1TALLOC(3) [FIXME: manual] TALLOC(3)
2
6 talloc - hierarchical reference counted memory pool system with
7 destructors
8
10 #include <talloc/talloc.h>
11
13 If you are used to talloc from Samba3 then please read this carefully,
14 as talloc has changed a lot.
15 The new talloc is a hierarchical, reference counted memory pool system
17 with destructors. Quite a mouthful really, but not too bad once you get
18 used to it.
19 Perhaps the biggest change from Samba3 is that there is no distinction
21 between a "talloc context" and a "talloc pointer". Any pointer returned
22 from talloc() is itself a valid talloc context. This means you can do
23 this:
24 struct foo *X = talloc(mem_ctx, struct foo);
26 X->name = talloc_strdup(X, "foo");
27 and the pointer X->name would be a "child" of the talloc context X
30 which is itself a child of mem_ctx. So if you do talloc_free(mem_ctx)
31 then it is all destroyed, whereas if you do talloc_free(X) then just X
32 and X->name are destroyed, and if you do talloc_free(X->name) then just
33 the name element of X is destroyed.
34 If you think about this, then what this effectively gives you is an
36 n-ary tree, where you can free any part of the tree with talloc_free().
37 If you find this confusing, then I suggest you run the testsuite
39 program to watch talloc in action. You may also like to add your own
40 tests to testsuite.c to clarify how some particular situation is
41 handled.
42
44 The following is a complete guide to the talloc API. Read it all at
45 least twice.
46 (type *)talloc(const void *ctx, type);
48 The talloc() macro is the core of the talloc library. It takes a memory
49 ctx and a type, and returns a pointer to a new area of memory of the
50 given type.
51 The returned pointer is itself a talloc context, so you can use it as
53 the ctx argument to more calls to talloc() if you wish.
54 The returned pointer is a "child" of the supplied context. This means
56 that if you talloc_free() the ctx then the new child disappears as
57 well. Alternatively you can free just the child.
58 The ctx argument to talloc() can be NULL, in which case a new top level
60 context is created.
61 void *talloc_size(const void *ctx, size_t size);
63 The function talloc_size() should be used when you don´t have a
64 convenient type to pass to talloc(). Unlike talloc(), it is not type
65 safe (as it returns a void *), so you are on your own for type
66 checking.
67 (typeof(ptr)) talloc_ptrtype(const void *ctx, ptr);
69 The talloc_ptrtype() macro should be used when you have a pointer and
70 want to allocate memory to point at with this pointer. When compiling
71 with gcc >= 3 it is typesafe. Note this is a wrapper of talloc_size()
72 and talloc_get_name() will return the current location in the source
73 file. and not the type.
74 int talloc_free(void *ptr);
76 The talloc_free() function frees a piece of talloc memory, and all its
77 children. You can call talloc_free() on any pointer returned by
78 talloc().
79 The return value of talloc_free() indicates success or failure, with 0
81 returned for success and -1 for failure. The only possible failure
82 condition is if ptr had a destructor attached to it and the destructor
83 returned -1. See “talloc_set_destructor()” for details on destructors.
84 If this pointer has an additional parent when talloc_free() is called
86 then the memory is not actually released, but instead the most recently
87 established parent is destroyed. See “talloc_reference()” for details
88 on establishing additional parents.
89 For more control on which parent is removed, see “talloc_unlink()”.
91 talloc_free() operates recursively on its children.
93 From the 2.0 version of talloc, as a special case, talloc_free() is
95 refused on pointers that have more than one parent, as talloc would
96 have no way of knowing which parent should be removed. To free a
97 pointer that has more than one parent please use talloc_unlink().
98 To help you find problems in your code caused by this behaviour, if you
100 do try and free a pointer with more than one parent then the talloc
101 logging function will be called to give output like this:
102 ERROR: talloc_free with references at some_dir/source/foo.c:123
104 reference at some_dir/source/other.c:325
105 reference at some_dir/source/third.c:121
106 Please see the documentation for talloc_set_log_fn() and
109 talloc_set_log_stderr() for more information on talloc logging
110 functions.
111 void *talloc_reference(const void *ctx, const void *ptr);
113 The talloc_reference() function makes ctx an additional parent of ptr.
114 The return value of talloc_reference() is always the original pointer
116 ptr, unless talloc ran out of memory in creating the reference in which
117 case it will return NULL (each additional reference consumes around 48
118 bytes of memory on intel x86 platforms).
119 If ptr is NULL, then the function is a no-op, and simply returns NULL.
121 After creating a reference you can free it in one of the following
123 ways:
124 · you can talloc_free() any parent of the original pointer. That will
126 reduce the number of parents of this pointer by 1, and will cause
127 this pointer to be freed if it runs out of parents.
128 · you can talloc_free() the pointer itself. That will destroy the
130 most recently established parent to the pointer and leave the
131 pointer as a child of its current parent.
132 For more control on which parent to remove, see “talloc_unlink()”.
135 int talloc_unlink(const void *ctx, const void *ptr);
137 The talloc_unlink() function removes a specific parent from ptr. The
138 ctx passed must either be a context used in talloc_reference() with
139 this pointer, or must be a direct parent of ptr.
140 Note that if the parent has already been removed using talloc_free()
142 then this function will fail and will return -1. Likewise, if ptr is
143 NULL, then the function will make no modifications and return -1.
144 Usually you can just use talloc_free() instead of talloc_unlink(), but
146 sometimes it is useful to have the additional control on which parent
147 is removed.
148 void talloc_set_destructor(const void *ptr, int (*destructor)(void *));
150 The function talloc_set_destructor() sets the destructor for the
151 pointer ptr. A destructor is a function that is called when the memory
152 used by a pointer is about to be released. The destructor receives ptr
153 as an argument, and should return 0 for success and -1 for failure.
154 The destructor can do anything it wants to, including freeing other
156 pieces of memory. A common use for destructors is to clean up operating
157 system resources (such as open file descriptors) contained in the
158 structure the destructor is placed on.
159 You can only place one destructor on a pointer. If you need more than
161 one destructor then you can create a zero-length child of the pointer
162 and place an additional destructor on that.
163 To remove a destructor call talloc_set_destructor() with NULL for the
165 destructor.
166 If your destructor attempts to talloc_free() the pointer that it is the
168 destructor for then talloc_free() will return -1 and the free will be
169 ignored. This would be a pointless operation anyway, as the destructor
170 is only called when the memory is just about to go away.
171 int talloc_increase_ref_count(const void *ptr);
173 The talloc_increase_ref_count(ptr) function is exactly equivalent to:
174 talloc_reference(NULL, ptr);
176 You can use either syntax, depending on which you think is clearer in
178 your code.
179 It returns 0 on success and -1 on failure.
181 size_t talloc_reference_count(const void *ptr);
183 Return the number of references to the pointer.
184 void talloc_set_name(const void *ptr, const char *fmt, ...);
186 Each talloc pointer has a "name". The name is used principally for
187 debugging purposes, although it is also possible to set and get the
188 name on a pointer in as a way of "marking" pointers in your code.
189 The main use for names on pointer is for "talloc reports". See
191 “talloc_report_depth_cb()”, “talloc_report_depth_file()”,
192 “talloc_report()” “talloc_report()” and “talloc_report_full()” for
193 details. Also see “talloc_enable_leak_report()” and
194 “talloc_enable_leak_report_full()”.
195 The talloc_set_name() function allocates memory as a child of the
197 pointer. It is logically equivalent to:
198 talloc_set_name_const(ptr, talloc_asprintf(ptr, fmt, ...));
200 Note that multiple calls to talloc_set_name() will allocate more memory
202 without releasing the name. All of the memory is released when the ptr
203 is freed using talloc_free().
204 void talloc_set_name_const(const void *ptr, const char *name);
206 The function talloc_set_name_const() is just like talloc_set_name(),
207 but it takes a string constant, and is much faster. It is extensively
208 used by the "auto naming" macros, such as talloc_p().
209 This function does not allocate any memory. It just copies the supplied
211 pointer into the internal representation of the talloc ptr. This means
212 you must not pass a name pointer to memory that will disappear before
213 ptr is freed with talloc_free().
214 void *talloc_named(const void *ctx, size_t size, const char *fmt, ...);
216 The talloc_named() function creates a named talloc pointer. It is
217 equivalent to:
218 ptr = talloc_size(ctx, size);
220 talloc_set_name(ptr, fmt, ....);
221 void *talloc_named_const(const void *ctx, size_t size, const char *name);
223 This is equivalent to:
224 ptr = talloc_size(ctx, size);
226 talloc_set_name_const(ptr, name);
227 const char *talloc_get_name(const void *ptr);
229 This returns the current name for the given talloc pointer, ptr. See
230 “talloc_set_name()” for details.
231 void *talloc_init(const char *fmt, ...);
233 This function creates a zero length named talloc context as a top level
234 context. It is equivalent to:
235 talloc_named(NULL, 0, fmt, ...);
237 void *talloc_new(void *ctx);
239 This is a utility macro that creates a new memory context hanging off
240 an exiting context, automatically naming it "talloc_new: __location__"
241 where __location__ is the source line it is called from. It is
242 particularly useful for creating a new temporary working context.
243 (type *)talloc_realloc(const void *ctx, void *ptr, type, count);
245 The talloc_realloc() macro changes the size of a talloc pointer. It has
246 the following equivalences:
247 talloc_realloc(ctx, NULL, type, 1) ==> talloc(ctx, type);
249 talloc_realloc(ctx, ptr, type, 0) ==> talloc_free(ptr);
250 The ctx argument is only used if ptr is not NULL, otherwise it is
252 ignored.
253 talloc_realloc() returns the new pointer, or NULL on failure. The call
255 will fail either due to a lack of memory, or because the pointer has
256 more than one parent (see “talloc_reference()”).
257 void *talloc_realloc_size(const void *ctx, void *ptr, size_t size);
259 the talloc_realloc_size() function is useful when the type is not known
260 so the type-safe talloc_realloc() cannot be used.
261 TYPE *talloc_steal(const void *new_ctx, const TYPE *ptr);
263 The talloc_steal() function changes the parent context of a talloc
264 pointer. It is typically used when the context that the pointer is
265 currently a child of is going to be freed and you wish to keep the
266 memory for a longer time.
267 The talloc_steal() function returns the pointer that you pass it. It
269 does not have any failure modes.
270 It is possible to produce loops in the parent/child relationship if you
272 are not careful with talloc_steal(). No guarantees are provided as to
273 your sanity or the safety of your data if you do this.
274 Note that if you try and call talloc_steal() on a pointer that has more
276 than one parent then the result is ambiguous. Talloc will choose to
277 remove the parent that is currently indicated by talloc_parent() and
278 replace it with the chosen parent. You will also get a message like
279 this via the talloc logging functions:
280 WARNING: talloc_steal with references at some_dir/source/foo.c:123
282 reference at some_dir/source/other.c:325
283 reference at some_dir/source/third.c:121
284 To unambiguously change the parent of a pointer please see the function
287 “talloc_reparent()”. See the talloc_set_log_fn() documentation for more
288 information on talloc logging.
289 TYPE *talloc_reparent(const void *old_parent, const void *new_parent, const
291 TYPE *ptr);
292 The talloc_reparent() function changes the parent context of a talloc
293 pointer. It is typically used when the context that the pointer is
294 currently a child of is going to be freed and you wish to keep the
295 memory for a longer time.
296 The talloc_reparent() function returns the pointer that you pass it. It
298 does not have any failure modes.
299 The difference between talloc_reparent() and talloc_steal() is that
301 talloc_reparent() can specify which parent you wish to change. This is
302 useful when a pointer has multiple parents via references.
303 TYPE *talloc_move(const void *new_ctx, TYPE **ptr);
305 The talloc_move() function is a wrapper around talloc_steal() which
306 zeros the source pointer after the move. This avoids a potential source
307 of bugs where a programmer leaves a pointer in two structures, and uses
308 the pointer from the old structure after it has been moved to a new
309 one.
310 size_t talloc_total_size(const void *ptr);
312 The talloc_total_size() function returns the total size in bytes used
313 by this pointer and all child pointers. Mostly useful for debugging.
314 Passing NULL is allowed, but it will only give a meaningful result if
316 talloc_enable_leak_report() or talloc_enable_leak_report_full() has
317 been called.
318 size_t talloc_total_blocks(const void *ptr);
320 The talloc_total_blocks() function returns the total memory block count
321 used by this pointer and all child pointers. Mostly useful for
322 debugging.
323 Passing NULL is allowed, but it will only give a meaningful result if
325 talloc_enable_leak_report() or talloc_enable_leak_report_full() has
326 been called.
327 void talloc_report(const void *ptr, FILE *f);
329 The talloc_report() function prints a summary report of all memory used
330 by ptr. One line of report is printed for each immediate child of ptr,
331 showing the total memory and number of blocks used by that child.
332 You can pass NULL for the pointer, in which case a report is printed
334 for the top level memory context, but only if
335 talloc_enable_leak_report() or talloc_enable_leak_report_full() has
336 been called.
337 void talloc_report_full(const void *ptr, FILE *f);
339 This provides a more detailed report than talloc_report(). It will
340 recursively print the entire tree of memory referenced by the pointer.
341 References in the tree are shown by giving the name of the pointer that
342 is referenced.
343 You can pass NULL for the pointer, in which case a report is printed
345 for the top level memory context, but only if
346 talloc_enable_leak_report() or talloc_enable_leak_report_full() has
347 been called.
348 void talloc_report_depth_cb(const void *ptr, int depth, int max_depth,
351 void (*callback)(const void *ptr, int depth, int max_depth, int is_ref, void *priv),
352 void *priv);
353 This provides a more flexible reports than talloc_report(). It will
355 recursively call the callback for the entire tree of memory referenced
356 by the pointer. References in the tree are passed with is_ref = 1 and
357 the pointer that is referenced.
358 You can pass NULL for the pointer, in which case a report is printed
360 for the top level memory context, but only if
361 talloc_enable_leak_report() or talloc_enable_leak_report_full() has
362 been called.
363 The recursion is stopped when depth >= max_depth. max_depth = -1 means
365 only stop at leaf nodes.
366 void talloc_report_depth_file(const void *ptr, int depth,
369 int max_depth, FILE *f);
370 This provides a more flexible reports than talloc_report(). It will let
372 you specify the depth and max_depth.
373 void talloc_enable_leak_report(void);
375 This enables calling of talloc_report(NULL, stderr) when the program
376 exits. In Samba4 this is enabled by using the --leak-report command
377 line option.
378 For it to be useful, this function must be called before any other
380 talloc function as it establishes a "null context" that acts as the top
381 of the tree. If you don´t call this function first then passing NULL to
382 talloc_report() or talloc_report_full() won´t give you the full tree
383 printout.
384 Here is a typical talloc report:
386 talloc report on ´null_context´ (total 267 bytes in 15 blocks)
388 libcli/auth/spnego_parse.c:55 contains 31 bytes in 2 blocks
389 libcli/auth/spnego_parse.c:55 contains 31 bytes in 2 blocks
390 iconv(UTF8,CP850) contains 42 bytes in 2 blocks
391 libcli/auth/spnego_parse.c:55 contains 31 bytes in 2 blocks
392 iconv(CP850,UTF8) contains 42 bytes in 2 blocks
393 iconv(UTF8,UTF-16LE) contains 45 bytes in 2 blocks
394 iconv(UTF-16LE,UTF8) contains 45 bytes in 2 blocks
395 void talloc_enable_leak_report_full(void);
398 This enables calling of talloc_report_full(NULL, stderr) when the
399 program exits. In Samba4 this is enabled by using the
400 --leak-report-full command line option.
401 For it to be useful, this function must be called before any other
403 talloc function as it establishes a "null context" that acts as the top
404 of the tree. If you don´t call this function first then passing NULL to
405 talloc_report() or talloc_report_full() won´t give you the full tree
406 printout.
407 Here is a typical full report:
409 full talloc report on ´root´ (total 18 bytes in 8 blocks)
411 p1 contains 18 bytes in 7 blocks (ref 0)
412 r1 contains 13 bytes in 2 blocks (ref 0)
413 reference to: p2
414 p2 contains 1 bytes in 1 blocks (ref 1)
415 x3 contains 1 bytes in 1 blocks (ref 0)
416 x2 contains 1 bytes in 1 blocks (ref 0)
417 x1 contains 1 bytes in 1 blocks (ref 0)
418 (type *)talloc_zero(const void *ctx, type);
421 The talloc_zero() macro is equivalent to:
422 ptr = talloc(ctx, type);
424 if (ptr) memset(ptr, 0, sizeof(type));
425 void *talloc_zero_size(const void *ctx, size_t size)
427 The talloc_zero_size() function is useful when you don´t have a known
428 type.
429 void *talloc_memdup(const void *ctx, const void *p, size_t size);
431 The talloc_memdup() function is equivalent to:
432 ptr = talloc_size(ctx, size);
434 if (ptr) memcpy(ptr, p, size);
435 char *talloc_strdup(const void *ctx, const char *p);
437 The talloc_strdup() function is equivalent to:
438 ptr = talloc_size(ctx, strlen(p)+1);
440 if (ptr) memcpy(ptr, p, strlen(p)+1);
441 This function sets the name of the new pointer to the passed string.
443 This is equivalent to:
444 talloc_set_name_const(ptr, ptr)
446 char *talloc_strndup(const void *t, const char *p, size_t n);
448 The talloc_strndup() function is the talloc equivalent of the C library
449 function strndup(3).
450 This function sets the name of the new pointer to the passed string.
452 This is equivalent to:
453 talloc_set_name_const(ptr, ptr)
455 char *talloc_append_string(const void *t, char *orig, const char *append);
457 The talloc_append_string() function appends the given formatted string
458 to the given string.
459 This function sets the name of the new pointer to the new string. This
461 is equivalent to:
462 talloc_set_name_const(ptr, ptr)
464 char *talloc_vasprintf(const void *t, const char *fmt, va_list ap);
466 The talloc_vasprintf() function is the talloc equivalent of the C
467 library function vasprintf(3).
468 This function sets the name of the new pointer to the new string. This
470 is equivalent to:
471 talloc_set_name_const(ptr, ptr)
473 char *talloc_asprintf(const void *t, const char *fmt, ...);
475 The talloc_asprintf() function is the talloc equivalent of the C
476 library function asprintf(3).
477 This function sets the name of the new pointer to the passed string.
479 This is equivalent to:
480 talloc_set_name_const(ptr, ptr)
482 char *talloc_asprintf_append(char *s, const char *fmt, ...);
484 The talloc_asprintf_append() function appends the given formatted
485 string to the given string.
486 This function sets the name of the new pointer to the new string. This
488 is equivalent to:
489 talloc_set_name_const(ptr, ptr)
491 (type *)talloc_array(const void *ctx, type, uint_t count);
493 The talloc_array() macro is equivalent to:
494 (type *)talloc_size(ctx, sizeof(type) * count);
496 except that it provides integer overflow protection for the multiply,
498 returning NULL if the multiply overflows.
499 void *talloc_array_size(const void *ctx, size_t size, uint_t count);
501 The talloc_array_size() function is useful when the type is not known.
502 It operates in the same way as talloc_array(), but takes a size instead
503 of a type.
504 (typeof(ptr)) talloc_array_ptrtype(const void *ctx, ptr, uint_t count);
506 The talloc_ptrtype() macro should be used when you have a pointer to an
507 array and want to allocate memory of an array to point at with this
508 pointer. When compiling with gcc >= 3 it is typesafe. Note this is a
509 wrapper of talloc_array_size() and talloc_get_name() will return the
510 current location in the source file. and not the type.
511 void *talloc_realloc_fn(const void *ctx, void *ptr, size_t size)
513 This is a non-macro version of talloc_realloc(), which is useful as
514 libraries sometimes want a realloc function pointer. A realloc(3)
515 implementation encapsulates the functionality of malloc(3), free(3) and
516 realloc(3) in one call, which is why it is useful to be able to pass
517 around a single function pointer.
518 void *talloc_autofree_context(void);
520 This is a handy utility function that returns a talloc context which
521 will be automatically freed on program exit. This can be used to reduce
522 the noise in memory leak reports.
523 void *talloc_check_name(const void *ptr, const char *name);
525 This function checks if a pointer has the specified name. If it does
526 then the pointer is returned. It it doesn´t then NULL is returned.
527 (type *)talloc_get_type(const void *ptr, type);
529 This macro allows you to do type checking on talloc pointers. It is
530 particularly useful for void* private pointers. It is equivalent to
531 this:
532 (type *)talloc_check_name(ptr, #type)
534 talloc_set_type(const void *ptr, type);
536 This macro allows you to force the name of a pointer to be a particular
537 type. This can be used in conjunction with talloc_get_type() to do type
538 checking on void* pointers.
539 It is equivalent to this:
541 talloc_set_name_const(ptr, #type)
543 talloc_set_log_fn(void (*log_fn)(const char *message));
545 This function sets a logging function that talloc will use for warnings
546 and errors. By default talloc will not print any warnings or errors.
547 talloc_set_log_stderr(void);
549 This sets the talloc log function to write log messages to stderr
550
552 All the additional features of talloc(3) over malloc(3) do come at a
553 price. We have a simple performance test in Samba4 that measures
554 talloc() versus malloc() performance, and it seems that talloc() is
555 about 10% slower than malloc() on my x86 Debian Linux box. For Samba,
556 the great reduction in code complexity that we get by using talloc
557 makes this worthwhile, especially as the total overhead of
558 talloc/malloc in Samba is already quite small.
559
561 malloc(3), strndup(3), vasprintf(3), asprintf(3),
562 http://talloc.samba.org/
563
565 Copyright (C) Andrew Tridgell 2004
566 This program is free software; you can redistribute it and/or modify it
568 under the terms of the GNU General Public License as published by the
569 Free Software Foundation; either version 3 of the License, or (at your
570 option) any later version.
571 This program is distributed in the hope that it will be useful, but
573 WITHOUT ANY WARRANTY; without even the implied warranty of
574 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
575 General Public License for more details.
576 You should have received a copy of the GNU General Public License along
578 with this program; if not, see http://www.gnu.org/licenses/.
579[FIXME: source] 12/15/2009 TALLOC(3)