umem_alloc(3MALLOC) Memory Allocation Library Functions umem_alloc(3MALLOC)NAME
umem_alloc, umem_zalloc, umem_free, umem_nofail_callback - fast, scal‐
able memory allocation
SYNOPSIS
cc [ flag ... ] file... -lumem [ library ... ]
#include <umem.h>
void *umem_alloc(size_t size, int flags);
void *umem_zalloc(size_t size, int flags);
void umem_free(void *buf, size_t size);
void umem_nofail_callback((int (*callback)(void));
void *malloc(size_t size);
void *calloc(size_t nelem, size_t elsize);
void free(void *ptr);
void *memalign(size_t alignment, size_t size);
void *realloc(void *ptr, size_t size);
void *valloc(size_t size);
DESCRIPTION
The umem_alloc() function returns a pointer to a block of size bytes
suitably aligned for any variable type. The initial contents of memory
allocated using umem_alloc() is undefined. The flags argument deter‐
mines the behavior of umem_alloc() if it is unable to fulfill the
request. The flags argument can take the following values:
UMEM_DEFAULT Return NULL on failure.
UMEM_NOFAIL Call an optional callback (set with umem_nofail_call‐
back()) on failure. The callback takes no arguments and
can finish by:
o returning UMEM_CALLBACK_RETRY, in which case
the allocation will be retried. If the
allocation fails, the callback will be
invoked again.
o returning UMEM_CALLBACK_EXIT(status), in
which case exit(2) is invoked with status as
its argument. The exit() function is called
only once. If multiple threads return from
the UMEM_NOFAIL callback with UMEM_CALL‐
BACK_EXIT(status), one will call exit()
while the other blocks until exit() termi‐
nates the program.
o invoking a context-changing function (set‐
context(2)) or a non-local jump (longjmp(3C)
or siglongjmp(3C), or ending the current
thread of control (thr_exit(3C) or
pthread_exit(3C). The application is respon‐
sible for any necessary cleanup. The state
of libumem remains consistent.
If no callback has been set or the callback has been
set to NULL, umem_alloc(..., UMEM_NOFAIL) behaves as
though the callback returned UMEM_CALLBACK_EXIT(255).
The libumem library can call callbacks from any place
that a UMEM_NOFAIL allocation is issued. In multi‐
threaded applications, callbacks are expected to per‐
form their own concurrency management.
The function call umem_alloc(0, flag) always returns NULL. The function
call umem_free(NULL, 0) is allowed.
The umem_zalloc() function has the same semantics as umem_alloc(), but
the block of memory is initialized to zeros before it is returned.
The umem_free() function frees blocks previously allocated using
umem_alloc() and umem_zalloc(). The buffer address and size must
exactly match the original allocation. Memory must not be returned
piecemeal.
The umem_nofail_callback() function sets the process-wide UMEM_NOFAIL
callback. See the description of UMEM_NOFAIL for more information.
The malloc(), calloc(), free(), memalign(), realloc(), and valloc()
functions are as described in malloc(3C). The libumem library provides
these functions for backwards-compatibility with the standard func‐
tions.
ENVIRONMENT VARIABLES
See umem_debug(3MALLOC) for environment variables that effect the
debugging features of the libumem library.
UMEM_OPTIONS Contains a list of comma-separated options. Unrecog‐
nized options are ignored. The options that are sup‐
ported are:
backend=sbrk Set the underlying function used to
backend=mmap allocate memory. This option can be set
to sbrk (the default) for an
sbrk(2)-based source or mmap for an
mmap(2)-based source. If set to a value
that is not supported, sbrk will be
used.
EXAMPLES
Example 1 Using the umem_alloc() function.
#include <stdio.h>
#include <umem.h>
...
char *buf = umem_alloc(1024, UMEM_DEFAULT);
if (buf == NULL) {
fprintf(stderr, "out of memory\n");
return (1);
}
/* cannot assume anything about buf's contents */
...
umem_free(buf, 1024);
...
Example 2 Using the umem_zalloc() function
#include <stdio.h>
#include <umem.h>
...
char *buf = umem_zalloc(1024, UMEM_DEFAULT);
if (buf == NULL) {
fprintf(stderr, "out of memory\n");
return (1);
}
/* buf contains zeros */
...
umem_free(buf, 1024);
...
Example 3 Using UMEM_NOFAIL
#include <stdlib.h>
#include <stdio.h>
#include <umem.h>
/*
* Note that the allocation code below does not have to
* check for umem_alloc() returning NULL
*/
int
my_failure_handler(void)
{
(void) fprintf(stderr, "out of memory\n");
return (UMEM_CALLBACK_EXIT(255));
}
...
umem_nofail_callback(my_failure_handler);
...
int i;
char *buf[100];
for (i = 0; i < 100; i++)
buf[i] = umem_alloc(1024 * 1024, UMEM_NOFAIL);
...
for (i = 0; i < 100; i++)
umem_free(buf[i], 1024 * 1024);
...
Example 4 Using UMEM_NOFAIL in a multithreaded application
#define _REENTRANT
#include <thread.h>
#include <stdio.h>
#include <umem.h>
void *
start_func(void *the_arg)
{
int *info = (int *)the_arg;
char *buf = umem_alloc(1024 * 1024, UMEM_NOFAIL);
/* does not need to check for buf == NULL */
buf[0] = 0;
...
/*
* if there were other UMEM_NOFAIL allocations,
* we would need to arrange for buf to be
* umem_free()ed upon failure.
*/
...
umem_free(buf, 1024 * 1024);
return (the_arg);
}
...
int
my_failure_handler(void)
{
/* terminate the current thread with status NULL */
thr_exit(NULL);
}
...
umem_nofail_callback(my_failure_handler);
...
int my_arg;
thread_t tid;
void *status;
(void) thr_create(NULL, NULL, start_func, &my_arg, 0,
NULL);
...
while (thr_join(0, &tid, &status) != 0)
;
if (status == NULL) {
(void) fprintf(stderr, "thread %d ran out of memory\n",
tid);
}
...
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Committed │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe │
├─────────────────────────────┼─────────────────────────────┤
│Standard │See below. │
└─────────────────────────────┴─────────────────────────────┘
For malloc(), calloc(), free(), realloc(), and valloc(), see stan‐
dards(5).
SEE ALSOexit(2), mmap(2), sbrk(2), bsdmalloc(3MALLOC), libumem(3LIB),
longjmp(3C), malloc(3C), malloc(3MALLOC), mapmalloc(3MALLOC),
pthread_exit(3C), thr_exit(3C), umem_cache_create(3MALLOC),
umem_debug(3MALLOC), watchmalloc(3MALLOC), attributes(5), standards(5)
Solaris Modular Debugger Guide
WARNINGS
Any of the following can cause undefined results:
o Passing a pointer returned from umem_alloc() or umem_zal‐
loc() to free() or realloc().
o Passing a pointer returned from malloc(), calloc(), val‐
loc(), memalign(), or realloc() to umem_free().
o Writing past the end of a buffer allocated using
umem_alloc() or umem_zalloc()
o Performing UMEM_NOFAIL allocations from an atexit(3C) han‐
dler.
If the UMEM_NOFAIL callback performs UMEM_NOFAIL allocations, infinite
recursion can occur.
NOTES
The following list compares the features of the malloc(3C), bsdmal‐
loc(3MALLOC), malloc(3MALLOC), mtmalloc(3MALLOC) , and the libumem
functions.
o The malloc(3C), bsdmalloc(3MALLOC), and malloc(3MALLOC)
functions have no support for concurrency. The libumem and
mtmalloc(3MALLOC) functions support concurrent allocations.
o The bsdmalloc(3MALLOC) functions afford better performance
but are space-inefficient.
o The malloc(3MALLOC) functions are space-efficient but have
slower performance.
o The standard, fully SCD-compliant malloc(3C) functions are a
trade-off between performance and space-efficiency.
o The mtmalloc(3MALLOC) functions provide fast, concurrent
malloc() implementations that are not space-efficient.
o The libumem functions provide a fast, concurrent allocation
implementation that in most cases is more space-efficient
than mtmalloc(3MALLOC).
SunOS 5.11 24 Mar 2008 umem_alloc(3MALLOC)