object that has been passed to enif_select. The stop call‐
2257 back of the resource obj will be called when it is safe to close
2258 the event object. This safe way of closing event objects must be
2259 used even if all notifications have been received (or cancelled)
2260 and no further calls to enif_select have been made. ERL_NIF_SE‐
2261 LECT_STOP will first cancel any selected events before it calls
2262 or schedules the stop callback. Arguments pid and ref are ig‐
2263 nored when ERL_NIF_SELECT_STOP is specified.
2264 The first call to enif_select for a specific OS event will es‐
2266 tablish a relation between the event object and the containing
2267 resource. All subsequent calls for an event must pass its con‐
2268 taining resource as argument obj. The relation is dissolved when
2269 enif_select has been called with mode as ERL_NIF_SELECT_STOP and
2270 the corresponding stop callback has returned. A resource can
2271 contain several event objects but one event object can only be
2272 contained within one resource. A resource will not be destructed
2273 until all its contained relations have been dissolved.
2274 Note:
2276 Use enif_monitor_process together with enif_select to detect
2277 failing Erlang processes and prevent them from causing permanent
2278 leakage of resources and their contained OS event objects.
2279 Returns a non-negative value on success where the following bits
2282 can be set:
2283 ERL_NIF_SELECT_STOP_CALLED:
2285 The stop callback was called directly by enif_select.
2286 ERL_NIF_SELECT_STOP_SCHEDULED:
2288 The stop callback was scheduled to run on some other thread
2289 or later by this thread.
2290 ERL_NIF_SELECT_READ_CANCELLED:
2292 A read event was cancelled by ERL_NIF_SELECT_CANCEL or
2293 ERL_NIF_SELECT_STOP and is guaranteed not to generate a
2294 ready_input notification message.
2295 ERL_NIF_SELECT_WRITE_CANCELLED:
2297 A write event was cancelled by ERL_NIF_SELECT_CANCEL or
2298 ERL_NIF_SELECT_STOP and is guaranteed not to generate a
2299 ready_output notification message.
2300 Returns a negative value if the call failed where the following
2302 bits can be set:
2303 ERL_NIF_SELECT_INVALID_EVENT:
2305 Argument event is not a valid OS event object.
2306 ERL_NIF_SELECT_FAILED:
2308 The system call failed to add the event object to the poll
2309 set.
2310 Note:
2312 Use bitwise AND to test for specific bits in the return value.
2313 New significant bits may be added in future releases to give
2314 more detailed information for both failed and successful calls.
2315 Do NOT use equality tests like ==, as that may cause your appli‐
2316 cation to stop working.
2317 Example:
2319 retval = enif_select(env, fd, ERL_NIF_SELECT_STOP, resource, ref);
2321 if (retval < 0) {
2322 /* handle error */
2323 }
2324 /* Success! */
2325 if (retval & ERL_NIF_SELECT_STOP_CALLED) {
2326 /* ... */
2327 }
2328 Note:
2332 The mode flag ERL_NIF_SELECT_CANCEL and the return flags
2333 ERL_NIF_SELECT_READ_CANCELLED and ERL_NIF_SELECT_WRITE_CANCELLED
2334 were introduced in erts-11.0 (OTP-22.0).
2335 int enif_select_read(ErlNifEnv* env, ErlNifEvent event, void* obj,
2338 const ErlNifPid* pid, ERL_NIF_TERM msg, ErlNifEnv* msg_env)
2339 int enif_select_write(ErlNifEnv* env, ErlNifEvent event, void* obj,
2340 const ErlNifPid* pid, ERL_NIF_TERM msg, ErlNifEnv* msg_env)
2341 These are variants of enif_select where you can supply your own
2343 message term msg that will be sent to the process instead of the
2344 predefined tuple {select,_,_,_}.
2345 Argument msg_env must either be NULL or the environment of msg
2347 allocated with enif_alloc_env. If argument msg_env is NULL the
2348 term msg will be copied, otherwise both msg and msg_env will be
2349 invalidated by a successful call to enif_select_read or enif_se‐
2350 lect_write. The environment is then to either be freed with
2351 enif_free_env or cleared for reuse with enif_clear_env. An un‐
2352 successful call will leave msg and msg_env still valid.
2353 Apart from the message format enif_select_read and enif_se‐
2355 lect_write behaves exactly the same as enif_select with argument
2356 mode as either ERL_NIF_SELECT_READ or ERL_NIF_SELECT_WRITE. To
2357 cancel or close events use enif_select.
2358 ErlNifPid *enif_self(ErlNifEnv* caller_env, ErlNifPid* pid)
2360 Initializes the ErlNifPid variable at *pid to represent the
2362 calling process.
2363 Returns pid if successful, or NULL if caller_env is not a
2365 process bound environment.
2366 int enif_send(ErlNifEnv* caller_env,
2368 ErlNifPid* to_pid, ErlNifEnv* msg_env, ERL_NIF_TERM msg)
2369 Sends a message to a process.
2371 caller_env:
2373 The environment of the calling thread (process bound or
2374 callback environment) or NULL if calling from a custom
2375 thread not spawned by ERTS.
2376 *to_pid:
2378 The pid of the receiving process. The pid is to refer to a
2379 process on the local node.
2380 msg_env:
2382 The environment of the message term. Must be a process inde‐
2383 pendent environment allocated with enif_alloc_env or NULL.
2384 msg:
2386 The message term to send.
2387 Returns true if the message is successfully sent. Returns false
2389 if the send operation fails, that is:
2390 * *to_pid does not refer to an alive local process.
2392 * The currently executing process (that is, the sender) is not
2394 alive.
2395 The message environment msg_env with all its terms (including
2397 msg) is invalidated by a successful call to enif_send. The envi‐
2398 ronment is to either be freed with enif_free_env or cleared for
2399 reuse with enif_clear_env. An unsuccessful call will leave msg
2400 and msg_env still valid.
2401 If msg_env is set to NULL, the msg term is copied and the origi‐
2403 nal term and its environment is still valid after the call.
2404 This function is only thread-safe when the emulator with SMP
2406 support is used. It can only be used in a non-SMP emulator from
2407 a NIF-calling thread.
2408 Note:
2410 Passing msg_env as NULL is only supported as from ERTS 8.0 (Er‐
2411 lang/OTP 19).
2412 void enif_set_pid_undefined(ErlNifPid* pid)
2415 Sets an ErlNifPid variable as undefined. See enif_is_pid_unde‐
2417 fined.
2418 unsigned enif_sizeof_resource(void* obj)
2420 Gets the byte size of resource object obj obtained by enif_al‐
2422 loc_resource.
2423 int enif_snprintf(char *str, size_t size, const
2425 char *format, ...)
2426 Similar to snprintf but this format string also accepts "%T",
2428 which formats Erlang terms of type ERL_NIF_TERM.
2429 This function is primarily intended for debugging purpose. It is
2431 not recommended to print very large terms with %T. The function
2432 may change errno, even if successful.
2433 void enif_system_info(ErlNifSysInfo
2435 *sys_info_ptr, size_t size)
2436 Same as driver_system_info.
2438 int enif_term_to_binary(ErlNifEnv *env,
2440 ERL_NIF_TERM term, ErlNifBinary *bin)
2441 Allocates a new binary with enif_alloc_binary and stores the re‐
2443 sult of encoding term according to the Erlang external term for‐
2444 mat.
2445 Returns true on success, or false if the allocation fails.
2447 See also erlang:term_to_binary/1 and enif_binary_to_term.
2449 ErlNifTermType enif_term_type(ErlNifEnv *env, ERL_NIF_TERM term)
2451 Determines the type of the given term. The term must be an ordi‐
2453 nary Erlang term and not one of the special terms returned by
2454 enif_raise_exception, enif_schedule_nif, or similar.
2455 The following types are defined at the moment:
2457 ERL_NIF_TERM_TYPE_ATOM:
2459 ERL_NIF_TERM_TYPE_BITSTRING:
2462 A bitstring or binary
2463 ERL_NIF_TERM_TYPE_FLOAT:
2465 ERL_NIF_TERM_TYPE_FUN:
2468 ERL_NIF_TERM_TYPE_INTEGER:
2471 ERL_NIF_TERM_TYPE_LIST:
2474 A list, empty or not
2475 ERL_NIF_TERM_TYPE_MAP:
2477 ERL_NIF_TERM_TYPE_PID:
2480 ERL_NIF_TERM_TYPE_PORT:
2483 ERL_NIF_TERM_TYPE_REFERENCE:
2486 ERL_NIF_TERM_TYPE_TUPLE:
2489 Note that new types may be added in the future, so the caller
2492 must be prepared to handle unknown types.
2493 int enif_thread_create(char *name,ErlNifTid
2495 *tid,void * (*func)(void *),void *args,ErlNifThreadOpts
2496 *opts)
2497 Same as erl_drv_thread_create.
2499 void enif_thread_exit(void *resp)
2501 Same as erl_drv_thread_exit.
2503 int enif_thread_join(ErlNifTid, void **respp)
2505 Same as erl_drv_thread_join.
2507 char*enif_thread_name(ErlNifTid tid)
2509 Same as erl_drv_thread_name.
2511 ErlNifThreadOpts *enif_thread_opts_create(char *name)
2513 Same as erl_drv_thread_opts_create.
2515 void enif_thread_opts_destroy(ErlNifThreadOpts *opts)
2517 Same as erl_drv_thread_opts_destroy.
2519 ErlNifTid enif_thread_self(void)
2521 Same as erl_drv_thread_self.
2523 int enif_thread_type(void)
2525 Determine the type of currently executing thread. A positive
2527 value indicates a scheduler thread while a negative value or
2528 zero indicates another type of thread. Currently the following
2529 specific types exist (which may be extended in the future):
2530 ERL_NIF_THR_UNDEFINED:
2532 Undefined thread that is not a scheduler thread.
2533 ERL_NIF_THR_NORMAL_SCHEDULER:
2535 A normal scheduler thread.
2536 ERL_NIF_THR_DIRTY_CPU_SCHEDULER:
2538 A dirty CPU scheduler thread.
2539 ERL_NIF_THR_DIRTY_IO_SCHEDULER:
2541 A dirty I/O scheduler thread.
2542 ErlNifTime enif_time_offset(ErlNifTimeUnit time_unit)
2544 Returns the current time offset between Erlang monotonic time
2546 and Erlang system time converted into the time_unit passed as
2547 argument.
2548 time_unit is the time unit of the returned value.
2550 Returns ERL_NIF_TIME_ERROR if called with an invalid time unit
2552 argument or if called from a thread that is not a scheduler
2553 thread.
2554 See also ErlNifTime and ErlNifTimeUnit.
2556 void *enif_tsd_get(ErlNifTSDKey key)
2558 Same as erl_drv_tsd_get.
2560 int enif_tsd_key_create(char *name, ErlNifTSDKey *key)
2562 Same as erl_drv_tsd_key_create.
2564 void enif_tsd_key_destroy(ErlNifTSDKey key)
2566 Same as erl_drv_tsd_key_destroy.
2568 void enif_tsd_set(ErlNifTSDKey key, void *data)
2570 Same as erl_drv_tsd_set.
2572 int enif_vfprintf(FILE *stream, const char *format, va_list ap)
2574 Equivalent to enif_fprintf except that its called with a va_list
2577 instead of a variable number of arguments.
2578 int enif_vsnprintf(char *str, size_t size, const char *format, va_list
2580 ap)
2581 Equivalent to enif_snprintf except that its called with a
2584 va_list instead of a variable number of arguments.
2585 int enif_whereis_pid(ErlNifEnv *caller_env,
2587 ERL_NIF_TERM name, ErlNifPid *pid)
2588 Looks up a process by its registered name.
2590 caller_env:
2592 The environment of the calling thread (process bound or
2593 callback environment) or NULL if calling from a custom
2594 thread not spawned by ERTS.
2595 name:
2597 The name of a registered process, as an atom.
2598 *pid:
2600 The ErlNifPid in which the resolved process id is stored.
2601 On success, sets *pid to the local process registered with name
2603 and returns true. If name is not a registered process, or is not
2604 an atom, false is returned and *pid is unchanged.
2605 Works as erlang:whereis/1, but restricted to processes. See
2607 enif_whereis_port to resolve registered ports.
2608 int enif_whereis_port(ErlNifEnv *caller_env,
2610 ERL_NIF_TERM name, ErlNifPort *port)
2611 Looks up a port by its registered name.
2613 caller_env:
2615 The environment of the calling thread (process bound or
2616 callback environment) or NULL if calling from a custom
2617 thread not spawned by ERTS.
2618 name:
2620 The name of a registered port, as an atom.
2621 *port:
2623 The ErlNifPort in which the resolved port id is stored.
2624 On success, sets *port to the port registered with name and re‐
2626 turns true. If name is not a registered port, or is not an atom,
2627 false is returned and *port is unchanged.
2628 Works as erlang:whereis/1, but restricted to ports. See
2630 enif_whereis_pid to resolve registered processes.
2631
2633 erlang:load_nif/2
2634Ericsson AB erts 11.2.2.2 erl_nif(3)