mtmalloc, mallocctl - MT hot memory allocator
cc -o a.out -lthread -lmtmalloc
void *malloc(size_t size);
void free(void *ptr);
void *memalign(size_t alignment, size_t size);
void *realloc(void *ptr, size_t size);
void *valloc(size_t size);
void mallocctl(int cmd, long value);
The malloc() and free() functions provide a simple general-purpose mem‐
ory allocation package that is suitable for use in high performance
multithreaded applications. The suggested use of this library is in
multithreaded applications; it can be used for single threaded appli‐
cations, but there is no advantage in doing so. This library cannot be
dynamically loaded with dlopen(3C) during runtime because there must be
only one manager of the process heap.
The malloc() function returns a pointer to a block of at least size
bytes suitably aligned for any use.
The argument to free() is a pointer to a block previously allocated by
malloc() or realloc(). After free() is performed this space is avail‐
able for further allocation. If ptr is a null pointer, no action
occurs. The free() function does not set errno.
Undefined results will occur if the space assigned by malloc() is over‐
run or if a random number is handed to free(). A freed pointer that is
passed to free() will send a SIGABRT signal to the calling process.
This behavior is controlled by mallocctl().
The memalign() function allocates size bytes on a specified alignment
boundary and returns a pointer to the allocated block. The value of the
returned address is guaranteed to be an even multiple of alignment.
Note that the value of alignment must be a power of two, and must be
greater than or equal to the size of a word.
The realloc() function changes the size of the block pointed to by ptr
to size bytes and returns a pointer to the (possibly moved) block. The
contents will be unchanged up to the lesser of the new and old sizes.
If the new size of the block requires movement of the block, the space
for the previous instantiation of the block is freed. If the new size
is larger, the contents of the newly allocated portion of the block are
unspecified. If ptr is NULL, realloc() behaves like malloc() for the
specified size. If size is 0 and ptr is not a null pointer, the space
pointed to is freed.
The valloc() function has the same effect as malloc(), except that the
allocated memory will be aligned to a multiple of the value returned by
After possible pointer coercion, each allocation routine returns a
pointer to a space that is suitably aligned for storage of any type of
The malloc(), realloc(), memalign(), and valloc() functions will fail
if there is not enough available memory.
The mallocctl() function controls the behavior of the malloc library.
The options fall into two general classes, debugging options and per‐
Allows double free of a pointer. Setting value to
1 means yes and 0 means no. The default behavior of
double free results in a core dump.
Writes misaligned data into the buffer after free().
When the buffer is reallocated, the contents are ver‐
ified to ensure that there was no access to the buf‐
fer after the free. If the buffer has been dirtied, a
SIGABRT signal is delivered to the process. Setting
value to 1 means yes and 0 means no. The default
behavior is to not write misaligned data. The pat‐
tern used is 0xdeadbeef. Use of this option results
in a performance penalty.
Writes misaligned data into the newly allocated buf‐
fer. This option is useful for detecting some
accesses before initialization. Setting value to 1
means yes and 0 means no. The default behavior is to
not write misaligned data to the newly allocated buf‐
fer. The pattern used is 0xbaddcafe. Use of this
option results in a performance penalty.
This option changes the size of allocated memory when
a pool has exhausted all available memory in the buf‐
fer. Increasing this value allocates more memory for
the application. A substantial performance gain can
occur because the library makes fewer calls to the
OS for more memory. Acceptable number values are
between 9 and 256. The default value is 9. This
value is multiplied by 8192.
If there is no available memory, malloc(), realloc(), memalign(), and
valloc() return a null pointer. When realloc() is called with size > 0
and returns NULL, the block pointed to by ptr is left intact. If size,
nelem, or elsize is 0, either a null pointer or a unique pointer that
can be passed to free() is returned.
If malloc() or realloc() returns unsuccessfully, errno will be set to
indicate the error.
The malloc() and realloc() functions will fail if:
The physical limits of the system are exceeded by size bytes
of memory which cannot be allocated.
There is not enough memory available to allocate size bytes
of memory; but the application could try again later.
Comparative features of the various allocation libraries can be found
in the umem_alloc(3MALLOC) manual page.
See attributes(5) for descriptions of the following attributes:
│ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│MT-Level │ Safe │
SEE ALSObrk(2), getrlimit(2), bsdmalloc(3MALLOC), dlopen(3C), malloc(3C), mal‐
loc(3MALLOC), mapmalloc(3MALLOC), signal.h(3HEAD), umem_alloc(3MALLOC),
Undefined results will occur if the size requested for a block of mem‐
ory exceeds the maximum size of a process's heap. This information may
be obtained using getrlimit().
Mar 21, 2005 MTMALLOC(3MALLOC)