1erl_driver(3) C Library Functions erl_driver(3)
2
6 erl_driver - API functions for an Erlang driver.
7
9 An Erlang driver is a library containing a set of native driver call‐
10 back functions that the Erlang Virtual Machine calls when certain
11 events occur. There can be multiple instances of a driver, each
12 instance is associated with an Erlang port.
13 Warning:
15 Use this functionality with extreme care.
16 A driver callback is executed as a direct extension of the native code
18 of the VM. Execution is not made in a safe environment. The VM cannot
19 provide the same services as provided when executing Erlang code, such
20 as pre-emptive scheduling or memory protection. If the driver callback
21 function does not behave well, the whole VM will misbehave.
22 * A driver callback that crash will crash the whole VM.
24 * An erroneously implemented driver callback can cause a VM internal
26 state inconsistency, which can cause a crash of the VM, or miscel‐
27 laneous misbehaviors of the VM at any point after the call to the
28 driver callback.
29 * A driver callback doing lengthy work before returning degrades
31 responsiveness of the VM and can cause miscellaneous strange behav‐
32 iors. Such strange behaviors include, but are not limited to,
33 extreme memory usage and bad load balancing between schedulers.
34 Strange behaviors that can occur because of lengthy work can also
35 vary between Erlang/OTP releases.
36 As from ERTS 5.5.3 the driver interface has been extended (see extended
38 marker). The extended interface introduces version management, the pos‐
39 sibility to pass capability flags (see driver_flags) to the runtime
40 system at driver initialization, and some new driver API functions.
41 Note:
43 As from ERTS 5.9 old drivers must be recompiled and use the extended
44 interface. They must also be adjusted to the 64-bit capable driver
45 interface.
46 The driver calls back to the emulator, using the API functions declared
49 in erl_driver.h. They are used for outputting data from the driver,
50 using timers, and so on.
51 Each driver instance is associated with a port. Every port has a port
53 owner process. Communication with the port is normally done through the
54 port owner process. Most of the functions take the port handle as an
55 argument. This identifies the driver instance. Notice that this port
56 handle must be stored by the driver, it is not given when the driver is
57 called from the emulator (see driver_entry).
58 Some of the functions take a parameter of type ErlDrvBinary, a driver
60 binary. It is to be both allocated and freed by the caller. Using a
61 binary directly avoids one extra copying of data.
62 Many of the output functions have a "header buffer", with hbuf and hlen
64 parameters. This buffer is sent as a list before the binary (or list,
65 depending on port mode) that is sent. This is convenient when matching
66 on messages received from the port. (Although in the latest Erlang ver‐
67 sions there is the binary syntax, which enables you to match on the
68 beginning of a binary.)
69 In the runtime system with SMP support, drivers are locked either on
71 driver level or port level (driver instance level). By default driver
72 level locking will be used, that is, only one emulator thread will exe‐
73 cute code in the driver at a time. If port level locking is used, mul‐
74 tiple emulator threads can execute code in the driver at the same time.
75 Only one thread at a time will call driver callbacks corresponding to
76 the same port, though. To enable port level locking, set the
77 ERL_DRV_FLAG_USE_PORT_LOCKING driver flag in the driver_entry used by
78 the driver. When port level locking is used, the driver writer is
79 responsible for synchronizing all accesses to data shared by the ports
80 (driver instances).
81 Most drivers written before the runtime system with SMP support existed
83 can run in the runtime system with SMP support, without being rewrit‐
84 ten, if driver level locking is used.
85 Note:
87 It is assumed that drivers do not access other drivers. If drivers
88 access each other, they must provide their own mechanism for thread-
89 safe synchronization. Such "inter-driver communication" is strongly
90 discouraged.
91 Previously, in the runtime system without SMP support, specific driver
94 callbacks were always called from the same thread. This is not the case
95 in the runtime system with SMP support. Regardless of locking scheme
96 used, calls to driver callbacks can be made from different threads. For
97 example, two consecutive calls to exactly the same callback for exactly
98 the same port can be made from two different threads. This is for most
99 drivers not a problem, but it can be. Drivers that depend on all call‐
100 backs that are called in the same thread, must be rewritten before they
101 are used in the runtime system with SMP support.
102 Note:
104 Regardless of locking scheme used, calls to driver callbacks can be
105 made from different threads.
106 Most functions in this API are not thread-safe, that is, they cannot be
109 called from arbitrary threads. Functions that are not documented as
110 thread-safe can only be called from driver callbacks or function calls
111 descending from a driver callback call. Notice that driver callbacks
112 can be called from different threads. This, however, is not a problem
113 for any function in this API, as the emulator has control over these
114 threads.
115 Warning:
117 Functions not explicitly documented as thread-safe are not thread safe.
118 Also notice that some functions are only thread-safe when used in a
119 runtime system with SMP support.
120 A function not explicitly documented as thread-safe can, at some point
122 in time, have a thread-safe implementation in the runtime system. Such
123 an implementation can however change to a thread unsafe implementation
124 at any time without any notice.
125 Only use functions explicitly documented as thread-safe from arbitrary
127 threads.
128 As mentioned in the warning text at the beginning of this section, it
131 is of vital importance that a driver callback returns relatively fast.
132 It is difficult to give an exact maximum amount of time that a driver
133 callback is allowed to work, but usually a well-behaving driver call‐
134 back is to return within 1 millisecond. This can be achieved using dif‐
135 ferent approaches. If you have full control over the code to execute in
136 the driver callback, the best approach is to divide the work into mul‐
137 tiple chunks of work, and trigger multiple calls to the time-out call‐
138 back using zero time-outs. Function erl_drv_consume_timeslice can be
139 useful to determine when to trigger such time-out callback calls. How‐
140 ever, sometimes it cannot be implemented this way, for example when
141 calling third-party libraries. In this case, you typically want to dis‐
142 patch the work to another thread. Information about thread primitives
143 is provided below.
144
146 All functions that a driver needs to do with Erlang are performed
147 through driver API functions. Functions exist for the following func‐
148 tionality:
149 Timer functions:
151 Control the timer that a driver can use. The timer has the emulator
152 call the timeout entry function after a specified time. Only one
153 timer is available for each driver instance.
154 Queue handling:
156 Every driver instance has an associated queue. This queue is a Sys‐
157 IOVec, which works as a buffer. It is mostly used for the driver to
158 buffer data that is to be written to a device, it is a byte stream.
159 If the port owner process closes the driver, and the queue is not
160 empty, the driver is not closed. This enables the driver to flush
161 its buffers before closing.
162 The queue can be manipulated from any threads if a port data lock
164 is used. For more information, see ErlDrvPDL.
165 Output functions:
167 With these functions, the driver sends data back to the emulator.
168 The data is received as messages by the port owner process, see
169 erlang:open_port/2. The vector function and the function taking a
170 driver binary are faster, as they avoid copying the data buffer.
171 There is also a fast way of sending terms from the driver, without
172 going through the binary term format.
173 Failure:
175 The driver can exit and signal errors up to Erlang. This is only
176 for severe errors, when the driver cannot possibly keep open.
177 Asynchronous calls:
179 Erlang/OTP R7B and later versions have provision for asynchronous
180 function calls, using a thread pool provided by Erlang. There is
181 also a select call, which can be used for asynchronous drivers.
182 Multi-threading:
184 A POSIX thread like API for multi-threading is provided. The Erlang
185 driver thread API only provides a subset of the functionality pro‐
186 vided by the POSIX thread API. The subset provided is more or less
187 the basic functionality needed for multi-threaded programming:
188 * Threads
190 * Mutexes
192 *
194 Condition variables
195 *
197 Read/write locks
198 *
200 Thread-specific data
201 The Erlang driver thread API can be used in conjunction with the
203 POSIX thread API on UN-ices and with the Windows native thread API
204 on Windows. The Erlang driver thread API has the advantage of being
205 portable, but there can exist situations where you want to use
206 functionality from the POSIX thread API or the Windows native
207 thread API.
208 The Erlang driver thread API only returns error codes when it is
210 reasonable to recover from an error condition. If it is not reason‐
211 able to recover from an error condition, the whole runtime system
212 is terminated. For example, if a create mutex operation fails, an
213 error code is returned, but if a lock operation on a mutex fails,
214 the whole runtime system is terminated.
215 Notice that there is no "condition variable wait with time-out" in
217 the Erlang driver thread API. This because of issues with
218 pthread_cond_timedwait. When the system clock suddenly is changed,
219 it is not always guaranteed that you will wake up from the call as
220 expected. An Erlang runtime system must be able to cope with sudden
221 changes of the system clock. Therefore, we have omitted it from the
222 Erlang driver thread API. In the Erlang driver case, time-outs can
223 and are to be handled with the timer functionality of the Erlang
224 driver API.
225 In order for the Erlang driver thread API to function, thread sup‐
227 port must be enabled in the runtime system. An Erlang driver can
228 check if thread support is enabled by use of driver_system_info.
229 Notice that some functions in the Erlang driver API are thread-safe
230 only when the runtime system has SMP support, also this information
231 can be retrieved through driver_system_info. Also notice that many
232 functions in the Erlang driver API are not thread-safe, regardless
233 of whether SMP support is enabled or not. If a function is not doc‐
234 umented as thread-safe, it is not thread-safe.
235 Note:
237 When executing in an emulator thread, it is very important that you
238 unlock all locks you have locked before letting the thread out of
239 your control; otherwise you are very likely to deadlock the whole
240 emulator.
241 If you need to use thread-specific data in an emulator thread, only
243 have the thread-specific data set while the thread is under your con‐
244 trol, and clear the thread-specific data before you let the thread
245 out of your control.
246 In the future, debug functionality will probably be integrated with
249 the Erlang driver thread API. All functions that create entities
250 take a name argument. Currently the name argument is unused, but it
251 will be used when the debug functionality is implemented. If you
252 name all entities created well, the debug functionality will be
253 able to give you better error reports.
254 Adding/removing drivers:
256 A driver can add and later remove drivers.
257 Monitoring processes:
259 A driver can monitor a process that does not own a port.
260 Version management:
262 Version management is enabled for drivers that have set the
263 extended_marker field of their driver_entry to
264 ERL_DRV_EXTENDED_MARKER. erl_driver.h defines:
265 * ERL_DRV_EXTENDED_MARKER
267 * ERL_DRV_EXTENDED_MAJOR_VERSION, which is incremented when driver
269 incompatible changes are made to the Erlang runtime system. Nor‐
270 mally it suffices to recompile drivers when
271 ERL_DRV_EXTENDED_MAJOR_VERSION has changed, but it can, under
272 rare circumstances, mean that drivers must be slightly modified.
273 If so, this will of course be documented.
274 * ERL_DRV_EXTENDED_MINOR_VERSION, which is incremented when new
276 features are added. The runtime system uses the minor version of
277 the driver to determine what features to use.
278 The runtime system normally refuses to load a driver if the major
280 versions differ, or if the major versions are equal and the minor
281 version used by the driver is greater than the one used by the run‐
282 time system. Old drivers with lower major versions are however
283 allowed after a bump of the major version during a transition
284 period of two major releases. Such old drivers can, however, fail
285 if deprecated features are used.
286 The emulator refuses to load a driver that does not use the
288 extended driver interface, to allow for 64-bit capable drivers, as
289 incompatible type changes for the callbacks output, control, and
290 call were introduced in Erlang/OTP R15B. A driver written with the
291 old types would compile with warnings and when called return
292 garbage sizes to the emulator, causing it to read random memory and
293 create huge incorrect result blobs.
294 Therefore it is not enough to only recompile drivers written with
296 version management for pre R15B types; the types must be changed in
297 the driver suggesting other rewrites, especially regarding size
298 variables. Investigate all warnings when recompiling.
299 Also, the API driver functions driver_output* and
301 driver_vec_to_buf, driver_alloc/realloc*, and the driver_* queue
302 functions were changed to have larger length arguments and return
303 values. This is a lesser problem, as code that passes smaller types
304 gets them auto-converted in the calls, and as long as the driver
305 does not handle sizes that overflow an int, all will work as
306 before.
307 Time measurement:
309 Support for time measurement in drivers:
310 * ErlDrvTime
312 * ErlDrvTimeUnit
314 * erl_drv_monotonic_time
316 * erl_drv_time_offset
318 * erl_drv_convert_time_unit
320
322 ERTS 5.9 introduced two new integer types, ErlDrvSizeT and ErlDrvS‐
323 SizeT, which can hold 64-bit sizes if necessary.
324 To not update a driver and only recompile, it probably works when
326 building for a 32-bit machine creating a false sense of security. Hope‐
327 fully that will generate many important warnings. But when recompiling
328 the same driver later on for a 64-bit machine, there will be warnings
329 and almost certainly crashes. So it is a bad idea to postpone updating
330 the driver and not fixing the warnings.
331 When recompiling with gcc, use flag -Wstrict-prototypes to get better
333 warnings. Try to find a similar flag if you use another compiler.
334 The following is a checklist for rewriting a pre ERTS 5.9 driver, most
336 important first:
337 Return types for driver callbacks:
339 Rewrite driver callback control to use return type ErlDrvSSizeT
340 instead of int.
341 Rewrite driver callback call to use return type ErlDrvSSizeT
343 instead of int.
344 Note:
346 These changes are essential not to crash the emulator or worse cause
347 malfunction. Without them a driver can return garbage in the high 32
348 bits to the emulator, causing it to build a huge result from random
349 bytes, either crashing on memory allocation or succeeding with a ran‐
350 dom result from the driver call.
351 Arguments to driver callbacks:
354 Driver callback output now gets ErlDrvSizeT as 3rd argument instead
355 of previously int.
356 Driver callback control now gets ErlDrvSizeT as 4th and 6th argu‐
358 ments instead of previously int.
359 Driver callback call now gets ErlDrvSizeT as 4th and 6th arguments
361 instead of previously int.
362 Sane compiler's calling conventions probably make these changes
364 necessary only for a driver to handle data chunks that require
365 64-bit size fields (mostly larger than 2 GB, as that is what an int
366 of 32 bits can hold). But it is possible to think of non-sane call‐
367 ing conventions that would make the driver callbacks mix up the
368 arguments causing malfunction.
369 Note:
371 The argument type change is from signed to unsigned. This can cause
372 problems for, for example, loop termination conditions or error con‐
373 ditions if you only change the types all over the place.
374 Larger size field in ErlIOVec:
377 The size field in ErlIOVec has been changed to ErlDrvSizeT from
378 int. Check all code that use that field.
379 Automatic type-casting probably makes these changes necessary only
381 for a driver that encounters sizes > 32 bits.
382 Note:
384 The size field changed from signed to unsigned. This can cause prob‐
385 lems for, for example, loop termination conditions or error condi‐
386 tions if you only change the types all over the place.
387 Arguments and return values in the driver API:
390 Many driver API functions have changed argument type and/or return
391 value to ErlDrvSizeT from mostly int. Automatic type-casting proba‐
392 bly makes these changes necessary only for a driver that encounters
393 sizes > 32 bits.
394 driver_output:
396 3rd argument
397 driver_output2:
399 3rd and 5th arguments
400 driver_output_binary:
402 3rd, 5th, and 6th arguments
403 driver_outputv:
405 3rd and 5th arguments
406 driver_vec_to_buf:
408 3rd argument and return value
409 driver_alloc:
411 1st argument
412 driver_realloc:
414 2nd argument
415 driver_alloc_binary:
417 1st argument
418 driver_realloc_binary:
420 2nd argument
421 driver_enq:
423 3rd argument
424 driver_pushq:
426 3rd argument
427 driver_deq:
429 2nd argument and return value
430 driver_sizeq:
432 Return value
433 driver_enq_bin:
435 3rd and 4th arguments
436 driver_pushq_bin:
438 3rd and 4th arguments
439 driver_enqv:
441 3rd argument
442 driver_pushqv:
444 3rd argument
445 driver_peekqv:
447 Return value
448 Note:
450 This is a change from signed to unsigned. This can cause problems
451 for, for example, loop termination conditions and error conditions if
452 you only change the types all over the place.
453
456 ErlDrvSizeT:
457 An unsigned integer type to be used as size_t.
458 ErlDrvSSizeT:
460 A signed integer type, the size of ErlDrvSizeT.
461 ErlDrvSysInfo:
463 typedef struct ErlDrvSysInfo {
466 int driver_major_version;
467 int driver_minor_version;
468 char *erts_version;
469 char *otp_release;
470 int thread_support;
471 int smp_support;
472 int async_threads;
473 int scheduler_threads;
474 int nif_major_version;
475 int nif_minor_version;
476 int dirty_scheduler_support;
477 } ErlDrvSysInfo;
478 The ErlDrvSysInfo structure is used for storage of information
480 about the Erlang runtime system. driver_system_info writes the sys‐
481 tem information when passed a reference to a ErlDrvSysInfo struc‐
482 ture. The fields in the structure are as follows:
483 driver_major_version:
485 The value of ERL_DRV_EXTENDED_MAJOR_VERSION when the runtime sys‐
486 tem was compiled. This value is the same as the value of
487 ERL_DRV_EXTENDED_MAJOR_VERSION used when compiling the driver;
488 otherwise the runtime system would have refused to load the
489 driver.
490 driver_minor_version:
492 The value of ERL_DRV_EXTENDED_MINOR_VERSION when the runtime sys‐
493 tem was compiled. This value can differ from the value of
494 ERL_DRV_EXTENDED_MINOR_VERSION used when compiling the driver.
495 erts_version:
497 A string containing the version number of the runtime system (the
498 same as returned by erlang:system_info(version)).
499 otp_release:
501 A string containing the OTP release number (the same as returned
502 by erlang:system_info(otp_release)).
503 thread_support:
505 A value != 0 if the runtime system has thread support; otherwise
506 0.
507 smp_support:
509 A value != 0 if the runtime system has SMP support; otherwise 0.
510 async_threads:
512 The number of async threads in the async thread pool used by
513 driver_async (the same as returned by erlang:sys‐
514 tem_info(thread_pool_size)).
515 scheduler_threads:
517 The number of scheduler threads used by the runtime system (the
518 same as returned by erlang:system_info(schedulers)).
519 nif_major_version:
521 The value of ERL_NIF_MAJOR_VERSION when the runtime system was
522 compiled.
523 nif_minor_version:
525 The value of ERL_NIF_MINOR_VERSION when the runtime system was
526 compiled.
527 dirty_scheduler_support:
529 A value != 0 if the runtime system has support for dirty sched‐
530 uler threads; otherwise 0.
531 ErlDrvBinary:
533 typedef struct ErlDrvBinary {
536 ErlDrvSint orig_size;
537 char orig_bytes[];
538 } ErlDrvBinary;
539 The ErlDrvBinary structure is a binary, as sent between the emula‐
541 tor and the driver. All binaries are reference counted; when
542 driver_binary_free is called, the reference count is decremented,
543 when it reaches zero, the binary is deallocated. orig_size is the
544 binary size and orig_bytes is the buffer. ErlDrvBinary has not a
545 fixed size, its size is orig_size + 2 * sizeof(int).
546 Note:
548 The refc field has been removed. The reference count of an ErlDrvBi‐
549 nary is now stored elsewhere. The reference count of an ErlDrvBinary
550 can be accessed through driver_binary_get_refc,
551 driver_binary_inc_refc, and driver_binary_dec_refc.
552 Some driver calls, such as driver_enq_binary, increment the driver
555 reference count, and others, such as driver_deq decrement it.
556 Using a driver binary instead of a normal buffer is often faster,
558 as the emulator needs not to copy the data, only the pointer is
559 used.
560 A driver binary allocated in the driver, with driver_alloc_binary,
562 is to be freed in the driver (unless otherwise stated) with
563 driver_free_binary. (Notice that this does not necessarily deallo‐
564 cate it, if the driver is still referred in the emulator, the ref-
565 count will not go to zero.)
566 Driver binaries are used in the driver_output2 and driver_outputv
568 calls, and in the queue. Also the driver callback outputv uses
569 driver binaries.
570 If the driver for some reason wants to keep a driver binary around,
572 for example in a static variable, the reference count is to be
573 incremented, and the binary can later be freed in the stop call‐
574 back, with driver_free_binary.
575 Notice that as a driver binary is shared by the driver and the emu‐
577 lator. A binary received from the emulator or sent to the emulator
578 must not be changed by the driver.
579 Since ERTS 5.5 (Erlang/OTP R11B), orig_bytes is guaranteed to be
581 properly aligned for storage of an array of doubles (usually 8-byte
582 aligned).
583 ErlDrvData:
585 A handle to driver-specific data, passed to the driver callbacks.
586 It is a pointer, and is most often type cast to a specific pointer
587 in the driver.
588 SysIOVec:
590 A system I/O vector, as used by writev on Unix and WSASend on
591 Win32. It is used in ErlIOVec.
592 ErlIOVec:
594 typedef struct ErlIOVec {
597 int vsize;
598 ErlDrvSizeT size;
599 SysIOVec* iov;
600 ErlDrvBinary** binv;
601 } ErlIOVec;
602 The I/O vector used by the emulator and drivers is a list of bina‐
604 ries, with a SysIOVec pointing to the buffers of the binaries. It
605 is used in driver_outputv and the outputv driver callback. Also,
606 the driver queue is an ErlIOVec.
607 ErlDrvMonitor:
609 When a driver creates a monitor for a process, a ErlDrvMonitor is
610 filled in. This is an opaque data type that can be assigned to, but
611 not compared without using the supplied compare function (that is,
612 it behaves like a struct).
613 The driver writer is to provide the memory for storing the monitor
615 when calling driver_monitor_process. The address of the data is not
616 stored outside of the driver, so ErlDrvMonitor can be used as any
617 other data, it can be copied, moved in memory, forgotten, and so
618 on.
619 ErlDrvNowData:
621 The ErlDrvNowData structure holds a time stamp consisting of three
622 values measured from some arbitrary point in the past. The three
623 structure members are:
624 megasecs:
626 The number of whole megaseconds elapsed since the arbitrary point
627 in time
628 secs:
630 The number of whole seconds elapsed since the arbitrary point in
631 time
632 microsecs:
634 The number of whole microseconds elapsed since the arbitrary
635 point in time
636 ErlDrvPDL:
638 If certain port-specific data must be accessed from other threads
639 than those calling the driver callbacks, a port data lock can be
640 used to synchronize the operations on the data. Currently, the only
641 port-specific data that the emulator associates with the port data
642 lock is the driver queue.
643 Normally a driver instance has no port data lock. If the driver
645 instance wants to use a port data lock, it must create the port
646 data lock by calling driver_pdl_create.
647 Note:
649 Once the port data lock has been created, every access to data asso‐
650 ciated with the port data lock must be done while the port data lock
651 is locked. The port data lock is locked and unlocked by
652 driver_pdl_lock, and driver_pdl_unlock, respectively.
653 A port data lock is reference counted, and when the reference count
656 reaches zero, it is destroyed. The emulator at least increments the
657 reference count once when the lock is created and decrements it
658 once the port associated with the lock terminates. The emulator
659 also increments the reference count when an async job is enqueued
660 and decrements it when an async job has been invoked. Also, the
661 driver is responsible for ensuring that the reference count does
662 not reach zero before the last use of the lock by the driver has
663 been made. The reference count can be read, incremented, and decre‐
664 mented by driver_pdl_get_refc, driver_pdl_inc_refc, and
665 driver_pdl_dec_refc, respectively.
666 ErlDrvTid:
668 Thread identifier.
669 See also erl_drv_thread_create, erl_drv_thread_exit,
671 erl_drv_thread_join, erl_drv_thread_self, and erl_drv_equal_tids.
672 ErlDrvThreadOpts:
674 int suggested_stack_size;
677 Thread options structure passed to erl_drv_thread_create. The fol‐
679 lowing field exists:
680 suggested_stack_size:
682 A suggestion, in kilowords, on how large a stack to use. A value
683 < 0 means default size.
684 See also erl_drv_thread_opts_create, erl_drv_thread_opts_destroy,
686 and erl_drv_thread_create.
687 ErlDrvMutex:
689 Mutual exclusion lock. Used for synchronizing access to shared
690 data. Only one thread at a time can lock a mutex.
691 See also erl_drv_mutex_create, erl_drv_mutex_destroy,
693 erl_drv_mutex_lock, erl_drv_mutex_trylock, and
694 erl_drv_mutex_unlock.
695 ErlDrvCond:
697 Condition variable. Used when threads must wait for a specific con‐
698 dition to appear before continuing execution. Condition variables
699 must be used with associated mutexes.
700 See also erl_drv_cond_create, erl_drv_cond_destroy,
702 erl_drv_cond_signal, erl_drv_cond_broadcast, and erl_drv_cond_wait.
703 ErlDrvRWLock:
705 Read/write lock. Used to allow multiple threads to read shared data
706 while only allowing one thread to write the same data. Multiple
707 threads can read lock an rwlock at the same time, while only one
708 thread can read/write lock an rwlock at a time.
709 See also erl_drv_rwlock_create, erl_drv_rwlock_destroy,
711 erl_drv_rwlock_rlock, erl_drv_rwlock_tryrlock, erl_drv_rwlock_run‐
712 lock, erl_drv_rwlock_rwlock, erl_drv_rwlock_tryrwlock, and
713 erl_drv_rwlock_rwunlock.
714 ErlDrvTSDKey:
716 Key that thread-specific data can be associated with.
717 See also erl_drv_tsd_key_create, erl_drv_tsd_key_destroy,
719 erl_drv_tsd_set, and erl_drv_tsd_get.
720 ErlDrvTime:
722 A signed 64-bit integer type for time representation.
723 ErlDrvTimeUnit:
725 An enumeration of time units supported by the driver API:
726 ERL_DRV_SEC:
728 Seconds
729 ERL_DRV_MSEC:
731 Milliseconds
732 ERL_DRV_USEC:
734 Microseconds
735 ERL_DRV_NSEC:
737 Nanoseconds
738
740 void add_driver_entry(ErlDrvEntry
741 *de)
742 Adds a driver entry to the list of drivers known by Erlang. The
744 init function of parameter de is called.
745 Note:
747 To use this function for adding drivers residing in dynamically
748 loaded code is dangerous. If the driver code for the added
749 driver resides in the same dynamically loaded module (that is,
750 .so file) as a normal dynamically loaded driver (loaded with the
751 erl_ddll interface), the caller is to call driver_lock_driver
752 before adding driver entries.
753 Use of this function is generally deprecated.
755 void *driver_alloc(ErlDrvSizeT size)
758 Allocates a memory block of the size specified in size, and
760 returns it. This fails only on out of memory, in which case NULL
761 is returned. (This is most often a wrapper for malloc).
762 Memory allocated must be explicitly freed with a corresponding
764 call to driver_free (unless otherwise stated).
765 This function is thread-safe.
767 ErlDrvBinary *driver_alloc_binary(ErlDrvSizeT size)
769 Allocates a driver binary with a memory block of at least size
771 bytes, and returns a pointer to it, or NULL on failure (out of
772 memory). When a driver binary has been sent to the emulator, it
773 must not be changed. Every allocated binary is to be freed by a
774 corresponding call to driver_free_binary (unless otherwise
775 stated).
776 Notice that a driver binary has an internal reference counter.
778 This means that calling driver_free_binary, it may not actually
779 dispose of it. If it is sent to the emulator, it can be refer‐
780 enced there.
781 The driver binary has a field, orig_bytes, which marks the start
783 of the data in the binary.
784 This function is thread-safe.
786 long driver_async(ErlDrvPort port, unsigned
788 int* key, void (*async_invoke)(void*), void* async_data, void
789 (*async_free)(void*))
790 Performs an asynchronous call. The function async_invoke is
792 invoked in a thread separate from the emulator thread. This
793 enables the driver to perform time-consuming, blocking opera‐
794 tions without blocking the emulator.
795 The async thread pool size can be set with command-line argument
797 +A in erl(1). If an async thread pool is unavailable, the call
798 is made synchronously in the thread calling driver_async. The
799 current number of async threads in the async thread pool can be
800 retrieved through driver_system_info.
801 If a thread pool is available, a thread is used. If argument key
803 is NULL, the threads from the pool are used in a round-robin
804 way, each call to driver_async uses the next thread in the pool.
805 With argument key set, this behavior is changed. The two same
806 values of *key always get the same thread.
807 To ensure that a driver instance always uses the same thread,
809 the following call can be used:
810 unsigned int myKey = driver_async_port_key(myPort);
812 r = driver_async(myPort, &myKey, myData, myFunc);
814 It is enough to initialize myKey once for each driver instance.
816 If a thread is already working, the calls are queued up and exe‐
818 cuted in order. Using the same thread for each driver instance
819 ensures that the calls are made in sequence.
820 The async_data is the argument to the functions async_invoke and
822 async_free. It is typically a pointer to a structure containing
823 a pipe or event that can be used to signal that the async opera‐
824 tion completed. The data is to be freed in async_free.
825 When the async operation is done, ready_async driver entry func‐
827 tion is called. If ready_async is NULL in the driver entry, the
828 async_free function is called instead.
829 The return value is -1 if the driver_async call fails.
831 Note:
833 As from ERTS 5.5.4.3 the default stack size for threads in the
834 async-thread pool is 16 kilowords, that is, 64 kilobyte on
835 32-bit architectures. This small default size has been chosen
836 because the amount of async-threads can be quite large. The
837 default stack size is enough for drivers delivered with
838 Erlang/OTP, but is possibly not sufficiently large for other
839 dynamically linked-in drivers that use the driver_async func‐
840 tionality. A suggested stack size for threads in the async-
841 thread pool can be configured through command-line argument +a
842 in erl(1).
843 unsigned int driver_async_port_key(ErlDrvPort
846 port)
847 Calculates a key for later use in driver_async. The keys are
849 evenly distributed so that a fair mapping between port IDs and
850 async thread IDs is achieved.
851 Note:
853 Before Erlang/OTP R16, the port ID could be used as a key with
854 proper casting, but after the rewrite of the port subsystem,
855 this is no longer the case. With this function, you can achieve
856 the same distribution based on port IDs as before Erlang/OTP
857 R16.
858 long driver_binary_dec_refc(ErlDrvBinary *bin)
861 Decrements the reference count on bin and returns the reference
863 count reached after the decrement.
864 This function is thread-safe.
866 Note:
868 The reference count of driver binary is normally to be decre‐
869 mented by calling driver_free_binary.
870 driver_binary_dec_refc does not free the binary if the reference
872 count reaches zero. Only use driver_binary_dec_refc when you are
873 sure not to reach a reference count of zero.
874 long driver_binary_get_refc(ErlDrvBinary *bin)
877 Returns the current reference count on bin.
879 This function is thread-safe.
881 long driver_binary_inc_refc(ErlDrvBinary *bin)
883 Increments the reference count on bin and returns the reference
885 count reached after the increment.
886 This function is thread-safe.
888 ErlDrvTermData driver_caller(ErlDrvPort
890 port)
891 Returns the process ID of the process that made the current call
893 to the driver. The process ID can be used with driver_send_term
894 to send back data to the caller. driver_caller only returns
895 valid data when currently executing in one of the following
896 driver callbacks:
897 start:
899 Called from erlang:open_port/2.
900 output:
902 Called from erlang:send/2 and erlang:port_command/2.
903 outputv:
905 Called from erlang:send/2 and erlang:port_command/2.
906 control:
908 Called from erlang:port_control/3.
909 call:
911 Called from erlang:port_call/3.
912 Notice that this function is not thread-safe, not even when the
914 emulator with SMP support is used.
915 int driver_cancel_timer(ErlDrvPort port)
917 Cancels a timer set with driver_set_timer.
919 The return value is 0.
921 int driver_compare_monitors(const ErlDrvMonitor
923 *monitor1, const ErlDrvMonitor *monitor2)
924 Compares two ErlDrvMonitors. Can also be used to imply some
926 artificial order on monitors, for whatever reason.
927 Returns 0 if monitor1 and monitor2 are equal, < 0 if monitor1 <
929 monitor2, and > 0 if monitor1 > monitor2.
930 ErlDrvTermData driver_connected(ErlDrvPort
932 port)
933 Returns the port owner process.
935 Notice that this function is not thread-safe, not even when the
937 emulator with SMP support is used.
938 ErlDrvPort driver_create_port(ErlDrvPort port,
940 ErlDrvTermData owner_pid, char* name,
941 ErlDrvData drv_data)
942 Creates a new port executing the same driver code as the port
944 creating the new port.
945 port:
947 The port handle of the port (driver instance) creating the
948 new port.
949 owner_pid:
951 The process ID of the Erlang process to become owner of the
952 new port. This process will be linked to the new port. You
953 usually want to use driver_caller(port) as owner_pid.
954 name:
956 The port name of the new port. You usually want to use the
957 same port name as the driver name (driver_name field of the
958 driver_entry).
959 drv_data:
961 The driver-defined handle that is passed in later calls to
962 driver callbacks. Notice that the driver start callback is
963 not called for this new driver instance. The driver-defined
964 handle is normally created in the driver start callback when
965 a port is created through erlang:open_port/2.
966 The caller of driver_create_port is allowed to manipulate the
968 newly created port when driver_create_port has returned. When
969 port level locking is used, the creating port is only allowed to
970 manipulate the newly created port until the current driver call‐
971 back, which was called by the emulator, returns.
972 int driver_demonitor_process(ErlDrvPort port,
974 const ErlDrvMonitor *monitor)
975 Cancels a monitor created earlier.
977 Returns 0 if a monitor was removed and > 0 if the monitor no
979 longer exists.
980 ErlDrvSizeT driver_deq(ErlDrvPort port,
982 ErlDrvSizeT size)
983 Dequeues data by moving the head pointer forward in the driver
985 queue by size bytes. The data in the queue is deallocated.
986 Returns the number of bytes remaining in the queue on success,
988 otherwise -1.
989 This function can be called from any thread if a port data lock
991 associated with the port is locked by the calling thread during
992 the call.
993 int driver_enq(ErlDrvPort port, char* buf,
995 ErlDrvSizeT len)
996 Enqueues data in the driver queue. The data in buf is copied
998 (len bytes) and placed at the end of the driver queue. The
999 driver queue is normally used in a FIFO way.
1000 The driver queue is available to queue output from the emulator
1002 to the driver (data from the driver to the emulator is queued by
1003 the emulator in normal Erlang message queues). This can be use‐
1004 ful if the driver must wait for slow devices, and so on, and
1005 wants to yield back to the emulator. The driver queue is imple‐
1006 mented as an ErlIOVec.
1007 When the queue contains data, the driver does not close until
1009 the queue is empty.
1010 The return value is 0.
1012 This function can be called from any thread if a port data lock
1014 associated with the port is locked by the calling thread during
1015 the call.
1016 int driver_enq_bin(ErlDrvPort port,
1018 ErlDrvBinary *bin, ErlDrvSizeT offset, ErlDrvSizeT len)
1019 Enqueues a driver binary in the driver queue. The data in bin at
1021 offset with length len is placed at the end of the queue. This
1022 function is most often faster than driver_enq, because no data
1023 must be copied.
1024 This function can be called from any thread if a port data lock
1026 associated with the port is locked by the calling thread during
1027 the call.
1028 The return value is 0.
1030 int driver_enqv(ErlDrvPort port, ErlIOVec *ev,
1032 ErlDrvSizeT skip)
1033 Enqueues the data in ev, skipping the first skip bytes of it, at
1035 the end of the driver queue. It is faster than driver_enq,
1036 because no data must be copied.
1037 The return value is 0.
1039 This function can be called from any thread if a port data lock
1041 associated with the port is locked by the calling thread during
1042 the call.
1043 int driver_failure(ErlDrvPort port, int
1045 error)
1046 int driver_failure_atom(ErlDrvPort port, char
1047 *string)
1048 int driver_failure_posix(ErlDrvPort port, int
1049 error)
1050 Signals to Erlang that the driver has encountered an error and
1052 is to be closed. The port is closed and the tuple {'EXIT',
1053 error, Err} is sent to the port owner process, where error is an
1054 error atom (driver_failure_atom and driver_failure_posix) or an
1055 integer (driver_failure).
1056 The driver is to fail only when in severe error situations, when
1058 the driver cannot possibly keep open, for example, buffer allo‐
1059 cation gets out of memory. For normal errors it is more appro‐
1060 priate to send error codes with driver_output.
1061 The return value is 0.
1063 int driver_failure_eof(ErlDrvPort
1065 port)
1066 Signals to Erlang that the driver has encountered an EOF and is
1068 to be closed, unless the port was opened with option eof, in
1069 which case eof is sent to the port. Otherwise the port is closed
1070 and an 'EXIT' message is sent to the port owner process.
1071 The return value is 0.
1073 void driver_free(void *ptr)
1075 Frees the memory pointed to by ptr. The memory is to have been
1077 allocated with driver_alloc. All allocated memory is to be deal‐
1078 located, only once. There is no garbage collection in drivers.
1079 This function is thread-safe.
1081 void driver_free_binary(ErlDrvBinary *bin)
1083 Frees a driver binary bin, allocated previously with
1085 driver_alloc_binary. As binaries in Erlang are reference
1086 counted, the binary can still be around.
1087 This function is thread-safe.
1089 ErlDrvTermData driver_get_monitored_process(ErlDrvPort port, const
1091 ErlDrvMonitor *monitor)
1092 Returns the process ID associated with a living monitor. It can
1094 be used in the process_exit callback to get the process identi‐
1095 fication for the exiting process.
1096 Returns driver_term_nil if the monitor no longer exists.
1098 int driver_get_now(ErlDrvNowData *now)
1100 Warning:
1102 This function is deprecated. Do not use it. Use erl_drv_mono‐
1103 tonic_time (perhaps in combination with erl_drv_time_offset)
1104 instead.
1105 Reads a time stamp into the memory pointed to by parameter now.
1108 For information about specific fields, see ErlDrvNowData.
1109 The return value is 0, unless the now pointer is invalid, in
1111 which case it is < 0.
1112 int driver_lock_driver(ErlDrvPort
1114 port)
1115 Locks the driver used by the port port in memory for the rest of
1117 the emulator process' lifetime. After this call, the driver
1118 behaves as one of Erlang's statically linked-in drivers.
1119 ErlDrvTermData driver_mk_atom(char*
1121 string)
1122 Returns an atom given a name string. The atom is created and
1124 does not change, so the return value can be saved and reused,
1125 which is faster than looking up the atom several times.
1126 Notice that this function is not thread-safe, not even when the
1128 emulator with SMP support is used.
1129 ErlDrvTermData driver_mk_port(ErlDrvPort
1131 port)
1132 Converts a port handle to the Erlang term format, usable in
1134 erl_drv_output_term and erl_drv_send_term.
1135 Notice that this function is not thread-safe, not even when the
1137 emulator with SMP support is used.
1138 int driver_monitor_process(ErlDrvPort port,
1140 ErlDrvTermData process, ErlDrvMonitor *monitor)
1141 Starts monitoring a process from a driver. When a process is
1143 monitored, a process exit results in a call to the provided
1144 process_exit callback in the ErlDrvEntry structure. The ErlDrv‐
1145 Monitor structure is filled in, for later removal or compare.
1146 Parameter process is to be the return value of an earlier call
1148 to driver_caller or driver_connected call.
1149 Returns 0 on success, < 0 if no callback is provided, and > 0 if
1151 the process is no longer alive.
1152 int driver_output(ErlDrvPort port, char *buf,
1154 ErlDrvSizeT len)
1155 Sends data from the driver up to the emulator. The data is
1157 received as terms or binary data, depending on how the driver
1158 port was opened.
1159 The data is queued in the port owner process' message queue.
1161 Notice that this does not yield to the emulator (as the driver
1162 and the emulator run in the same thread).
1163 Parameter buf points to the data to send, and len is the number
1165 of bytes.
1166 The return value for all output functions is 0 for normal use.
1168 If the driver is used for distribution, it can fail and return
1169 -1.
1170 int driver_output_binary(ErlDrvPort port, char
1172 *hbuf, ErlDrvSizeT hlen, ErlDrvBinary* bin, ErlDrvSizeT offset,
1173 ErlDrvSizeT len)
1174 Sends data to a port owner process from a driver binary. It has
1176 a header buffer (hbuf and hlen) just like driver_output2. Param‐
1177 eter hbuf can be NULL.
1178 Parameter offset is an offset into the binary and len is the
1180 number of bytes to send.
1181 Driver binaries are created with driver_alloc_binary.
1183 The data in the header is sent as a list and the binary as an
1185 Erlang binary in the tail of the list.
1186 For example, if hlen is 2, the port owner process receives [H1,
1188 H2 | <<T>>].
1189 The return value is 0 for normal use.
1191 Notice that, using the binary syntax in Erlang, the driver
1193 application can match the header directly from the binary, so
1194 the header can be put in the binary, and hlen can be set to 0.
1195 int driver_output_term(ErlDrvPort port,
1197 ErlDrvTermData* term, int n)
1198 Warning:
1200 This function is deprecated. Use erl_drv_output_terminstead.
1201 Parameters term and n work as in erl_drv_output_term.
1204 Notice that this function is not thread-safe, not even when the
1206 emulator with SMP support is used.
1207 int driver_output2(ErlDrvPort port, char *hbuf,
1209 ErlDrvSizeT hlen, char *buf, ErlDrvSizeT len)
1210 First sends hbuf (length in hlen) data as a list, regardless of
1212 port settings. Then sends buf as a binary or list. For example,
1213 if hlen is 3, the port owner process receives [H1, H2, H3 | T].
1214 The point of sending data as a list header, is to facilitate
1216 matching on the data received.
1217 The return value is 0 for normal use.
1219 int driver_outputv(ErlDrvPort port, char* hbuf,
1221 ErlDrvSizeT hlen, ErlIOVec *ev, ErlDrvSizeT skip)
1222 Sends data from an I/O vector, ev, to the port owner process. It
1224 has a header buffer (hbuf and hlen), just like driver_output2.
1225 Parameter skip is a number of bytes to skip of the ev vector
1227 from the head.
1228 You get vectors of ErlIOVec type from the driver queue (see
1230 below), and the outputv driver entry function. You can also make
1231 them yourself, if you want to send several ErlDrvBinary buffers
1232 at once. Often it is faster to use driver_output or .
1233 For example, if hlen is 2 and ev points to an array of three
1235 binaries, the port owner process receives [H1, H2, <<B1>>,
1236 <<B2>> | <<B3>>].
1237 The return value is 0 for normal use.
1239 The comment for driver_output_binary also applies for
1241 driver_outputv.
1242 ErlDrvPDL driver_pdl_create(ErlDrvPort port)
1244 Creates a port data lock associated with the port.
1246 Note:
1248 Once a port data lock has been created, it must be locked during
1249 all operations on the driver queue of the port.
1250 Returns a newly created port data lock on success, otherwise
1253 NULL. The function fails if port is invalid or if a port data
1254 lock already has been associated with the port.
1255 long driver_pdl_dec_refc(ErlDrvPDL
1257 pdl)
1258 Decrements the reference count of the port data lock passed as
1260 argument (pdl).
1261 The current reference count after the decrement has been per‐
1263 formed is returned.
1264 This function is thread-safe.
1266 long driver_pdl_get_refc(ErlDrvPDL pdl)
1268 Returns the current reference count of the port data lock passed
1270 as argument (pdl).
1271 This function is thread-safe.
1273 long driver_pdl_inc_refc(ErlDrvPDL pdl)
1275 Increments the reference count of the port data lock passed as
1277 argument (pdl).
1278 The current reference count after the increment has been per‐
1280 formed is returned.
1281 This function is thread-safe.
1283 void driver_pdl_lock(ErlDrvPDL pdl)
1285 Locks the port data lock passed as argument (pdl).
1287 This function is thread-safe.
1289 void driver_pdl_unlock(ErlDrvPDL pdl)
1291 Unlocks the port data lock passed as argument (pdl).
1293 This function is thread-safe.
1295 SysIOVec *driver_peekq(ErlDrvPort port, int
1297 *vlen)
1298 Retrieves the driver queue as a pointer to an array of Sys‐
1300 IOVecs. It also returns the number of elements in vlen. This is
1301 one of two ways to get data out of the queue.
1302 Nothing is removed from the queue by this function, that must be
1304 done with driver_deq.
1305 The returned array is suitable to use with the Unix system call
1307 writev.
1308 This function can be called from any thread if a port data lock
1310 associated with the port is locked by the calling thread during
1311 the call.
1312 ErlDrvSizeT driver_peekqv(ErlDrvPort port,
1314 ErlIOVec *ev)
1315 Retrieves the driver queue into a supplied ErlIOVec ev. It also
1317 returns the queue size. This is one of two ways to get data out
1318 of the queue.
1319 If ev is NULL, all ones that is -1 type cast to ErlDrvSizeT are
1321 returned.
1322 Nothing is removed from the queue by this function, that must be
1324 done with driver_deq.
1325 This function can be called from any thread if a port data lock
1327 associated with the port is locked by the calling thread during
1328 the call.
1329 int driver_pushq(ErlDrvPort port, char* buf,
1331 ErlDrvSizeT len)
1332 Puts data at the head of the driver queue. The data in buf is
1334 copied (len bytes) and placed at the beginning of the queue.
1335 The return value is 0.
1337 This function can be called from any thread if a port data lock
1339 associated with the port is locked by the calling thread during
1340 the call.
1341 int driver_pushq_bin(ErlDrvPort port,
1343 ErlDrvBinary *bin, ErlDrvSizeT offset, ErlDrvSizeT len)
1344 Puts data in the binary bin, at offset with length len at the
1346 head of the driver queue. It is most often faster than
1347 driver_pushq, because no data must be copied.
1348 This function can be called from any thread if a port data lock
1350 associated with the port is locked by the calling thread during
1351 the call.
1352 The return value is 0.
1354 int driver_pushqv(ErlDrvPort port, ErlIOVec
1356 *ev, ErlDrvSizeT skip)
1357 Puts the data in ev, skipping the first skip bytes of it, at the
1359 head of the driver queue. It is faster than driver_pushq,
1360 because no data must be copied.
1361 The return value is 0.
1363 This function can be called from any thread if a port data lock
1365 associated with the port is locked by the calling thread during
1366 the call.
1367 int driver_read_timer(ErlDrvPort port, unsigned
1369 long *time_left)
1370 Reads the current time of a timer, and places the result in
1372 time_left. This is the time in milliseconds, before the time-out
1373 occurs.
1374 The return value is 0.
1376 void *driver_realloc(void *ptr, ErlDrvSizeT size)
1378 Resizes a memory block, either in place, or by allocating a new
1380 block, copying the data, and freeing the old block. A pointer is
1381 returned to the reallocated memory. On failure (out of memory),
1382 NULL is returned. (This is most often a wrapper for realloc.)
1383 This function is thread-safe.
1385 ErlDrvBinary *driver_realloc_binary(ErlDrvBinary *bin, ErlDrvSizeT
1387 size)
1388 Resizes a driver binary, while keeping the data.
1391 Returns the resized driver binary on success. Returns NULL on
1393 failure (out of memory).
1394 This function is thread-safe.
1396 int driver_select(ErlDrvPort port, ErlDrvEvent
1398 event, int mode, int on)
1399 This function is used by drivers to provide the emulator with
1401 events to check for. This enables the emulator to call the
1402 driver when something has occurred asynchronously.
1403 Parameter event identifies an OS-specific event object. On Unix
1405 systems, the functions select/poll are used. The event object
1406 must be a socket or pipe (or other object that select/poll can
1407 use). On Windows, the Win32 API function WaitForMultipleObjects
1408 is used. This places other restrictions on the event object; see
1409 the Win32 SDK documentation.
1410 Parameter on is to be 1 for setting events and 0 for clearing
1412 them.
1413 Parameter mode is a bitwise OR combination of ERL_DRV_READ,
1415 ERL_DRV_WRITE, and ERL_DRV_USE. The first two specify whether to
1416 wait for read events and/or write events. A fired read event
1417 calls ready_input and a fired write event calls ready_output.
1418 Note:
1420 Some OS (Windows) do not differentiate between read and write
1421 events. The callback for a fired event then only depends on the
1422 value of mode.
1423 ERL_DRV_USE specifies if we are using the event object or if we
1426 want to close it. On an emulator with SMP support, it is not
1427 safe to clear all events and then close the event object after
1428 driver_select has returned. Another thread can still be using
1429 the event object internally. To safely close an event object,
1430 call driver_select with ERL_DRV_USE and on==0, which clears all
1431 events and then either calls stop_select or schedules it to be
1432 called when it is safe to close the event object. ERL_DRV_USE is
1433 to be set together with the first event for an event object. It
1434 is harmless to set ERL_DRV_USE even if it already has been done.
1435 Clearing all events but keeping ERL_DRV_USE set indicates that
1436 we are using the event object and probably will set events for
1437 it again.
1438 Note:
1440 ERL_DRV_USE was added in Erlang/OTP R13. Old drivers still work
1441 as before, but it is recommended to update them to use
1442 ERL_DRV_USE and stop_select to ensure that event objects are
1443 closed in a safe way.
1444 The return value is 0, unless ready_input/ready_output is NULL,
1447 in which case it is -1.
1448 int driver_send_term(ErlDrvPort port,
1450 ErlDrvTermData receiver, ErlDrvTermData* term, int n)
1451 Warning:
1453 This function is deprecated. Use erl_drv_send_term instead.
1454 Note:
1457 The parameters of this function cannot be properly checked by
1458 the runtime system when executed by arbitrary threads. This can
1459 cause the function not to fail when it should.
1460 Parameters term and n work as in erl_drv_output_term.
1463 This function is only thread-safe when the emulator with SMP
1465 support is used.
1466 int driver_set_timer(ErlDrvPort port, unsigned
1468 long time)
1469 Sets a timer on the driver, which will count down and call the
1471 driver when it is timed out. Parameter time is the time in mil‐
1472 liseconds before the timer expires.
1473 When the timer reaches 0 and expires, the driver entry function
1475 timeout is called.
1476 Notice that only one timer exists on each driver instance; set‐
1478 ting a new timer replaces an older one.
1479 Return value is 0, unless the timeout driver function is NULL,
1481 in which case it is -1.
1482 ErlDrvSizeT driver_sizeq(ErlDrvPort port)
1484 Returns the number of bytes currently in the driver queue.
1486 This function can be called from any thread if a port data lock
1488 associated with the port is locked by the calling thread during
1489 the call.
1490 void driver_system_info(ErlDrvSysInfo
1492 *sys_info_ptr, size_t size)
1493 Writes information about the Erlang runtime system into the Erl‐
1495 DrvSysInfo structure referred to by the first argument. The sec‐
1496 ond argument is to be the size of the ErlDrvSysInfo structure,
1497 that is, sizeof(ErlDrvSysInfo).
1498 For information about specific fields, see ErlDrvSysInfo.
1500 ErlDrvSizeT driver_vec_to_buf(ErlIOVec *ev,
1502 char *buf, ErlDrvSizeT len)
1503 Collects several segments of data, referenced by ev, by copying
1505 them in order to the buffer buf, of the size len.
1506 If the data is to be sent from the driver to the port owner
1508 process, it is faster to use driver_outputv.
1509 The return value is the space left in the buffer, that is, if ev
1511 contains less than len bytes it is the difference, and if ev
1512 contains len bytes or more, it is 0. This is faster if there is
1513 more than one header byte, as the binary syntax can construct
1514 integers directly from the binary.
1515 void erl_drv_busy_msgq_limits(ErlDrvPort port,
1517 ErlDrvSizeT *low, ErlDrvSizeT *high)
1518 Sets and gets limits that will be used for controlling the busy
1520 state of the port message queue.
1521 The port message queue is set into a busy state when the amount
1523 of command data queued on the message queue reaches the high
1524 limit. The port message queue is set into a not busy state when
1525 the amount of command data queued on the message queue falls
1526 below the low limit. Command data is in this context data passed
1527 to the port using either Port ! {Owner, {command, Data}} or
1528 port_command/[2,3]. Notice that these limits only concerns com‐
1529 mand data that have not yet reached the port. The busy port fea‐
1530 ture can be used for data that has reached the port.
1531 Valid limits are values in the range [ERL_DRV_BUSY_MSGQ_LIM_MIN,
1533 ERL_DRV_BUSY_MSGQ_LIM_MAX]. Limits are automatically adjusted to
1534 be sane. That is, the system adjusts values so that the low
1535 limit used is lower than or equal to the high limit used. By
1536 default the high limit is 8 kB and the low limit is 4 kB.
1537 By passing a pointer to an integer variable containing the value
1539 ERL_DRV_BUSY_MSGQ_READ_ONLY, the currently used limit is read
1540 and written back to the integer variable. A new limit can be set
1541 by passing a pointer to an integer variable containing a valid
1542 limit. The passed value is written to the internal limit. The
1543 internal limit is then adjusted. After this the adjusted limit
1544 is written back to the integer variable from which the new value
1545 was read. Values are in bytes.
1546 The busy message queue feature can be disabled either by setting
1548 the ERL_DRV_FLAG_NO_BUSY_MSGQ driver flag in the driver_entry
1549 used by the driver, or by calling this function with
1550 ERL_DRV_BUSY_MSGQ_DISABLED as a limit (either low or high). When
1551 this feature has been disabled, it cannot be enabled again. When
1552 reading the limits, both are ERL_DRV_BUSY_MSGQ_DISABLED if this
1553 feature has been disabled.
1554 Processes sending command data to the port are suspended if
1556 either the port is busy or if the port message queue is busy.
1557 Suspended processes are resumed when neither the port or the
1558 port message queue is busy.
1559 For information about busy port functionality, see
1561 set_busy_port.
1562 void erl_drv_cond_broadcast(ErlDrvCond
1564 *cnd)
1565 Broadcasts on a condition variable. That is, if other threads
1567 are waiting on the condition variable being broadcast on, all of
1568 them are woken.
1569 cnd is a pointer to a condition variable to broadcast on.
1571 This function is thread-safe.
1573 ErlDrvCond *erl_drv_cond_create(char
1575 *name)
1576 Creates a condition variable and returns a pointer to it.
1578 name is a string identifying the created condition variable. It
1580 is used to identify the condition variable in planned future
1581 debug functionality.
1582 Returns NULL on failure. The driver creating the condition vari‐
1584 able is responsible for destroying it before the driver is
1585 unloaded.
1586 This function is thread-safe.
1588 void erl_drv_cond_destroy(ErlDrvCond
1590 *cnd)
1591 Destroys a condition variable previously created by
1593 erl_drv_cond_create.
1594 cnd is a pointer to a condition variable to destroy.
1596 This function is thread-safe.
1598 char *erl_drv_cond_name(ErlDrvCond
1600 *cnd)
1601 Returns a pointer to the name of the condition.
1603 cnd is a pointer to an initialized condition.
1605 Note:
1607 This function is intended for debugging purposes only.
1608 void erl_drv_cond_signal(ErlDrvCond
1611 *cnd)
1612 Signals on a condition variable. That is, if other threads are
1614 waiting on the condition variable being signaled, one of them is
1615 woken.
1616 cnd is a pointer to a condition variable to signal on.
1618 This function is thread-safe.
1620 void erl_drv_cond_wait(ErlDrvCond *cnd,
1622 ErlDrvMutex *mtx)
1623 Waits on a condition variable. The calling thread is blocked
1625 until another thread wakes it by signaling or broadcasting on
1626 the condition variable. Before the calling thread is blocked, it
1627 unlocks the mutex passed as argument. When the calling thread is
1628 woken, it locks the same mutex before returning. That is, the
1629 mutex currently must be locked by the calling thread when call‐
1630 ing this function.
1631 cnd is a pointer to a condition variable to wait on. mtx is a
1633 pointer to a mutex to unlock while waiting.
1634 Note:
1636 erl_drv_cond_wait can return even if no one has signaled or
1637 broadcast on the condition variable. Code calling
1638 erl_drv_cond_wait is always to be prepared for erl_drv_cond_wait
1639 returning even if the condition that the thread was waiting for
1640 has not occurred. That is, when returning from
1641 erl_drv_cond_wait, always check if the condition has occurred,
1642 and if not call erl_drv_cond_wait again.
1643 This function is thread-safe.
1646 int erl_drv_consume_timeslice(ErlDrvPort port,
1648 int percent)
1649 Gives the runtime system a hint about how much CPU time the cur‐
1651 rent driver callback call has consumed since the last hint, or
1652 since the the start of the callback if no previous hint has been
1653 given.
1654 port:
1656 Port handle of the executing port.
1657 percent:
1659 Approximate consumed fraction of a full time-slice in per‐
1660 cent.
1661 The time is specified as a fraction, in percent, of a full time-
1663 slice that a port is allowed to execute before it is to surren‐
1664 der the CPU to other runnable ports or processes. Valid range is
1665 [1, 100]. The scheduling time-slice is not an exact entity, but
1666 can usually be approximated to about 1 millisecond.
1667 Notice that it is up to the runtime system to determine if and
1669 how to use this information. Implementations on some platforms
1670 can use other means to determine the consumed fraction of the
1671 time-slice. Lengthy driver callbacks should, regardless of this,
1672 frequently call this function to determine if it is allowed to
1673 continue execution or not.
1674 This function returns a non-zero value if the time-slice has
1676 been exhausted, and zero if the callback is allowed to continue
1677 execution. If a non-zero value is returned, the driver callback
1678 is to return as soon as possible in order for the port to be
1679 able to yield.
1680 This function is provided to better support co-operative sched‐
1682 uling, improve system responsiveness, and to make it easier to
1683 prevent misbehaviors of the VM because of a port monopolizing a
1684 scheduler thread. It can be used when dividing lengthy work into
1685 some repeated driver callback calls, without the need to use
1686 threads.
1687 See also the important warning text at the beginning of this
1689 manual page.
1690 ErlDrvTime erl_drv_convert_time_unit(ErlDrvTime
1692 val, ErlDrvTimeUnit from, ErlDrvTimeUnit to)
1693 Converts the val value of time unit from to the corresponding
1695 value of time unit to. The result is rounded using the floor
1696 function.
1697 val:
1699 Value to convert time unit for.
1700 from:
1702 Time unit of val.
1703 to:
1705 Time unit of returned value.
1706 Returns ERL_DRV_TIME_ERROR if called with an invalid time unit
1708 argument.
1709 See also ErlDrvTime and ErlDrvTimeUnit.
1711 int erl_drv_equal_tids(ErlDrvTid tid1,
1713 ErlDrvTid tid2)
1714 Compares two thread identifiers, tid1 and tid2, for equality.
1716 Returns 0 it they are not equal, and a value not equal to 0 if
1718 they are equal.
1719 Note:
1721 A thread identifier can be reused very quickly after a thread
1722 has terminated. Therefore, if a thread corresponding to one of
1723 the involved thread identifiers has terminated since the thread
1724 identifier was saved, the result of erl_drv_equal_tids does pos‐
1725 sibly not give the expected result.
1726 This function is thread-safe.
1729 int erl_drv_getenv(const char *key, char
1731 *value, size_t *value_size)
1732 Retrieves the value of an environment variable.
1734 key:
1736 A NULL-terminated string containing the name of the environ‐
1737 ment variable.
1738 value:
1740 A pointer to an output buffer.
1741 value_size:
1743 A pointer to an integer. The integer is used both for pass‐
1744 ing input and output sizes (see below).
1745 When this function is called, *value_size is to contain the size
1747 of the value buffer.
1748 On success, 0 is returned, the value of the environment variable
1750 has been written to the value buffer, and *value_size contains
1751 the string length (excluding the terminating NULL character) of
1752 the value written to the value buffer.
1753 On failure, that is, no such environment variable was found, a
1755 value < 0 is returned. When the size of the value buffer is too
1756 small, a value > 0 is returned and *value_size has been set to
1757 the buffer size needed.
1758 Warning:
1760 This function reads the emulated environment used by os:getenv/1
1761 and not the environment used by libc's getenv(3) or similar.
1762 Drivers that require that these are in sync will need to do so
1763 themselves, but keep in mind that they are segregated for a rea‐
1764 son; getenv(3) and its friends are not thread-safe and may cause
1765 unrelated code to misbehave or crash the emulator.
1766 This function is thread-safe.
1769 void erl_drv_init_ack(ErlDrvPort port,
1771 ErlDrvData res)
1772 Acknowledges the start of the port.
1774 port:
1776 The port handle of the port (driver instance) doing the
1777 acknowledgment.
1778 res:
1780 The result of the port initialization. Can be the same val‐
1781 ues as the return value of start, that is, any of the error
1782 codes or the ErlDrvData that is to be used for this port.
1783 When this function is called the initiating erlang:open_port
1785 call is returned as if the start function had just been called.
1786 It can only be used when flag ERL_DRV_FLAG_USE_INIT_ACK has been
1787 set on the linked-in driver.
1788 ErlDrvTime erl_drv_monotonic_time(ErlDrvTimeUnit time_unit)
1790 Returns Erlang monotonic time. Notice that negative values are
1792 not uncommon.
1793 time_unit is time unit of returned value.
1795 Returns ERL_DRV_TIME_ERROR if called with an invalid time unit
1797 argument, or if called from a thread that is not a scheduler
1798 thread.
1799 See also ErlDrvTime and ErlDrvTimeUnit.
1801 ErlDrvMutex *erl_drv_mutex_create(char
1803 *name)
1804 Creates a mutex and returns a pointer to it.
1806 name is a string identifying the created mutex. It is used to
1808 identify the mutex in debug functionality (see note).
1809 Returns NULL on failure. The driver creating the mutex is
1811 responsible for destroying it before the driver is unloaded.
1812 This function is thread-safe.
1814 Note:
1816 One such debug functionality is the lock checker, which can
1817 detect locking order violations and thereby potential deadlock
1818 bugs. For the lock checker to work the name should be on the
1819 format "App.Type" or "App.Type[Instance]", where App is the name
1820 of the application, Type is the name of the lock type and
1821 Instance is optional information about each lock instance.
1822 "App.Type" should be a unique name for the lock checker to
1823 detect lock order violations between locks of different types.
1824 The Instance information is currently ignored.
1825 For example, if we have mutexes of types "myapp.xtable" and
1827 "myapp.xitem" then the lock checker will make sure either
1828 "myapp.xtable" locks are never locked after "myapp.xitem" locks
1829 or vice versa.
1830 void erl_drv_mutex_destroy(ErlDrvMutex
1833 *mtx)
1834 Destroys a mutex previously created by erl_drv_mutex_create. The
1836 mutex must be in an unlocked state before it is destroyed.
1837 mtx is a pointer to a mutex to destroy.
1839 This function is thread-safe.
1841 void erl_drv_mutex_lock(ErlDrvMutex
1843 *mtx)
1844 Locks a mutex. The calling thread is blocked until the mutex has
1846 been locked. A thread that has currently locked the mutex cannot
1847 lock the same mutex again.
1848 mtx is a pointer to a mutex to lock.
1850 Warning:
1852 If you leave a mutex locked in an emulator thread when you let
1853 the thread out of your control, you will very likely deadlock
1854 the whole emulator.
1855 This function is thread-safe.
1858 char *erl_drv_mutex_name(ErlDrvMutex
1860 *mtx)
1861 Returns a pointer to the mutex name.
1863 mtx is a pointer to an initialized mutex.
1865 Note:
1867 This function is intended for debugging purposes only.
1868 int erl_drv_mutex_trylock(ErlDrvMutex
1871 *mtx)
1872 Tries to lock a mutex. A thread that has currently locked the
1874 mutex cannot try to lock the same mutex again.
1875 mtx is a pointer to a mutex to try to lock.
1877 Returns 0 on success, otherwise EBUSY.
1879 Warning:
1881 If you leave a mutex locked in an emulator thread when you let
1882 the thread out of your control, you will very likely deadlock
1883 the whole emulator.
1884 This function is thread-safe.
1887 void erl_drv_mutex_unlock(ErlDrvMutex
1889 *mtx)
1890 Unlocks a mutex. The mutex currently must be locked by the call‐
1892 ing thread.
1893 mtx is a pointer to a mutex to unlock.
1895 This function is thread-safe.
1897 int erl_drv_output_term(ErlDrvTermData port,
1899 ErlDrvTermData* term, int n)
1900 Sends data in the special driver term format to the port owner
1902 process. This is a fast way to deliver term data from a driver.
1903 It needs no binary conversion, so the port owner process
1904 receives data as normal Erlang terms. The erl_drv_send_term
1905 functions can be used for sending to any process on the local
1906 node.
1907 Note:
1909 Parameter port is not an ordinary port handle, but a port handle
1910 converted using driver_mk_port.
1911 Parameter term points to an array of ErlDrvTermData with n ele‐
1914 ments. This array contains terms described in the driver term
1915 format. Every term consists of 1-4 elements in the array. The
1916 first term has a term type and then arguments. Parameter port
1917 specifies the sending port.
1918 Tuples, maps, and lists (except strings, see below) are built in
1920 reverse polish notation, so that to build a tuple, the elements
1921 are specified first, and then the tuple term, with a count.
1922 Likewise for lists and maps.
1923 * A tuple must be specified with the number of elements. (The
1925 elements precede the ERL_DRV_TUPLE term.)
1926 * A map must be specified with the number of key-value pairs
1928 N. The key-value pairs must precede the ERL_DRV_MAP in this
1929 order: key1,value1,key2,value2,...,keyN,valueN. Duplicate
1930 keys are not allowed.
1931 * A list must be specified with the number of elements,
1933 including the tail, which is the last term preceding
1934 ERL_DRV_LIST.
1935 The special term ERL_DRV_STRING_CONS is used to "splice" in a
1937 string in a list, a string specified this way is not a list in
1938 itself, but the elements are elements of the surrounding list.
1939 Term type Arguments
1941 --------- ---------
1942 ERL_DRV_NIL
1943 ERL_DRV_ATOM ErlDrvTermData atom (from driver_mk_atom(char *string))
1944 ERL_DRV_INT ErlDrvSInt integer
1945 ERL_DRV_UINT ErlDrvUInt integer
1946 ERL_DRV_INT64 ErlDrvSInt64 *integer_ptr
1947 ERL_DRV_UINT64 ErlDrvUInt64 *integer_ptr
1948 ERL_DRV_PORT ErlDrvTermData port (from driver_mk_port(ErlDrvPort port))
1949 ERL_DRV_BINARY ErlDrvBinary *bin, ErlDrvUInt len, ErlDrvUInt offset
1950 ERL_DRV_BUF2BINARY char *buf, ErlDrvUInt len
1951 ERL_DRV_STRING char *str, int len
1952 ERL_DRV_TUPLE int sz
1953 ERL_DRV_LIST int sz
1954 ERL_DRV_PID ErlDrvTermData pid (from driver_connected(ErlDrvPort port)
1955 or driver_caller(ErlDrvPort port))
1956 ERL_DRV_STRING_CONS char *str, int len
1957 ERL_DRV_FLOAT double *dbl
1958 ERL_DRV_EXT2TERM char *buf, ErlDrvUInt len
1959 ERL_DRV_MAP int sz
1960 The unsigned integer data type ErlDrvUInt and the signed integer
1962 data type ErlDrvSInt are 64 bits wide on a 64-bit runtime system
1963 and 32 bits wide on a 32-bit runtime system. They were intro‐
1964 duced in ERTS 5.6 and replaced some of the int arguments in the
1965 list above.
1966 The unsigned integer data type ErlDrvUInt64 and the signed inte‐
1968 ger data type ErlDrvSInt64 are always 64 bits wide. They were
1969 introduced in ERTS 5.7.4.
1970 To build the tuple {tcp, Port, [100 | Binary]}, the following
1972 call can be made.
1973 ErlDrvBinary* bin = ...
1975 ErlDrvPort port = ...
1976 ErlDrvTermData spec[] = {
1977 ERL_DRV_ATOM, driver_mk_atom("tcp"),
1978 ERL_DRV_PORT, driver_mk_port(drvport),
1979 ERL_DRV_INT, 100,
1980 ERL_DRV_BINARY, bin, 50, 0,
1981 ERL_DRV_LIST, 2,
1982 ERL_DRV_TUPLE, 3,
1983 };
1984 erl_drv_output_term(driver_mk_port(drvport), spec, sizeof(spec) / sizeof(spec[0]));
1985 Here bin is a driver binary of length at least 50 and drvport is
1987 a port handle. Notice that ERL_DRV_LIST comes after the elements
1988 of the list, likewise ERL_DRV_TUPLE.
1989 The ERL_DRV_STRING_CONS term is a way to construct strings. It
1991 works differently from how ERL_DRV_STRING works.
1992 ERL_DRV_STRING_CONS builds a string list in reverse order (as
1993 opposed to how ERL_DRV_LIST works), concatenating the strings
1994 added to a list. The tail must be specified before
1995 ERL_DRV_STRING_CONS.
1996 ERL_DRV_STRING constructs a string, and ends it. (So it is the
1998 same as ERL_DRV_NIL followed by ERL_DRV_STRING_CONS.)
1999 /* to send [x, "abc", y] to the port: */
2001 ErlDrvTermData spec[] = {
2002 ERL_DRV_ATOM, driver_mk_atom("x"),
2003 ERL_DRV_STRING, (ErlDrvTermData)"abc", 3,
2004 ERL_DRV_ATOM, driver_mk_atom("y"),
2005 ERL_DRV_NIL,
2006 ERL_DRV_LIST, 4
2007 };
2008 erl_drv_output_term(driver_mk_port(drvport), spec, sizeof(spec) / sizeof(spec[0]));
2009 /* to send "abc123" to the port: */
2011 ErlDrvTermData spec[] = {
2012 ERL_DRV_NIL, /* with STRING_CONS, the tail comes first */
2013 ERL_DRV_STRING_CONS, (ErlDrvTermData)"123", 3,
2014 ERL_DRV_STRING_CONS, (ErlDrvTermData)"abc", 3,
2015 };
2016 erl_drv_output_term(driver_mk_port(drvport), spec, sizeof(spec) / sizeof(spec[0]));
2017 The ERL_DRV_EXT2TERM term type is used for passing a term
2019 encoded with the external format, that is, a term that has been
2020 encoded by erlang:term_to_binary, erl_interface:ei(3), and so
2021 on. For example, if binp is a pointer to an ErlDrvBinary that
2022 contains term {17, 4711} encoded with the external format, and
2023 you want to wrap it in a two-tuple with the tag my_tag, that is,
2024 {my_tag, {17, 4711}}, you can do as follows:
2025 ErlDrvTermData spec[] = {
2027 ERL_DRV_ATOM, driver_mk_atom("my_tag"),
2028 ERL_DRV_EXT2TERM, (ErlDrvTermData) binp->orig_bytes, binp->orig_size
2029 ERL_DRV_TUPLE, 2,
2030 };
2031 erl_drv_output_term(driver_mk_port(drvport), spec, sizeof(spec) / sizeof(spec[0]));
2032 To build the map #{key1 => 100, key2 => {200, 300}}, the follow‐
2034 ing call can be made.
2035 ErlDrvPort port = ...
2037 ErlDrvTermData spec[] = {
2038 ERL_DRV_ATOM, driver_mk_atom("key1"),
2039 ERL_DRV_INT, 100,
2040 ERL_DRV_ATOM, driver_mk_atom("key2"),
2041 ERL_DRV_INT, 200,
2042 ERL_DRV_INT, 300,
2043 ERL_DRV_TUPLE, 2,
2044 ERL_DRV_MAP, 2
2045 };
2046 erl_drv_output_term(driver_mk_port(drvport), spec, sizeof(spec) / sizeof(spec[0]));
2047 If you want to pass a binary and do not already have the content
2049 of the binary in an ErlDrvBinary, you can benefit from using
2050 ERL_DRV_BUF2BINARY instead of creating an ErlDrvBinary through
2051 driver_alloc_binary and then pass the binary through
2052 ERL_DRV_BINARY. The runtime system often allocates binaries
2053 smarter if ERL_DRV_BUF2BINARY is used. However, if the content
2054 of the binary to pass already resides in an ErlDrvBinary, it is
2055 normally better to pass the binary using ERL_DRV_BINARY and the
2056 ErlDrvBinary in question.
2057 The ERL_DRV_UINT, ERL_DRV_BUF2BINARY, and ERL_DRV_EXT2TERM term
2059 types were introduced in ERTS 5.6.
2060 This function is only thread-safe when the emulator with SMP
2062 support is used.
2063 int erl_drv_putenv(const char *key, char
2065 *value)
2066 Sets the value of an environment variable.
2068 key is a NULL-terminated string containing the name of the envi‐
2070 ronment variable.
2071 value is a NULL-terminated string containing the new value of
2073 the environment variable.
2074 Returns 0 on success, otherwise a value != 0.
2076 Note:
2078 The result of passing the empty string ("") as a value is plat‐
2079 form-dependent. On some platforms the variable value is set to
2080 the empty string, on others the environment variable is removed.
2081 Warning:
2084 This function modifies the emulated environment used by
2085 os:putenv/2 and not the environment used by libc's putenv(3) or
2086 similar. Drivers that require that these are in sync will need
2087 to do so themselves, but keep in mind that they are segregated
2088 for a reason; putenv(3) and its friends are not thread-safe and
2089 may cause unrelated code to misbehave or crash the emulator.
2090 This function is thread-safe.
2093 ErlDrvRWLock *erl_drv_rwlock_create(char
2095 *name)
2096 Creates an rwlock and returns a pointer to it.
2098 name is a string identifying the created rwlock. It is used to
2100 identify the rwlock in debug functionality (see note about the
2101 lock checker).
2102 Returns NULL on failure. The driver creating the rwlock is
2104 responsible for destroying it before the driver is unloaded.
2105 This function is thread-safe.
2107 void erl_drv_rwlock_destroy(ErlDrvRWLock
2109 *rwlck)
2110 Destroys an rwlock previously created by erl_drv_rwlock_create.
2112 The rwlock must be in an unlocked state before it is destroyed.
2113 rwlck is a pointer to an rwlock to destroy.
2115 This function is thread-safe.
2117 char *erl_drv_rwlock_name(ErlDrvRWLock
2119 *rwlck)
2120 Returns a pointer to the name of the rwlock.
2122 rwlck is a pointer to an initialized rwlock.
2124 Note:
2126 This function is intended for debugging purposes only.
2127 void erl_drv_rwlock_rlock(ErlDrvRWLock
2130 *rwlck)
2131 Read locks an rwlock. The calling thread is blocked until the
2133 rwlock has been read locked. A thread that currently has read or
2134 read/write locked the rwlock cannot lock the same rwlock again.
2135 rwlck is a pointer to the rwlock to read lock.
2137 Warning:
2139 If you leave an rwlock locked in an emulator thread when you let
2140 the thread out of your control, you will very likely deadlock
2141 the whole emulator.
2142 This function is thread-safe.
2145 void erl_drv_rwlock_runlock(ErlDrvRWLock
2147 *rwlck)
2148 Read unlocks an rwlock. The rwlock currently must be read locked
2150 by the calling thread.
2151 rwlck is a pointer to an rwlock to read unlock.
2153 This function is thread-safe.
2155 void erl_drv_rwlock_rwlock(ErlDrvRWLock
2157 *rwlck)
2158 Read/write locks an rwlock. The calling thread is blocked until
2160 the rwlock has been read/write locked. A thread that currently
2161 has read or read/write locked the rwlock cannot lock the same
2162 rwlock again.
2163 rwlck is a pointer to an rwlock to read/write lock.
2165 Warning:
2167 If you leave an rwlock locked in an emulator thread when you let
2168 the thread out of your control, you will very likely deadlock
2169 the whole emulator.
2170 This function is thread-safe.
2173 void erl_drv_rwlock_rwunlock(ErlDrvRWLock
2175 *rwlck)
2176 Read/write unlocks an rwlock. The rwlock currently must be
2178 read/write locked by the calling thread.
2179 rwlck is a pointer to an rwlock to read/write unlock.
2181 This function is thread-safe.
2183 int erl_drv_rwlock_tryrlock(ErlDrvRWLock
2185 *rwlck)
2186 Tries to read lock an rwlock.
2188 rwlck is a pointer to an rwlock to try to read lock.
2190 Returns 0 on success, otherwise EBUSY. A thread that currently
2192 has read or read/write locked the rwlock cannot try to lock the
2193 same rwlock again.
2194 Warning:
2196 If you leave an rwlock locked in an emulator thread when you let
2197 the thread out of your control, you will very likely deadlock
2198 the whole emulator.
2199 This function is thread-safe.
2202 int erl_drv_rwlock_tryrwlock(ErlDrvRWLock
2204 *rwlck)
2205 Tries to read/write lock an rwlock. A thread that currently has
2207 read or read/write locked the rwlock cannot try to lock the same
2208 rwlock again.
2209 rwlckis pointer to an rwlock to try to read/write lock.
2211 Returns 0 on success, otherwise EBUSY.
2213 Warning:
2215 If you leave an rwlock locked in an emulator thread when you let
2216 the thread out of your control, you will very likely deadlock
2217 the whole emulator.
2218 This function is thread-safe.
2221 int erl_drv_send_term(ErlDrvTermData port,
2223 ErlDrvTermData receiver, ErlDrvTermData* term, int n)
2224 This function is the only way for a driver to send data to other
2226 processes than the port owner process. Parameter receiver speci‐
2227 fies the process to receive the data.
2228 Note:
2230 Parameter port is not an ordinary port handle, but a port handle
2231 converted using driver_mk_port.
2232 Parameters port, term, and n work as in erl_drv_output_term.
2235 This function is only thread-safe when the emulator with SMP
2237 support is used.
2238 void erl_drv_set_os_pid(ErlDrvPort port,
2240 ErlDrvSInt pid)
2241 Sets the os_pid seen when doing erlang:port_info/2 on this port.
2243 port is the port handle of the port (driver instance) to set the
2245 pid on. pidis the pid to set.
2246 int erl_drv_thread_create(char *name, ErlDrvTid
2248 *tid, void * (*func)(void *), void *arg, ErlDrvThreadOpts
2249 *opts)
2250 Creates a new thread.
2252 name:
2254 A string identifying the created thread. It is used to iden‐
2255 tify the thread in planned future debug functionality.
2256 tid:
2258 A pointer to a thread identifier variable.
2259 func:
2261 A pointer to a function to execute in the created thread.
2262 arg:
2264 A pointer to argument to the func function.
2265 opts:
2267 A pointer to thread options to use or NULL.
2268 Returns 0 on success, otherwise an errno value is returned to
2270 indicate the error. The newly created thread begins executing in
2271 the function pointed to by func, and func is passed arg as argu‐
2272 ment. When erl_drv_thread_create returns, the thread identifier
2273 of the newly created thread is available in *tid. opts can be
2274 either a NULL pointer, or a pointer to an ErlDrvThreadOpts
2275 structure. If opts is a NULL pointer, default options are used,
2276 otherwise the passed options are used.
2277 Warning:
2279 You are not allowed to allocate the ErlDrvThreadOpts structure
2280 by yourself. It must be allocated and initialized by
2281 erl_drv_thread_opts_create.
2282 The created thread terminates either when func returns or if
2285 erl_drv_thread_exit is called by the thread. The exit value of
2286 the thread is either returned from func or passed as argument to
2287 erl_drv_thread_exit. The driver creating the thread is responsi‐
2288 ble for joining the thread, through erl_drv_thread_join, before
2289 the driver is unloaded. "Detached" threads cannot be created,
2290 that is, threads that do not need to be joined.
2291 Warning:
2293 All created threads must be joined by the driver before it is
2294 unloaded. If the driver fails to join all threads created before
2295 it is unloaded, the runtime system most likely crashes when the
2296 driver code is unloaded.
2297 This function is thread-safe.
2300 void erl_drv_thread_exit(void
2302 *exit_value)
2303 Terminates the calling thread with the exit value passed as
2305 argument. exit_value is a pointer to an exit value or NULL.
2306 You are only allowed to terminate threads created with
2308 erl_drv_thread_create.
2309 The exit value can later be retrieved by another thread through
2311 erl_drv_thread_join.
2312 This function is thread-safe.
2314 int erl_drv_thread_join(ErlDrvTid tid, void
2316 **exit_value)
2317 Joins the calling thread with another thread, that is, the call‐
2319 ing thread is blocked until the thread identified by tid has
2320 terminated.
2321 tid is the thread identifier of the thread to join. exit_value
2323 is a pointer to a pointer to an exit value, or NULL.
2324 Returns 0 on success, otherwise an errno value is returned to
2326 indicate the error.
2327 A thread can only be joined once. The behavior of joining more
2329 than once is undefined, an emulator crash is likely. If
2330 exit_value == NULL, the exit value of the terminated thread is
2331 ignored, otherwise the exit value of the terminated thread is
2332 stored at *exit_value.
2333 This function is thread-safe.
2335 char *erl_drv_thread_name(ErlDrvTid
2337 tid)
2338 Returns a pointer to the name of the thread.
2340 tid is a thread identifier.
2342 Note:
2344 This function is intended for debugging purposes only.
2345 ErlDrvThreadOpts *erl_drv_thread_opts_create(char *name)
2348 Allocates and initializes a thread option structure.
2350 name is a string identifying the created thread options. It is
2352 used to identify the thread options in planned future debug
2353 functionality.
2354 Returns NULL on failure. A thread option structure is used for
2356 passing options to erl_drv_thread_create. If the structure is
2357 not modified before it is passed to erl_drv_thread_create, the
2358 default values are used.
2359 Warning:
2361 You are not allowed to allocate the ErlDrvThreadOpts structure
2362 by yourself. It must be allocated and initialized by
2363 erl_drv_thread_opts_create.
2364 This function is thread-safe.
2367 void erl_drv_thread_opts_destroy(ErlDrvThreadOpts *opts)
2369 Destroys thread options previously created by
2371 erl_drv_thread_opts_create.
2372 opts is a pointer to thread options to destroy.
2374 This function is thread-safe.
2376 ErlDrvTid erl_drv_thread_self(void)
2378 Returns the thread identifier of the calling thread.
2380 This function is thread-safe.
2382 ErlDrvTime erl_drv_time_offset(ErlDrvTimeUnit
2384 time_unit)
2385 Returns the current time offset between Erlang monotonic time
2387 and Erlang system time converted into the time_unit passed as
2388 argument.
2389 time_unit is time unit of returned value.
2391 Returns ERL_DRV_TIME_ERROR if called with an invalid time unit
2393 argument, or if called from a thread that is not a scheduler
2394 thread.
2395 See also ErlDrvTime and ErlDrvTimeUnit.
2397 void *erl_drv_tsd_get(ErlDrvTSDKey
2399 key)
2400 Returns the thread-specific data associated with key for the
2402 calling thread.
2403 key is a thread-specific data key.
2405 Returns NULL if no data has been associated with key for the
2407 calling thread.
2408 This function is thread-safe.
2410 int erl_drv_tsd_key_create(char *name,
2412 ErlDrvTSDKey *key)
2413 Creates a thread-specific data key.
2415 name is a string identifying the created key. It is used to
2417 identify the key in planned future debug functionality.
2418 key is a pointer to a thread-specific data key variable.
2420 Returns 0 on success, otherwise an errno value is returned to
2422 indicate the error. The driver creating the key is responsible
2423 for destroying it before the driver is unloaded.
2424 This function is thread-safe.
2426 void erl_drv_tsd_key_destroy(ErlDrvTSDKey
2428 key)
2429 Destroys a thread-specific data key previously created by
2431 erl_drv_tsd_key_create. All thread-specific data using this key
2432 in all threads must be cleared (see erl_drv_tsd_set) before the
2433 call to erl_drv_tsd_key_destroy.
2434 key is a thread-specific data key to destroy.
2436 Warning:
2438 A destroyed key is very likely to be reused soon. Therefore, if
2439 you fail to clear the thread-specific data using this key in a
2440 thread before destroying the key, you will very likely get unex‐
2441 pected errors in other parts of the system.
2442 This function is thread-safe.
2445 void erl_drv_tsd_set(ErlDrvTSDKey key, void
2447 *data)
2448 Sets thread-specific data associated with key for the calling
2450 thread. You are only allowed to set thread-specific data for
2451 threads while they are fully under your control. For example, if
2452 you set thread-specific data in a thread calling a driver call‐
2453 back function, it must be cleared, that is, set to NULL, before
2454 returning from the driver callback function.
2455 key is a thread-specific data key.
2457 data is a pointer to data to associate with key in the calling
2459 thread.
2460 Warning:
2462 If you fail to clear thread-specific data in an emulator thread
2463 before letting it out of your control, you might never be able
2464 to clear this data with later unexpected errors in other parts
2465 of the system as a result.
2466 This function is thread-safe.
2469 char *erl_errno_id(int error)
2471 Returns the atom name of the Erlang error, given the error num‐
2473 ber in error. The error atoms are einval, enoent, and so on. It
2474 can be used to make error terms from the driver.
2475 int remove_driver_entry(ErlDrvEntry
2477 *de)
2478 Removes a driver entry de previously added with
2480 add_driver_entry.
2481 Driver entries added by the erl_ddll Erlang interface cannot be
2483 removed by using this interface.
2484 void set_busy_port(ErlDrvPort port, int
2486 on)
2487 Sets and unsets the busy state of the port. If on is non-zero,
2489 the port is set to busy. If it is zero, the port is set to not
2490 busy. You typically want to combine this feature with the busy
2491 port message queue functionality.
2492 Processes sending command data to the port are suspended if
2494 either the port or the port message queue is busy. Suspended
2495 processes are resumed when neither the port or the port message
2496 queue is busy. Command data is in this context data passed to
2497 the port using either Port ! {Owner, {command, Data}} or
2498 port_command/[2,3].
2499 If the ERL_DRV_FLAG_SOFT_BUSY has been set in the driver_entry,
2501 data can be forced into the driver through erlang:port_com‐
2502 mand(Port, Data, [force]) even if the driver has signaled that
2503 it is busy.
2504 For information about busy port message queue functionality, see
2506 erl_drv_busy_msgq_limits.
2507 void set_port_control_flags(ErlDrvPort port,
2509 int flags)
2510 Sets flags for how the control driver entry function will return
2512 data to the port owner process. (The control function is called
2513 from erlang:port_control/3.)
2514 Currently there are only two meaningful values for flags: 0
2516 means that data is returned in a list, and PORT_CON‐
2517 TROL_FLAG_BINARY means data is returned as a binary from con‐
2518 trol.
2519
2521 driver_entry(3), erlang(3), erl_ddll(3), section How to Implement an
2522 Alternative Carrier for the Erlang Distribution in the User's Guide
2523Ericsson AB erts 10.7.1 erl_driver(3)