Asynchronously write to a file
#include <aio.h> int aio_write( struct aiocb * aiocbptr ); int aio_write64( struct aiocb64 * aiocbptr );
- A pointer to an asynchronous I/O control block of type aiocb or aiocb64 that defines how much data to write, and where to write it.
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The aio_write() and aio_write64() functions asynchronously write aiocbptr->aio_nbytes to the file associated with aiocbptr->aio_fildes from the buffer that aiocbptr->aio_buf points to. The functions return when the write request has been initiated or, at a minimum, queued to the file or device.
The asynchronous operation is submitted at the scheduling priority of the thread minus aiocbptr->aio_reqprio.
If O_APPEND isn't set for the file descriptor aio_fildes, then the requested operation takes place at the absolute position in the file as given by aio_offset, as if lseek() were called immediately before the operation with an offset of aio_offset and a whence of SEEK_SET.
If O_APPEND is set for the file descriptor, write operations append to the file in the same order as the calls were made.
If synchronized I/O is enabled on the file associated with aiocbptr->aio_fildes, these functions behave in accordance with the definitions of synchronized I/O data integrity completion and synchronized I/O file integrity completion.
The following conditions may be detected synchronously at the time of the call to aio_write() or aio_write64(), or asynchronously. If any of these conditions are detected synchronously, these functions return -1 and set errno to the corresponding value. If any of these conditions 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:
- The aiocbptr->aio_fildes argument isn't a valid file descriptor that's open for writing.
- The file offset value implied by aiocbptr->aio_offset would be invalid, aiocbptr->aio_reqprio isn't a valid value, or aiocbptr->aio_nbytes is invalid.
If aio_write() or aio_write64() 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 write(). In addition, the error status of the asynchronous operation is set to one of the error statuses normally set by write(), or one of the following:
- The aiocbptr->aio_fildes isn't a valid file descriptor that's open for writing.
- The requested I/O was canceled before the I/O was completed, due to an explicit aio_cancel(), request.
- The file offset value implied by aiocbptr->aio_offset would be invalid.
The following condition may be detected synchronously or asynchronously:
- The file is a regular file, aiocbptr->aio_nbytes is greater than 0, and the starting offset in aiocbptr->aio_offset is at or beyond the offset maximum in the open file description associated with aiocbptr->aio_fildes.
0 if the I/O operation was successfully queued, or -1 if an error occurred ( errno is set).
- The requested asynchronous I/O operation wasn't queued because of system resource limitations.
The first time you call an aio_* function, a thread pool is created, making your process multithreaded if it isn't already. The thread pool isn't destroyed until your process ends.
Last modified: 2014-06-24