асинхронное чтение из файла (asynchronous read from a file)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
aio_read — asynchronous read from a file
Синопсис (Synopsis)
#include <aio.h>
int aio_read(struct aiocb *aiocbp);
Описание (Description)
The aio_read() function shall read aiocbp->aio_nbytes from the
file associated with aiocbp->aio_fildes into the buffer pointed
to by aiocbp->aio_buf. The function call shall return when the
read request has been initiated or queued to the file or device
(even when the data cannot be delivered immediately).
If prioritized I/O is supported for this file, then the
asynchronous operation shall be submitted at a priority equal to
a base scheduling priority minus aiocbp->aio_reqprio. If Thread
Execution Scheduling is not supported, then the base scheduling
priority is that of the calling process;
otherwise, the base scheduling priority is that of the calling
thread.
The aiocbp value may be used as an argument to aio_error() and
aio_return() in order to determine the error status and return
status, respectively, of the asynchronous operation while it is
proceeding. If an error condition is encountered during queuing,
the function call shall return without having initiated or queued
the request. The requested operation takes place at the absolute
position in the file as given by aio_offset, as if lseek() were
called immediately prior to the operation with an offset equal to
aio_offset and a whence equal to SEEK_SET. After a successful
call to enqueue an asynchronous I/O operation, the value of the
file offset for the file is unspecified.
The aio_sigevent member specifies the notification which occurs
when the request is completed.
The aiocbp->aio_lio_opcode field shall be ignored by aio_read().
The aiocbp argument points to an aiocb structure. If the buffer
pointed to by aiocbp->aio_buf or the control block pointed to by
aiocbp becomes an illegal address prior to asynchronous I/O
completion, then the behavior is undefined.
Simultaneous asynchronous operations using the same aiocbp
produce undefined results.
If synchronized I/O is enabled on the file associated with
aiocbp->aio_fildes, the behavior of this function shall be
according to the definitions of synchronized I/O data integrity
completion and synchronized I/O file integrity completion.
For any system action that changes the process memory space while
an asynchronous I/O is outstanding to the address range being
changed, the result of that action is undefined.
For regular files, no data transfer shall occur past the offset
maximum established in the open file description associated with
aiocbp->aio_fildes.
Возвращаемое значение (Return value)
The aio_read() function shall return the value zero if the I/O
operation is successfully queued; otherwise, the function shall
return the value -1 and set errno to indicate the error.
Ошибки (Error)
The aio_read() function shall fail if:
EAGAIN The requested asynchronous I/O operation was not queued
due to system resource limitations.
Each of the following conditions may be detected synchronously at
the time of the call to aio_read(), or asynchronously. If any of
the conditions below are detected synchronously, the aio_read()
function shall return -1 and set errno to the corresponding
value. If any of the conditions below are detected
asynchronously, the return status of the asynchronous operation
is set to -1, and the error status of the asynchronous operation
is set to the corresponding value.
EBADF The aiocbp->aio_fildes argument is not a valid file
descriptor open for reading.
EINVAL The file offset value implied by aiocbp->aio_offset would
be invalid,
aiocbp->aio_reqprio is not a valid value, or
aiocbp->aio_nbytes is an invalid value.
In the case that the aio_read() successfully queues the I/O
operation but the operation is subsequently canceled or
encounters an error, the return status of the asynchronous
operation is one of the values normally returned by the read()
function call. In addition, the error status of the asynchronous
operation is set to one of the error statuses normally set by the
read() function call, or one of the following values:
EBADF The aiocbp->aio_fildes argument is not a valid file
descriptor open for reading.
ECANCELED
The requested I/O was canceled before the I/O completed
due to an explicit aio_cancel() request.
EINVAL The file offset value implied by aiocbp->aio_offset would
be invalid.
The following condition may be detected synchronously or
asynchronously:
EOVERFLOW
The file is a regular file, aiobcp->aio_nbytes is greater
than 0, and the starting offset in aiobcp->aio_offset is
before the end-of-file and is at or beyond the offset
maximum in the open file description associated with
aiocbp->aio_fildes.
The following sections are informative.
Примеры (Examples)
None.
Использование в приложениях (Application usage)
None.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
aio_cancel(3p), aio_error(3p), lio_listio(3p), aio_return(3p),
aio_write(3p), close(3p), exec(1p), exit(3p), fork(3p),
lseek(3p), read(3p)
The Base Definitions volume of POSIX.1‐2017, aio.h(0p)
