illumos: 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)