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1 /*
2 A version of malloc/free/realloc written by Doug Lea and released to the
3 public domain. Send questions/comments/complaints/performance data
4 to dl@cs.oswego.edu
6 * VERSION 2.6.6 Sun Mar 5 19:10:03 2000 Doug Lea (dl at gee)
8 Note: There may be an updated version of this malloc obtainable at
9 ftp://g.oswego.edu/pub/misc/malloc.c
10 Check before installing!
12 * Why use this malloc?
14 This is not the fastest, most space-conserving, most portable, or
15 most tunable malloc ever written. However it is among the fastest
16 while also being among the most space-conserving, portable and tunable.
17 Consistent balance across these factors results in a good general-purpose
18 allocator. For a high-level description, see
19 http://g.oswego.edu/dl/html/malloc.html
21 * Synopsis of public routines
23 (Much fuller descriptions are contained in the program documentation below.)
25 malloc(size_t n);
26 Return a pointer to a newly allocated chunk of at least n bytes, or null
27 if no space is available.
28 free(Void_t* p);
29 Release the chunk of memory pointed to by p, or no effect if p is null.
30 realloc(Void_t* p, size_t n);
31 Return a pointer to a chunk of size n that contains the same data
32 as does chunk p up to the minimum of (n, p's size) bytes, or null
33 if no space is available. The returned pointer may or may not be
34 the same as p. If p is null, equivalent to malloc. Unless the
35 #define REALLOC_ZERO_BYTES_FREES below is set, realloc with a
36 size argument of zero (re)allocates a minimum-sized chunk.
37 memalign(size_t alignment, size_t n);
38 Return a pointer to a newly allocated chunk of n bytes, aligned
39 in accord with the alignment argument, which must be a power of
40 two.
41 valloc(size_t n);
42 Equivalent to memalign(pagesize, n), where pagesize is the page
43 size of the system (or as near to this as can be figured out from
44 all the includes/defines below.)
45 pvalloc(size_t n);
46 Equivalent to valloc(minimum-page-that-holds(n)), that is,
47 round up n to nearest pagesize.
48 calloc(size_t unit, size_t quantity);
49 Returns a pointer to quantity * unit bytes, with all locations
50 set to zero.
51 cfree(Void_t* p);
52 Equivalent to free(p).
53 malloc_trim(size_t pad);
54 Release all but pad bytes of freed top-most memory back
55 to the system. Return 1 if successful, else 0.
56 malloc_usable_size(Void_t* p);
57 Report the number usable allocated bytes associated with allocated
58 chunk p. This may or may not report more bytes than were requested,
59 due to alignment and minimum size constraints.
60 malloc_stats();
61 Prints brief summary statistics on stderr.
62 mallinfo()
63 Returns (by copy) a struct containing various summary statistics.
64 mallopt(int parameter_number, int parameter_value)
65 Changes one of the tunable parameters described below. Returns
66 1 if successful in changing the parameter, else 0.
68 * Vital statistics:
70 Alignment: 8-byte
71 8 byte alignment is currently hardwired into the design. This
72 seems to suffice for all current machines and C compilers.
74 Assumed pointer representation: 4 or 8 bytes
75 Code for 8-byte pointers is untested by me but has worked
76 reliably by Wolfram Gloger, who contributed most of the
77 changes supporting this.
79 Assumed size_t representation: 4 or 8 bytes
80 Note that size_t is allowed to be 4 bytes even if pointers are 8.
82 Minimum overhead per allocated chunk: 4 or 8 bytes
83 Each malloced chunk has a hidden overhead of 4 bytes holding size
84 and status information.
86 Minimum allocated size: 4-byte ptrs: 16 bytes (including 4 overhead)
87 8-byte ptrs: 24/32 bytes (including, 4/8 overhead)
89 When a chunk is freed, 12 (for 4byte ptrs) or 20 (for 8 byte
90 ptrs but 4 byte size) or 24 (for 8/8) additional bytes are
91 needed; 4 (8) for a trailing size field
92 and 8 (16) bytes for free list pointers. Thus, the minimum
93 allocatable size is 16/24/32 bytes.
95 Even a request for zero bytes (i.e., malloc(0)) returns a
96 pointer to something of the minimum allocatable size.
98 Maximum allocated size: 4-byte size_t: 2^31 - 8 bytes
99 8-byte size_t: 2^63 - 16 bytes
101 It is assumed that (possibly signed) size_t bit values suffice to
102 represent chunk sizes. `Possibly signed' is due to the fact
103 that `size_t' may be defined on a system as either a signed or
104 an unsigned type. To be conservative, values that would appear
105 as negative numbers are avoided.
106 Requests for sizes with a negative sign bit when the request
107 size is treaded as a long will return null.
109 Maximum overhead wastage per allocated chunk: normally 15 bytes
111 Alignnment demands, plus the minimum allocatable size restriction
112 make the normal worst-case wastage 15 bytes (i.e., up to 15
113 more bytes will be allocated than were requested in malloc), with
114 two exceptions:
115 1. Because requests for zero bytes allocate non-zero space,
116 the worst case wastage for a request of zero bytes is 24 bytes.
117 2. For requests >= mmap_threshold that are serviced via
118 mmap(), the worst case wastage is 8 bytes plus the remainder
119 from a system page (the minimal mmap unit); typically 4096 bytes.
121 * Limitations
123 Here are some features that are NOT currently supported
125 * No user-definable hooks for callbacks and the like.
126 * No automated mechanism for fully checking that all accesses
127 to malloced memory stay within their bounds.
128 * No support for compaction.
130 * Synopsis of compile-time options:
132 People have reported using previous versions of this malloc on all
133 versions of Unix, sometimes by tweaking some of the defines
134 below. It has been tested most extensively on Solaris and
135 Linux. It is also reported to work on WIN32 platforms.
136 People have also reported adapting this malloc for use in
137 stand-alone embedded systems.
139 The implementation is in straight, hand-tuned ANSI C. Among other
140 consequences, it uses a lot of macros. Because of this, to be at
141 all usable, this code should be compiled using an optimizing compiler
142 (for example gcc -O2) that can simplify expressions and control
143 paths.
145 __STD_C (default: derived from C compiler defines)
146 Nonzero if using ANSI-standard C compiler, a C++ compiler, or
147 a C compiler sufficiently close to ANSI to get away with it.
148 DEBUG (default: NOT defined)
149 Define to enable debugging. Adds fairly extensive assertion-based
150 checking to help track down memory errors, but noticeably slows down
151 execution.
152 REALLOC_ZERO_BYTES_FREES (default: NOT defined)
153 Define this if you think that realloc(p, 0) should be equivalent
154 to free(p). Otherwise, since malloc returns a unique pointer for
155 malloc(0), so does realloc(p, 0).
156 HAVE_MEMCPY (default: defined)
157 Define if you are not otherwise using ANSI STD C, but still
158 have memcpy and memset in your C library and want to use them.
159 Otherwise, simple internal versions are supplied.
160 USE_MEMCPY (default: 1 if HAVE_MEMCPY is defined, 0 otherwise)
161 Define as 1 if you want the C library versions of memset and
162 memcpy called in realloc and calloc (otherwise macro versions are used).
163 At least on some platforms, the simple macro versions usually
164 outperform libc versions.
165 HAVE_MMAP (default: defined as 1)
166 Define to non-zero to optionally make malloc() use mmap() to
167 allocate very large blocks.
168 HAVE_MREMAP (default: defined as 0 unless Linux libc set)
169 Define to non-zero to optionally make realloc() use mremap() to
170 reallocate very large blocks.
171 malloc_getpagesize (default: derived from system #includes)
172 Either a constant or routine call returning the system page size.
173 HAVE_USR_INCLUDE_MALLOC_H (default: NOT defined)
174 Optionally define if you are on a system with a /usr/include/malloc.h
175 that declares struct mallinfo. It is not at all necessary to
176 define this even if you do, but will ensure consistency.
177 INTERNAL_SIZE_T (default: size_t)
178 Define to a 32-bit type (probably `unsigned int') if you are on a
179 64-bit machine, yet do not want or need to allow malloc requests of
180 greater than 2^31 to be handled. This saves space, especially for
181 very small chunks.
182 INTERNAL_LINUX_C_LIB (default: NOT defined)
183 Defined only when compiled as part of Linux libc.
184 Also note that there is some odd internal name-mangling via defines
185 (for example, internally, `malloc' is named `mALLOc') needed
186 when compiling in this case. These look funny but don't otherwise
187 affect anything.
188 WIN32 (default: undefined)
189 Define this on MS win (95, nt) platforms to compile in sbrk emulation.
190 LACKS_UNISTD_H (default: undefined if not WIN32)
191 Define this if your system does not have a <unistd.h>.
192 LACKS_SYS_PARAM_H (default: undefined if not WIN32)
193 Define this if your system does not have a <sys/param.h>.
194 MORECORE (default: sbrk)
195 The name of the routine to call to obtain more memory from the system.
196 MORECORE_FAILURE (default: -1)
197 The value returned upon failure of MORECORE.
198 MORECORE_CLEARS (default 1)
199 True (1) if the routine mapped to MORECORE zeroes out memory (which
200 holds for sbrk).
201 DEFAULT_TRIM_THRESHOLD
202 DEFAULT_TOP_PAD
203 DEFAULT_MMAP_THRESHOLD
204 DEFAULT_MMAP_MAX
205 Default values of tunable parameters (described in detail below)
206 controlling interaction with host system routines (sbrk, mmap, etc).
207 These values may also be changed dynamically via mallopt(). The
208 preset defaults are those that give best performance for typical
209 programs/systems.
210 USE_DL_PREFIX (default: undefined)
211 Prefix all public routines with the string 'dl'. Useful to
212 quickly avoid procedure declaration conflicts and linker symbol
213 conflicts with existing memory allocation routines.
216 */
218 \f
221 /* Preliminaries */
223 #ifndef __STD_C
224 #ifdef __STDC__
225 #define __STD_C 1
226 #else
227 #if __cplusplus
228 #define __STD_C 1
229 #else
230 #define __STD_C 0
235 #ifndef Void_t
236 #if (__STD_C || defined(WIN32))
237 #define Void_t void
238 #else
239 #define Void_t char
240 #endif
243 #if __STD_C
245 #else
246 #include <sys/types.h>
249 #ifdef __cplusplus
251 #endif
255 #endif
258 /*
259 Compile-time options
260 */
263 /*
264 Debugging:
266 Because freed chunks may be overwritten with link fields, this
267 malloc will often die when freed memory is overwritten by user
268 programs. This can be very effective (albeit in an annoying way)
269 in helping track down dangling pointers.
271 If you compile with -DDEBUG, a number of assertion checks are
272 enabled that will catch more memory errors. You probably won't be
273 able to make much sense of the actual assertion errors, but they
274 should help you locate incorrectly overwritten memory. The
275 checking is fairly extensive, and will slow down execution
276 noticeably. Calling malloc_stats or mallinfo with DEBUG set will
277 attempt to check every non-mmapped allocated and free chunk in the
278 course of computing the summmaries. (By nature, mmapped regions
279 cannot be checked very much automatically.)
281 Setting DEBUG may also be helpful if you are trying to modify
282 this code. The assertions in the check routines spell out in more
283 detail the assumptions and invariants underlying the algorithms.
285 */
287 #ifdef DEBUG
288 /* #include <assert.h> */
289 #define assert(x) ((void)0)
290 #else
291 #define assert(x) ((void)0)
292 #endif
295 /*
296 INTERNAL_SIZE_T is the word-size used for internal bookkeeping
297 of chunk sizes. On a 64-bit machine, you can reduce malloc
298 overhead by defining INTERNAL_SIZE_T to be a 32 bit `unsigned int'
299 at the expense of not being able to handle requests greater than
300 2^31. This limitation is hardly ever a concern; you are encouraged
301 to set this. However, the default version is the same as size_t.
302 */
304 #ifndef INTERNAL_SIZE_T
305 #define INTERNAL_SIZE_T size_t
306 #endif
308 /*
309 REALLOC_ZERO_BYTES_FREES should be set if a call to
310 realloc with zero bytes should be the same as a call to free.
311 Some people think it should. Otherwise, since this malloc
312 returns a unique pointer for malloc(0), so does realloc(p, 0).
313 */
316 /* #define REALLOC_ZERO_BYTES_FREES */
319 /*
320 WIN32 causes an emulation of sbrk to be compiled in
321 mmap-based options are not currently supported in WIN32.
322 */
324 /* #define WIN32 */
325 #ifdef WIN32
326 #define MORECORE wsbrk
327 #define HAVE_MMAP 0
329 #define LACKS_UNISTD_H
330 #define LACKS_SYS_PARAM_H
332 /*
333 Include 'windows.h' to get the necessary declarations for the
334 Microsoft Visual C++ data structures and routines used in the 'sbrk'
335 emulation.
337 Define WIN32_LEAN_AND_MEAN so that only the essential Microsoft
338 Visual C++ header files are included.
339 */
340 #define WIN32_LEAN_AND_MEAN
341 #include <windows.h>
342 #endif
345 /*
346 HAVE_MEMCPY should be defined if you are not otherwise using
347 ANSI STD C, but still have memcpy and memset in your C library
348 and want to use them in calloc and realloc. Otherwise simple
349 macro versions are defined here.
351 USE_MEMCPY should be defined as 1 if you actually want to
352 have memset and memcpy called. People report that the macro
353 versions are often enough faster than libc versions on many
354 systems that it is better to use them.
356 */
358 #define HAVE_MEMCPY
360 #ifndef USE_MEMCPY
361 #ifdef HAVE_MEMCPY
362 #define USE_MEMCPY 1
363 #else
364 #define USE_MEMCPY 0
365 #endif
366 #endif
368 #if (__STD_C || defined(HAVE_MEMCPY))
370 #if __STD_C
373 #else
374 #ifdef WIN32
375 /* On Win32 platforms, 'memset()' and 'memcpy()' are already declared in */
376 /* 'windows.h' */
377 #else
380 #endif
381 #endif
382 #endif
384 #if USE_MEMCPY
386 /* The following macros are only invoked with (2n+1)-multiples of
387 INTERNAL_SIZE_T units, with a positive integer n. This is exploited
388 for fast inline execution when n is small. */
390 #define MALLOC_ZERO(charp, nbytes) \
391 do { \
392 INTERNAL_SIZE_T mzsz = (nbytes); \
393 if(mzsz <= 9*sizeof(mzsz)) { \
394 INTERNAL_SIZE_T* mz = (INTERNAL_SIZE_T*) (charp); \
395 if(mzsz >= 5*sizeof(mzsz)) { *mz++ = 0; \
396 *mz++ = 0; \
397 if(mzsz >= 7*sizeof(mzsz)) { *mz++ = 0; \
398 *mz++ = 0; \
399 if(mzsz >= 9*sizeof(mzsz)) { *mz++ = 0; \
400 *mz++ = 0; }}} \
401 *mz++ = 0; \
402 *mz++ = 0; \
403 *mz = 0; \
404 } else memset((charp), 0, mzsz); \
405 } while(0)
407 #define MALLOC_COPY(dest,src,nbytes) \
408 do { \
409 INTERNAL_SIZE_T mcsz = (nbytes); \
410 if(mcsz <= 9*sizeof(mcsz)) { \
411 INTERNAL_SIZE_T* mcsrc = (INTERNAL_SIZE_T*) (src); \
412 INTERNAL_SIZE_T* mcdst = (INTERNAL_SIZE_T*) (dest); \
413 if(mcsz >= 5*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \
414 *mcdst++ = *mcsrc++; \
415 if(mcsz >= 7*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \
416 *mcdst++ = *mcsrc++; \
417 if(mcsz >= 9*sizeof(mcsz)) { *mcdst++ = *mcsrc++; \
418 *mcdst++ = *mcsrc++; }}} \
419 *mcdst++ = *mcsrc++; \
420 *mcdst++ = *mcsrc++; \
421 *mcdst = *mcsrc ; \
422 } else memcpy(dest, src, mcsz); \
423 } while(0)
427 /* Use Duff's device for good zeroing/copying performance. */
429 #define MALLOC_ZERO(charp, nbytes) \
430 do { \
431 INTERNAL_SIZE_T* mzp = (INTERNAL_SIZE_T*)(charp); \
432 long mctmp = (nbytes)/sizeof(INTERNAL_SIZE_T), mcn; \
433 if (mctmp < 8) mcn = 0; else { mcn = (mctmp-1)/8; mctmp %= 8; } \
434 switch (mctmp) { \
435 case 0: for(;;) { *mzp++ = 0; \
436 case 7: *mzp++ = 0; \
437 case 6: *mzp++ = 0; \
438 case 5: *mzp++ = 0; \
439 case 4: *mzp++ = 0; \
440 case 3: *mzp++ = 0; \
441 case 2: *mzp++ = 0; \
442 case 1: *mzp++ = 0; if(mcn <= 0) break; mcn--; } \
443 } \
444 } while(0)
446 #define MALLOC_COPY(dest,src,nbytes) \
447 do { \
448 INTERNAL_SIZE_T* mcsrc = (INTERNAL_SIZE_T*) src; \
449 INTERNAL_SIZE_T* mcdst = (INTERNAL_SIZE_T*) dest; \
450 long mctmp = (nbytes)/sizeof(INTERNAL_SIZE_T), mcn; \
451 if (mctmp < 8) mcn = 0; else { mcn = (mctmp-1)/8; mctmp %= 8; } \
452 switch (mctmp) { \
453 case 0: for(;;) { *mcdst++ = *mcsrc++; \
454 case 7: *mcdst++ = *mcsrc++; \
455 case 6: *mcdst++ = *mcsrc++; \
456 case 5: *mcdst++ = *mcsrc++; \
457 case 4: *mcdst++ = *mcsrc++; \
458 case 3: *mcdst++ = *mcsrc++; \
459 case 2: *mcdst++ = *mcsrc++; \
460 case 1: *mcdst++ = *mcsrc++; if(mcn <= 0) break; mcn--; } \
461 } \
462 } while(0)
464 #endif
467 /*
468 Define HAVE_MMAP to optionally make malloc() use mmap() to
469 allocate very large blocks. These will be returned to the
470 operating system immediately after a free().
471 */
473 /***
474 #ifndef HAVE_MMAP
475 #define HAVE_MMAP 1
476 #endif
477 ***/
480 /*
481 Define HAVE_MREMAP to make realloc() use mremap() to re-allocate
482 large blocks. This is currently only possible on Linux with
483 kernel versions newer than 1.3.77.
484 */
486 /***
487 #ifndef HAVE_MREMAP
488 #ifdef INTERNAL_LINUX_C_LIB
489 #define HAVE_MREMAP 1
490 #else
491 #define HAVE_MREMAP 0
492 #endif
493 #endif
494 ***/
497 #if HAVE_MMAP
499 #include <unistd.h>
500 #include <fcntl.h>
501 #include <sys/mman.h>
503 #if !defined(MAP_ANONYMOUS) && defined(MAP_ANON)
504 #define MAP_ANONYMOUS MAP_ANON
505 #endif
509 /*
510 Access to system page size. To the extent possible, this malloc
511 manages memory from the system in page-size units.
513 The following mechanics for getpagesize were adapted from
514 bsd/gnu getpagesize.h
515 */
518 #define malloc_getpagesize 4096
520 #ifndef LACKS_UNISTD_H
521 # include <unistd.h>
522 #endif
524 #ifndef malloc_getpagesize
526 # ifndef _SC_PAGE_SIZE
527 # define _SC_PAGE_SIZE _SC_PAGESIZE
528 # endif
529 # endif
530 # ifdef _SC_PAGE_SIZE
531 # define malloc_getpagesize sysconf(_SC_PAGE_SIZE)
532 # else
533 # if defined(BSD) || defined(DGUX) || defined(HAVE_GETPAGESIZE)
535 # define malloc_getpagesize getpagesize()
536 # else
537 # ifdef WIN32
539 # else
540 # ifndef LACKS_SYS_PARAM_H
541 # include <sys/param.h>
542 # endif
543 # ifdef EXEC_PAGESIZE
544 # define malloc_getpagesize EXEC_PAGESIZE
545 # else
546 # ifdef NBPG
547 # ifndef CLSIZE
548 # define malloc_getpagesize NBPG
549 # else
550 # define malloc_getpagesize (NBPG * CLSIZE)
551 # endif
552 # else
553 # ifdef NBPC
554 # define malloc_getpagesize NBPC
555 # else
556 # ifdef PAGESIZE
557 # define malloc_getpagesize PAGESIZE
558 # else
560 # endif
561 # endif
562 # endif
563 # endif
564 # endif
565 # endif
566 # endif
567 #endif
570 /*
572 This version of malloc supports the standard SVID/XPG mallinfo
573 routine that returns a struct containing the same kind of
574 information you can get from malloc_stats. It should work on
575 any SVID/XPG compliant system that has a /usr/include/malloc.h
576 defining struct mallinfo. (If you'd like to install such a thing
577 yourself, cut out the preliminary declarations as described above
578 and below and save them in a malloc.h file. But there's no
579 compelling reason to bother to do this.)
581 The main declaration needed is the mallinfo struct that is returned
582 (by-copy) by mallinfo(). The SVID/XPG malloinfo struct contains a
583 bunch of fields, most of which are not even meaningful in this
584 version of malloc. Some of these fields are are instead filled by
585 mallinfo() with other numbers that might possibly be of interest.
587 HAVE_USR_INCLUDE_MALLOC_H should be set if you have a
588 /usr/include/malloc.h file that includes a declaration of struct
589 mallinfo. If so, it is included; else an SVID2/XPG2 compliant
590 version is declared below. These must be precisely the same for
591 mallinfo() to work.
593 */
595 /* #define HAVE_USR_INCLUDE_MALLOC_H */
597 #if HAVE_USR_INCLUDE_MALLOC_H
599 #else
601 /* SVID2/XPG mallinfo structure */
614 };
616 /* SVID2/XPG mallopt options */
623 #endif
625 /* mallopt options that actually do something */
627 #define M_TRIM_THRESHOLD -1
628 #define M_TOP_PAD -2
629 #define M_MMAP_THRESHOLD -3
630 #define M_MMAP_MAX -4
633 #ifndef DEFAULT_TRIM_THRESHOLD
634 #define DEFAULT_TRIM_THRESHOLD (128 * 1024)
635 #endif
637 /*
638 M_TRIM_THRESHOLD is the maximum amount of unused top-most memory
639 to keep before releasing via malloc_trim in free().
641 Automatic trimming is mainly useful in long-lived programs.
642 Because trimming via sbrk can be slow on some systems, and can
643 sometimes be wasteful (in cases where programs immediately
644 afterward allocate more large chunks) the value should be high
645 enough so that your overall system performance would improve by
646 releasing.
648 The trim threshold and the mmap control parameters (see below)
649 can be traded off with one another. Trimming and mmapping are
650 two different ways of releasing unused memory back to the
651 system. Between these two, it is often possible to keep
652 system-level demands of a long-lived program down to a bare
653 minimum. For example, in one test suite of sessions measuring
654 the XF86 X server on Linux, using a trim threshold of 128K and a
655 mmap threshold of 192K led to near-minimal long term resource
656 consumption.
658 If you are using this malloc in a long-lived program, it should
659 pay to experiment with these values. As a rough guide, you
660 might set to a value close to the average size of a process
661 (program) running on your system. Releasing this much memory
662 would allow such a process to run in memory. Generally, it's
663 worth it to tune for trimming rather tham memory mapping when a
664 program undergoes phases where several large chunks are
665 allocated and released in ways that can reuse each other's
666 storage, perhaps mixed with phases where there are no such
667 chunks at all. And in well-behaved long-lived programs,
668 controlling release of large blocks via trimming versus mapping
669 is usually faster.
671 However, in most programs, these parameters serve mainly as
672 protection against the system-level effects of carrying around
673 massive amounts of unneeded memory. Since frequent calls to
674 sbrk, mmap, and munmap otherwise degrade performance, the default
675 parameters are set to relatively high values that serve only as
676 safeguards.
678 The default trim value is high enough to cause trimming only in
679 fairly extreme (by current memory consumption standards) cases.
680 It must be greater than page size to have any useful effect. To
681 disable trimming completely, you can set to (unsigned long)(-1);
684 */
687 #ifndef DEFAULT_TOP_PAD
688 #define DEFAULT_TOP_PAD (0)
689 #endif
691 /*
692 M_TOP_PAD is the amount of extra `padding' space to allocate or
693 retain whenever sbrk is called. It is used in two ways internally:
695 * When sbrk is called to extend the top of the arena to satisfy
696 a new malloc request, this much padding is added to the sbrk
697 request.
699 * When malloc_trim is called automatically from free(),
700 it is used as the `pad' argument.
702 In both cases, the actual amount of padding is rounded
703 so that the end of the arena is always a system page boundary.
705 The main reason for using padding is to avoid calling sbrk so
706 often. Having even a small pad greatly reduces the likelihood
707 that nearly every malloc request during program start-up (or
708 after trimming) will invoke sbrk, which needlessly wastes
709 time.
711 Automatic rounding-up to page-size units is normally sufficient
712 to avoid measurable overhead, so the default is 0. However, in
713 systems where sbrk is relatively slow, it can pay to increase
714 this value, at the expense of carrying around more memory than
715 the program needs.
717 */
720 #ifndef DEFAULT_MMAP_THRESHOLD
721 #define DEFAULT_MMAP_THRESHOLD (128 * 1024)
722 #endif
724 /*
726 M_MMAP_THRESHOLD is the request size threshold for using mmap()
727 to service a request. Requests of at least this size that cannot
728 be allocated using already-existing space will be serviced via mmap.
729 (If enough normal freed space already exists it is used instead.)
731 Using mmap segregates relatively large chunks of memory so that
732 they can be individually obtained and released from the host
733 system. A request serviced through mmap is never reused by any
734 other request (at least not directly; the system may just so
735 happen to remap successive requests to the same locations).
737 Segregating space in this way has the benefit that mmapped space
738 can ALWAYS be individually released back to the system, which
739 helps keep the system level memory demands of a long-lived
740 program low. Mapped memory can never become `locked' between
741 other chunks, as can happen with normally allocated chunks, which
742 menas that even trimming via malloc_trim would not release them.
744 However, it has the disadvantages that:
746 1. The space cannot be reclaimed, consolidated, and then
747 used to service later requests, as happens with normal chunks.
748 2. It can lead to more wastage because of mmap page alignment
749 requirements
750 3. It causes malloc performance to be more dependent on host
751 system memory management support routines which may vary in
752 implementation quality and may impose arbitrary
753 limitations. Generally, servicing a request via normal
754 malloc steps is faster than going through a system's mmap.
756 All together, these considerations should lead you to use mmap
757 only for relatively large requests.
760 */
763 #ifndef DEFAULT_MMAP_MAX
764 #if HAVE_MMAP
765 #define DEFAULT_MMAP_MAX (64)
766 #else
767 #define DEFAULT_MMAP_MAX (0)
768 #endif
769 #endif
771 /*
772 M_MMAP_MAX is the maximum number of requests to simultaneously
773 service using mmap. This parameter exists because:
775 1. Some systems have a limited number of internal tables for
776 use by mmap.
777 2. In most systems, overreliance on mmap can degrade overall
778 performance.
779 3. If a program allocates many large regions, it is probably
780 better off using normal sbrk-based allocation routines that
781 can reclaim and reallocate normal heap memory. Using a
782 small value allows transition into this mode after the
783 first few allocations.
785 Setting to 0 disables all use of mmap. If HAVE_MMAP is not set,
786 the default value is 0, and attempts to set it to non-zero values
787 in mallopt will fail.
788 */
791 /*
792 USE_DL_PREFIX will prefix all public routines with the string 'dl'.
793 Useful to quickly avoid procedure declaration conflicts and linker
794 symbol conflicts with existing memory allocation routines.
796 */
798 /* #define USE_DL_PREFIX */
801 /*
803 Special defines for linux libc
805 Except when compiled using these special defines for Linux libc
806 using weak aliases, this malloc is NOT designed to work in
807 multithreaded applications. No semaphores or other concurrency
808 control are provided to ensure that multiple malloc or free calls
809 don't run at the same time, which could be disasterous. A single
810 semaphore could be used across malloc, realloc, and free (which is
811 essentially the effect of the linux weak alias approach). It would
812 be hard to obtain finer granularity.
814 */
817 #ifdef INTERNAL_LINUX_C_LIB
819 #if __STD_C
824 #else
829 #endif
831 #define MORECORE (*__morecore)
832 #define MORECORE_FAILURE 0
833 #define MORECORE_CLEARS 1
837 #if __STD_C
839 #else
841 #endif
843 #ifndef MORECORE
844 #define MORECORE sbrk
845 #endif
847 #ifndef MORECORE_FAILURE
848 #define MORECORE_FAILURE -1
849 #endif
851 #ifndef MORECORE_CLEARS
852 #define MORECORE_CLEARS 1
853 #endif
857 #if defined(INTERNAL_LINUX_C_LIB) && defined(__ELF__)
859 #define cALLOc __libc_calloc
860 #define fREe __libc_free
861 #define mALLOc __libc_malloc
862 #define mEMALIGn __libc_memalign
863 #define rEALLOc __libc_realloc
864 #define vALLOc __libc_valloc
865 #define pvALLOc __libc_pvalloc
866 #define mALLINFo __libc_mallinfo
867 #define mALLOPt __libc_mallopt
869 #pragma weak calloc = __libc_calloc
870 #pragma weak free = __libc_free
871 #pragma weak cfree = __libc_free
872 #pragma weak malloc = __libc_malloc
873 #pragma weak memalign = __libc_memalign
874 #pragma weak realloc = __libc_realloc
875 #pragma weak valloc = __libc_valloc
876 #pragma weak pvalloc = __libc_pvalloc
877 #pragma weak mallinfo = __libc_mallinfo
878 #pragma weak mallopt = __libc_mallopt
880 #else
882 #ifdef USE_DL_PREFIX
883 #define cALLOc dlcalloc
884 #define fREe dlfree
885 #define mALLOc dlmalloc
886 #define mEMALIGn dlmemalign
887 #define rEALLOc dlrealloc
888 #define vALLOc dlvalloc
889 #define pvALLOc dlpvalloc
890 #define mALLINFo dlmallinfo
891 #define mALLOPt dlmallopt
893 #define cALLOc calloc
894 #define fREe free
895 #define mALLOc malloc
896 #define mEMALIGn memalign
897 #define rEALLOc realloc
898 #define vALLOc valloc
899 #define pvALLOc pvalloc
900 #define mALLINFo mallinfo
901 #define mALLOPt mallopt
904 #endif
906 /* Public routines */
908 #if __STD_C
923 #else
937 #endif
940 #ifdef __cplusplus
942 #endif