асинхронное чтение (asynchronous read)
Имя (Name)
aio_read - asynchronous read
Синопсис (Synopsis)
#include <aio.h>
int aio_read(struct aiocb *aiocbp);
Link with -lrt.
Описание (Description)
The aio_read() function queues the I/O request described by the
buffer pointed to by aiocbp. This function is the asynchronous
analog of read(2). The arguments of the call
read(fd, buf, count)
correspond (in order) to the fields aio_fildes, aio_buf, and
aio_nbytes of the structure pointed to by aiocbp. (See aio(7)
for a description of the aiocb structure.)
The data is read starting at the absolute position
aiocbp->aio_offset, regardless of the file offset. After the
call, the value of the file offset is unspecified.
The "asynchronous" means that this call returns as soon as the
request has been enqueued; the read may or may not have completed
when the call returns. One tests for completion using
aio_error(3). The return status of a completed I/O operation can
be obtained by aio_return(3). Asynchronous notification of I/O
completion can be obtained by setting aiocbp->aio_sigevent
appropriately; see sigevent(7) for details.
If _POSIX_PRIORITIZED_IO is defined, and this file supports it,
then the asynchronous operation is submitted at a priority equal
to that of the calling process minus aiocbp->aio_reqprio.
The field aiocbp->aio_lio_opcode is ignored.
No data is read from a regular file beyond its maximum offset.
Возвращаемое значение (Return value)
On success, 0 is returned. On error, the request is not
enqueued, -1 is returned, and errno is set to indicate the error.
If an error is detected only later, it will be reported via
aio_return(3) (returns status -1) and aio_error(3) (error status—
whatever one would have gotten in errno, such as EBADF).
Ошибки (Error)
EAGAIN Out of resources.
EBADF aio_fildes is not a valid file descriptor open for
reading.
EINVAL One or more of aio_offset, aio_reqprio, or aio_nbytes are
invalid.
ENOSYS aio_read() is not implemented.
EOVERFLOW
The file is a regular file, we start reading before end-
of-file and want at least one byte, but the starting
position is past the maximum offset for this file.
Версии (Versions)
The aio_read() function is available since glibc 2.1.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│aio_read() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008.
Примечание (Note)
It is a good idea to zero out the control block before use. The
control block must not be changed while the read operation is in
progress. The buffer area being read into must not be accessed
during the operation or undefined results may occur. The memory
areas involved must remain valid.
Simultaneous I/O operations specifying the same aiocb structure
produce undefined results.
Примеры (Examples)
See aio(7).
Смотри также (See also)
aio_cancel(3), aio_error(3), aio_fsync(3), aio_return(3),
aio_suspend(3), aio_write(3), lio_listio(3), aio(7)
