aio_cancel - cancel an asynchronous I/O request (REALTIME)
#include <aio.h> int aio_cancel(int fildes, struct aiocb *aiocbp);
The aio_cancel() function attempts to cancel one or more asynchronous I/O requests currently outstanding against file descriptor fildes. The aiocbp argument points to the asynchronous I/O control block for a particular request to be canceled. If aiocbp is NULL, then all outstanding cancelable asynchronous I/O requests against fildes are canceled.
Normal asynchronous notification occurs for asynchronous I/O operations that are successfully canceled. If there are requests that cannot be canceled, then the normal asynchronous completion process takes place for those requests when they are completed.
For requested operations that are successfully canceled, the associated error status is set to [ECANCELED] and the return status is -1. For requested operations that are not successfully canceled, the aiocbp is not modified by aio_cancel().
If aiocbp is not NULL, then if fildes does not have the same value as the file descriptor with which the asynchronous operation was initiated, unspecified results occur.
Which operations are cancelable is implementation-dependent.
The aio_cancel() function returns the value AIO_CANCELED to the calling process if the requested operation(s) were canceled. The value AIO_NOTCANCELED is returned if at least one of the requested operation(s) cannot be canceled because it is in progress. In this case, the state of the other operations, if any, referenced in the call to aio_cancel() is not indicated by the return value of aio_cancel(). The application may determine the state of affairs for these operations by using aio_error(). The value AIO_ALLDONE is returned if all of the operations have already completed. Otherwise, the function returns -1 and sets errno to indicate the error.
The aio_cancel() function will fail if:
- The fildes argument is not a valid file descriptor.
- The aio_cancel() function is not supported by this implementation.
Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)