umem_alloc(3MALLOC)

NAME
umem_alloc, umem_zalloc, umem_free, umem_nofail_callback - fast, scalable 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 determines 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_callback()) 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_CALLBACK_EXIT(status), one will call exit() while the other blocks until exit() terminates the program.

        o   invoking a context-changing function ( setcontext(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 responsible 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 multithreaded applications, callbacks are expected to perform 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 are as described in malloc(3C). The libumem library provides these functions for backwards-compatibility with the standard functions.

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. Unrecognized options are ignored. The options that are supported 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.

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:

MT-LevelMT-Safe

The malloc(), calloc(), free(), realloc(), and valloc() functions are Standard. The memalign() function is Stable. The umem_alloc(), umem_zalloc(), umem_free(), and umem_nofail_callback() functions are Evolving.

SEE ALSO

exit(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)

WARNINGS

Any of the following can cause undefined results:

    o   Passing a pointer returned from umem_alloc() or umem_zalloc() to free() or realloc().

    o   Passing a pointer returned from malloc(), calloc(), valloc(), 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) handler.

If the UMEM_NOFAIL callback performs UMEM_NOFAIL allocations, infinite recursion can occur.

NOTES

The following list compares the features of the malloc(3C), bsdmalloc(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).