aio_write(2) aio_write(2)
NAME [Toc] [Back]
aio_write() - start asynchronous write operation
SYNOPSIS [Toc] [Back]
#include <aio.h>
int aio_write(struct aiocb *aiocbp);
DESCRIPTION [Toc] [Back]
The aio_write() function allows the calling process to perform an
asynchronous write to a previously opened file. The function call
returns when the write operation has been enqueued for processing. At
this point, processing of the write operation may proceed concurrently
with execution of the calling process or thread.
If an error condition is detected that prevents the write request from
being enqueued, aio_write() returns -1 and sets errno to indicate the
cause of the failure. Once the write operation has been successfully
enqueued, an aio_error() and aio_return() function referencing the
aiocb referred to by aiocbp must be used to determine its status and
any error conditions, including those normally reported by write().
The request remains enqueued and consumes process and system resources
until aio_return() is called.
The aio_write() function allows the calling process to write aiocbp-
>aio_nbytes to the file associated with aiocbp->aio_fildes from the
buffer pointed to by aiocbp->aio_buf. The priority of the write
operation is reduced by the value of aiocbp->aio_reqprio, which must
be a value between 0 (zero) and a maximum value which can be obtained
using the sysconf() call with the argument _SC_AIO_PRIO_DELTA_MAX. A
value of 0 (zero) yields no reduction in priority. The
aiocbp->aio_lio_opcode field is ignored.
When the O_APPEND flag is not set for the file, the write operation
takes place at the absolute position in the file given by aiocbp-
>aio_offset, as if lseek() were called immediately prior to the
operation with offset equal to aiocbp->aio_offset and whence set to
SEEK_SET. When the O_APPEND flag is set for the file, aiocbp-
>aio_offset is ignored, and asynchronous write operations append to
the file in the same order as the requests were enqueued. The value
of the file offset is never changed by asynchronous I/O operations.
Deallocating or altering the contents of memory referred to by aiocbp
while an asynchronous write operation is outstanding (i.e. before
aio_return() has been called) may produce unpredictable results.
If aiocbp->aio_sigevent is a valid signal event structure, then the
designated signal will be delivered when the requested asynchronous
write operation completes.
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aio_write(2) aio_write(2)
To use this function, link in the realtime library by specifying -lrt
on the compiler or linker command line.
RETURN VALUE [Toc] [Back]
aio_write() returns the following values:
0 Successful completion, the operation has been enqueued.
-1 Failure. The requested operation was not enqueued. errno
is set to indicate the error.
The return value from aio_write() reflects the success or failure of
enqueuing the requested write operation for asynchronous processing.
aio_write() fails if an error in the function call is immediately
detected, or if system resource limits prevent the request from being
enqueued. All other error conditions are reported asynchronously and
must be retrieved with aio_error() and aio_return().
ERRORS [Toc] [Back]
If aio_write() detects one of the following error conditions, errno is
set to the indicated value:
[EAGAIN] The request could not be queued either because of
a resource shortage or because the per-process or
system-wide limit on asynchronous I/O operations
or asynchronous threads would have been exceeded.
[EEXIST] The aiocbp is already in use for another
asynchronous I/O operation.
Once the write request has been enqueued by aio_write(), the following
errors, in addition to all of the errors normally reported by the
write() function, may be reported asynchronously by a subsequent call
to aio_error() or aio_return() referencing its aiocb.
[EBADF] The aiocbp->aio_fildes was not a valid file
descriptor open for writing.
[EINVAL] The aiocb->aio_sigevent is not a valid address in
the process virtual address space.
[EINVAL] The parameters of the indicated sigevent in
aiocb->aio_sigevent are invalid.
[EINVAL] The value of aiocbp->aio_reqprio is not valid.
[EINVAL] The value of aiocbp->aio_nbytes is invalid.
[EINVAL] The file offset implied by aiocbp->aio_offset or
aiocbp->aio_offset+ aiocbp->aio_nbytes are not
valid for the file at the time the request is
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aio_write(2) aio_write(2)
processed.
[ECANCELED] The write operation was canceled due to a
subsequent call to aio_cancel() referencing the
same aiocb that was used to start the operation.
EXAMPLES [Toc] [Back]
The following code sequence and call to aio_write() starts an
asynchronous write operation.
#include <fcntl.h>
#include <errno.h>
#include <aio.h>
char buf[4096];
int retval; ssize_t nbytes;
struct aiocb myaiocb;
bzero( &myaiocb, sizeof (struct aiocb));
bzero( &buf, sizeof (buf));
myaiocb.aio_fildes = open( "/dev/null", O_RDWR);
myaiocb.aio_offset = 0;
myaiocb.aio_buf = (void *) buf;
myaiocb.aio_nbytes = sizeof (buf);
myaiocb.aio_sigevent.sigev_notify = SIGEV_NONE;
retval = aio_write( &myaiocb );
if (retval) perror("aio_write:");
/* continue processing */
...
/* wait for completion */
while ( (retval = aio_error( &myaiocb) ) == EINPROGRESS) ;
/* free the aiocb */
nbytes = aio_return( &myaiocb);
SEE ALSO [Toc] [Back]
aio_cancel(2), aio_error(2), aio_fsync(2), aio_read(2), aio_return(2),
aio_suspend(2), lio_listio(2), write(2), aio(5).
STANDARDS CONFORMANCE [Toc] [Back]
aio_write(): POSIX Realtime Extensions, IEEE Std 1003.1b
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