выделить выровненную память (allocate aligned memory)
Имя (Name)
posix_memalign, aligned_alloc, memalign, valloc, pvalloc -
allocate aligned memory
Синопсис (Synopsis)
#include <stdlib.h>
int posix_memalign(void **memptr, size_t alignment, size_t size);
void *aligned_alloc(size_t alignment, size_t size);
void *valloc(size_t size);
#include <malloc.h>
void *memalign(size_t alignment, size_t size);
void *pvalloc(size_t size);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
posix_memalign():
_POSIX_C_SOURCE >= 200112L
aligned_alloc():
_ISOC11_SOURCE
valloc():
Since glibc 2.12:
(_XOPEN_SOURCE >= 500) && !(_POSIX_C_SOURCE >= 200112L)
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500
Описание (Description)
The function posix_memalign() allocates size bytes and places the
address of the allocated memory in *memptr. The address of the
allocated memory will be a multiple of alignment, which must be a
power of two and a multiple of sizeof(void *). This address can
later be successfully passed to free(3). If size is 0, then the
value placed in *memptr is either NULL or a unique pointer value.
The obsolete function memalign() allocates size bytes and returns
a pointer to the allocated memory. The memory address will be a
multiple of alignment, which must be a power of two.
The function aligned_alloc() is the same as memalign(), except
for the added restriction that size should be a multiple of
alignment.
The obsolete function valloc() allocates size bytes and returns a
pointer to the allocated memory. The memory address will be a
multiple of the page size. It is equivalent to
memalign(sysconf(_SC_PAGESIZE),size).
The obsolete function pvalloc() is similar to valloc(), but
rounds the size of the allocation up to the next multiple of the
system page size.
For all of these functions, the memory is not zeroed.
Возвращаемое значение (Return value)
aligned_alloc(), memalign(), valloc(), and pvalloc() return a
pointer to the allocated memory on success. On error, NULL is
returned, and errno is set to indicate the error.
posix_memalign() returns zero on success, or one of the error
values listed in the next section on failure. The value of errno
is not set. On Linux (and other systems), posix_memalign() does
not modify memptr on failure. A requirement standardizing this
behavior was added in POSIX.1-2008 TC2.
Ошибки (Error)
EINVAL The alignment argument was not a power of two, or was not
a multiple of sizeof(void *).
ENOMEM There was insufficient memory to fulfill the allocation
request.
Версии (Versions)
The functions memalign(), valloc(), and pvalloc() have been
available since at least glibc 2.0.
The function aligned_alloc() was added to glibc in version 2.16.
The function posix_memalign() is available since glibc 2.1.91.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├───────────────────────────────┼───────────────┼────────────────┤
│aligned_alloc(), memalign(), │ Thread safety │ MT-Safe │
│posix_memalign() │ │ │
├───────────────────────────────┼───────────────┼────────────────┤
│valloc(), pvalloc() │ Thread safety │ MT-Unsafe init │
└───────────────────────────────┴───────────────┴────────────────┘
Стандарты (Conforming to)
The function valloc() appeared in 3.0BSD. It is documented as
being obsolete in 4.3BSD, and as legacy in SUSv2. It does not
appear in POSIX.1.
The function pvalloc() is a GNU extension.
The function memalign() appears in SunOS 4.1.3 but not in 4.4BSD.
The function posix_memalign() comes from POSIX.1d and is
specified in POSIX.1-2001 and POSIX.1-2008.
The function aligned_alloc() is specified in the C11 standard.
Headers
Everybody agrees that posix_memalign() is declared in <stdlib.h>.
On some systems memalign() is declared in <stdlib.h> instead of
<malloc.h>.
According to SUSv2, valloc() is declared in <stdlib.h>. Glibc
declares it in <malloc.h>, and also in <stdlib.h> if suitable
feature test macros are defined (see above).
Примечание (Note)
On many systems there are alignment restrictions, for example, on
buffers used for direct block device I/O. POSIX specifies the
pathconf(path,_PC_REC_XFER_ALIGN) call that tells what alignment
is needed. Now one can use posix_memalign() to satisfy this
requirement.
posix_memalign() verifies that alignment matches the requirements
detailed above. memalign() may not check that the alignment
argument is correct.
POSIX requires that memory obtained from posix_memalign() can be
freed using free(3). Some systems provide no way to reclaim
memory allocated with memalign() or valloc() (because one can
pass to free(3) only a pointer obtained from malloc(3), while,
for example, memalign() would call malloc(3) and then align the
obtained value). The glibc implementation allows memory obtained
from any of these functions to be reclaimed with free(3).
The glibc malloc(3) always returns 8-byte aligned memory
addresses, so these functions are needed only if you require
larger alignment values.
Смотри также (See also)
brk(2), getpagesize(2), free(3), malloc(3)
