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.
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