Tribblix: manual page: mtmalloc.3malloc

MTMALLOC(3MALLOC) Memory Allocation Library Functions MTMALLOC(3MALLOC)

NAME

mtmalloc, mallocctl - MT hot memory allocator

SYNOPSIS

#include <mtmalloc.h>
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);

DESCRIPTION

The malloc() and free() functions provide a simple general-purpose
memory 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 applications, 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
available 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
overrun 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 sysconf(_SC_PAGESIZE).

After possible pointer coercion, each allocation routine returns a
pointer to a space that is suitably aligned for storage of any type
of object.

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
performance options.

MTDOUBLEFREE
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.

MTDEBUGPATTERN
Writes misaligned data into the buffer after
free(). When the buffer is reallocated, the
contents are verified to ensure that there was no
access to the buffer 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 pattern used is 0xdeadbeef.
Use of this option results in a performance
penalty.

MTINITBUFFER
Writes misaligned data into the newly allocated
buffer. 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
buffer. The pattern used is 0xbaddcafe. Use of this
option results in a performance penalty.

MTCHUNKSIZE
This option changes the size of allocated memory
when a pool has exhausted all available memory in
the buffer. 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.

RETURN VALUES

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.

ERRORS

The malloc() and realloc() functions will fail if:

ENOMEM
The physical limits of the system are exceeded by size
bytes of memory which cannot be allocated.

EAGAIN
There is not enough memory available to allocate size bytes
of memory; but the application could try again later.

USAGE

Comparative features of the various allocation libraries can be found
in the umem_alloc(3MALLOC) manual page.

ATTRIBUTES

WARNINGS

Undefined results will occur if the size requested for a block of
memory exceeds the maximum size of a process's heap. This information
may be obtained using getrlimit().

March 21, 2005 MTMALLOC(3MALLOC)