UMEM_ALLOC(3MALLOC)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 func‐
tion 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
backend=mmap
Set the underlying function used to
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.
perthread_cache=size
libumem allows for each thread to cache
recently freed small allocations for
future allocations. The size argument,
which accepts k, m, g, and t, suffixes
denotes the maximum amount of memory
each thread can use for this purpose.
The default amount used is 1 MB. Any
buffers in the per-thread cache are
freed when the thread exits. The effi‐
cacy of the per-thread cache can be
determined with the ::umastat mdb(1)
dcmd debugger command.
allocator=best
allocator=first
allocator=instant
allocator=next
Set the underlying allocation strategy.
The best fit strategy tells libumem to
use the smallest free segment possible.
The instant fit strategy approximates
the best fit strategy in constant cpu
time. The first fit strategy takes the
first free segment that can honor the
allocation. The next fit strategy uses
the next free segment after the previ‐
ously allocated one.
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).
Mar 24, 2008 UMEM_ALLOC(3MALLOC)