| UMEM_ALLOC(3MALLOC) | Memory Allocation Library Functions | UMEM_ALLOC(3MALLOC) |
umem_alloc, umem_zalloc, umem_free, umem_nofail_callback - fast, scalable memory allocation
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);
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
UMEM_NOFAIL
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 as described in malloc(3C). The libumem library provides these functions for backwards-compatibility with the standard functions.
See umem_debug(3MALLOC) for environment variables that effect the debugging features of the libumem library.
UMEM_OPTIONS
backend=sbrk
backend=mmap
perthread_cache=size
allocator=best
allocator=first
allocator=instant
allocator=next
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);
}
...
See attributes(7) 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 standards(7).
exit(2), mmap(2), sbrk(2), longjmp(3C), malloc(3C), pthread_exit(3C), thr_exit(3C), libumem(3LIB), bsdmalloc(3MALLOC), malloc(3MALLOC), mapmalloc(3MALLOC), umem_cache_create(3MALLOC), umem_debug(3MALLOC), watchmalloc(3MALLOC), attributes(7), standards(7)
Modular Debugger Guide:
https://illumos.org/books/mdb/
Any of the following can cause undefined results:
If the UMEM_NOFAIL callback performs UMEM_NOFAIL allocations, infinite recursion can occur.
The following list compares the features of the malloc(3C), bsdmalloc(3MALLOC), malloc(3MALLOC), mtmalloc(3MALLOC) , and the libumem functions.
| December 9, 2017 | OmniOS |