The aio_cancel() function shall attempt 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 shall be canceled.
Normal asynchronous notification shall occur for asynchronous I/O operations
that are successfully canceled. If there are requests that cannot be canceled,
then the normal asynchronous completion process shall take place for those
requests when they are completed.
For requested operations that are successfully canceled, the associated error
status shall be set to [ECANCELED] and the return status shall be -1. For
requested operations that are not successfully canceled, the aiocbp
shall not be 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-defined.
The aio_cancel() function shall return the value AIO_CANCELED to the
calling process if the requested operation(s) were canceled. The value
AIO_NOTCANCELED shall be 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 shall return -1 and set errno to indicate the error.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html