path: root/common/dlmalloc.c
diff options
authorJuergen Beisert <>2009-12-10 13:09:02 +0100
committerJuergen Beisert <>2009-12-10 13:09:02 +0100
commit7fd641558b18aec7cc2fa44f12ccbb54e01fb504 (patch)
treeb23d7e091bf8e7a67f62fbaf065587d17ce6fd5e /common/dlmalloc.c
parente954ee06474efc0b975f0a52cdd7478990a6e938 (diff)
After moving all declarations to the C source, do the same with the doc
Done in preparation to provide this documentation for doxygen. Signed-off-by: Juergen Beisert <>
Diffstat (limited to 'common/dlmalloc.c')
1 files changed, 217 insertions, 0 deletions
diff --git a/common/dlmalloc.c b/common/dlmalloc.c
index 3db7c00..2ebb6e7 100644
--- a/common/dlmalloc.c
+++ b/common/dlmalloc.c
@@ -5,6 +5,223 @@
#include <stdio.h>
#include <module.h>
+ A version of malloc/free/realloc written by Doug Lea and released to the
+ public domain. Send questions/comments/complaints/performance data
+ to
+* VERSION 2.6.6 Sun Mar 5 19:10:03 2000 Doug Lea (dl at gee)
+ Note: There may be an updated version of this malloc obtainable at
+ Check before installing!
+* Why use this malloc?
+ This is not the fastest, most space-conserving, most portable, or
+ most tunable malloc ever written. However it is among the fastest
+ while also being among the most space-conserving, portable and tunable.
+ Consistent balance across these factors results in a good general-purpose
+ allocator. For a high-level description, see
+* Synopsis of public routines
+ (Much fuller descriptions are contained in the program documentation below.)
+ malloc(size_t n);
+ Return a pointer to a newly allocated chunk of at least n bytes, or null
+ if no space is available.
+ free(Void_t* p);
+ Release the chunk of memory pointed to by p, or no effect if p is null.
+ realloc(Void_t* p, size_t n);
+ Return a pointer to a chunk of size n that contains the same data
+ as does chunk p up to the minimum of (n, p's size) bytes, or null
+ if no space is available. The returned pointer may or may not be
+ the same as p. If p is null, equivalent to malloc. Unless the
+ #define REALLOC_ZERO_BYTES_FREES below is set, realloc with a
+ size argument of zero (re)allocates a minimum-sized chunk.
+ memalign(size_t alignment, size_t n);
+ Return a pointer to a newly allocated chunk of n bytes, aligned
+ in accord with the alignment argument, which must be a power of
+ two.
+ valloc(size_t n);
+ Equivalent to memalign(pagesize, n), where pagesize is the page
+ size of the system (or as near to this as can be figured out from
+ all the includes/defines below.)
+ pvalloc(size_t n);
+ Equivalent to valloc(minimum-page-that-holds(n)), that is,
+ round up n to nearest pagesize.
+ calloc(size_t unit, size_t quantity);
+ Returns a pointer to quantity * unit bytes, with all locations
+ set to zero.
+ cfree(Void_t* p);
+ Equivalent to free(p).
+ malloc_trim(size_t pad);
+ Release all but pad bytes of freed top-most memory back
+ to the system. Return 1 if successful, else 0.
+ malloc_usable_size(Void_t* p);
+ Report the number usable allocated bytes associated with allocated
+ chunk p. This may or may not report more bytes than were requested,
+ due to alignment and minimum size constraints.
+ malloc_stats();
+ Prints brief summary statistics on stderr.
+ mallinfo()
+ Returns (by copy) a struct containing various summary statistics.
+ mallopt(int parameter_number, int parameter_value)
+ Changes one of the tunable parameters described below. Returns
+ 1 if successful in changing the parameter, else 0.
+* Vital statistics:
+ Alignment: 8-byte
+ 8 byte alignment is currently hardwired into the design. This
+ seems to suffice for all current machines and C compilers.
+ Assumed pointer representation: 4 or 8 bytes
+ Code for 8-byte pointers is untested by me but has worked
+ reliably by Wolfram Gloger, who contributed most of the
+ changes supporting this.
+ Assumed size_t representation: 4 or 8 bytes
+ Note that size_t is allowed to be 4 bytes even if pointers are 8.
+ Minimum overhead per allocated chunk: 4 or 8 bytes
+ Each malloced chunk has a hidden overhead of 4 bytes holding size
+ and status information.
+ Minimum allocated size: 4-byte ptrs: 16 bytes (including 4 overhead)
+ 8-byte ptrs: 24/32 bytes (including, 4/8 overhead)
+ When a chunk is freed, 12 (for 4byte ptrs) or 20 (for 8 byte
+ ptrs but 4 byte size) or 24 (for 8/8) additional bytes are
+ needed; 4 (8) for a trailing size field
+ and 8 (16) bytes for free list pointers. Thus, the minimum
+ allocatable size is 16/24/32 bytes.
+ Even a request for zero bytes (i.e., malloc(0)) returns a
+ pointer to something of the minimum allocatable size.
+ Maximum allocated size: 4-byte size_t: 2^31 - 8 bytes
+ 8-byte size_t: 2^63 - 16 bytes
+ It is assumed that (possibly signed) size_t bit values suffice to
+ represent chunk sizes. `Possibly signed' is due to the fact
+ that `size_t' may be defined on a system as either a signed or
+ an unsigned type. To be conservative, values that would appear
+ as negative numbers are avoided.
+ Requests for sizes with a negative sign bit when the request
+ size is treaded as a long will return null.
+ Maximum overhead wastage per allocated chunk: normally 15 bytes
+ Alignnment demands, plus the minimum allocatable size restriction
+ make the normal worst-case wastage 15 bytes (i.e., up to 15
+ more bytes will be allocated than were requested in malloc), with
+ two exceptions:
+ 1. Because requests for zero bytes allocate non-zero space,
+ the worst case wastage for a request of zero bytes is 24 bytes.
+ 2. For requests >= mmap_threshold that are serviced via
+ mmap(), the worst case wastage is 8 bytes plus the remainder
+ from a system page (the minimal mmap unit); typically 4096 bytes.
+* Limitations
+ Here are some features that are NOT currently supported
+ * No user-definable hooks for callbacks and the like.
+ * No automated mechanism for fully checking that all accesses
+ to malloced memory stay within their bounds.
+ * No support for compaction.
+* Synopsis of compile-time options:
+ People have reported using previous versions of this malloc on all
+ versions of Unix, sometimes by tweaking some of the defines
+ below. It has been tested most extensively on Solaris and
+ Linux. It is also reported to work on WIN32 platforms.
+ People have also reported adapting this malloc for use in
+ stand-alone embedded systems.
+ The implementation is in straight, hand-tuned ANSI C. Among other
+ consequences, it uses a lot of macros. Because of this, to be at
+ all usable, this code should be compiled using an optimizing compiler
+ (for example gcc -O2) that can simplify expressions and control
+ paths.
+ __STD_C (default: derived from C compiler defines)
+ Nonzero if using ANSI-standard C compiler, a C++ compiler, or
+ a C compiler sufficiently close to ANSI to get away with it.
+ DEBUG (default: NOT defined)
+ Define to enable debugging. Adds fairly extensive assertion-based
+ checking to help track down memory errors, but noticeably slows down
+ execution.
+ REALLOC_ZERO_BYTES_FREES (default: NOT defined)
+ Define this if you think that realloc(p, 0) should be equivalent
+ to free(p). Otherwise, since malloc returns a unique pointer for
+ malloc(0), so does realloc(p, 0).
+ HAVE_MEMCPY (default: defined)
+ Define if you are not otherwise using ANSI STD C, but still
+ have memcpy and memset in your C library and want to use them.
+ Otherwise, simple internal versions are supplied.
+ USE_MEMCPY (default: 1 if HAVE_MEMCPY is defined, 0 otherwise)
+ Define as 1 if you want the C library versions of memset and
+ memcpy called in realloc and calloc (otherwise macro versions are used).
+ At least on some platforms, the simple macro versions usually
+ outperform libc versions.
+ HAVE_MMAP (default: defined as 1)
+ Define to non-zero to optionally make malloc() use mmap() to
+ allocate very large blocks.
+ HAVE_MREMAP (default: defined as 0 unless Linux libc set)
+ Define to non-zero to optionally make realloc() use mremap() to
+ reallocate very large blocks.
+ malloc_getpagesize (default: derived from system #includes)
+ Either a constant or routine call returning the system page size.
+ HAVE_USR_INCLUDE_MALLOC_H (default: NOT defined)
+ Optionally define if you are on a system with a /usr/include/malloc.h
+ that declares struct mallinfo. It is not at all necessary to
+ define this even if you do, but will ensure consistency.
+ INTERNAL_SIZE_T (default: size_t)
+ Define to a 32-bit type (probably `unsigned int') if you are on a
+ 64-bit machine, yet do not want or need to allow malloc requests of
+ greater than 2^31 to be handled. This saves space, especially for
+ very small chunks.
+ INTERNAL_LINUX_C_LIB (default: NOT defined)
+ Defined only when compiled as part of Linux libc.
+ Also note that there is some odd internal name-mangling via defines
+ (for example, internally, `malloc' is named `mALLOc') needed
+ when compiling in this case. These look funny but don't otherwise
+ affect anything.
+ WIN32 (default: undefined)
+ Define this on MS win (95, nt) platforms to compile in sbrk emulation.
+ LACKS_UNISTD_H (default: undefined if not WIN32)
+ Define this if your system does not have a <unistd.h>.
+ LACKS_SYS_PARAM_H (default: undefined if not WIN32)
+ Define this if your system does not have a <sys/param.h>.
+ MORECORE (default: sbrk)
+ The name of the routine to call to obtain more memory from the system.
+ MORECORE_FAILURE (default: -1)
+ The value returned upon failure of MORECORE.
+ MORECORE_CLEARS (default 1)
+ True (1) if the routine mapped to MORECORE zeroes out memory (which
+ holds for sbrk).
+ Default values of tunable parameters (described in detail below)
+ controlling interaction with host system routines (sbrk, mmap, etc).
+ These values may also be changed dynamically via mallopt(). The
+ preset defaults are those that give best performance for typical
+ programs/systems.
+ USE_DL_PREFIX (default: undefined)
+ Prefix all public routines with the string 'dl'. Useful to
+ quickly avoid procedure declaration conflicts and linker symbol
+ conflicts with existing memory allocation routines.
/* to be able to compile this file (is going to be removed) */
#define __STD_C 1