Node:Status of AIO Operations,
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Getting the Status of AIO Operations
As already described in the documentation of the functions in the last
section, it must be possible to get information about the status of an I/O
request. When the operation is performed truly asynchronously (as with
aio_read
and aio_write
and with aio_listio
when the
mode is LIO_NOWAIT
) one sometimes needs to know whether a
specific request already terminated and if yes, what the result was.
The following two functions allow you to get this kind of information.
int aio_error (const struct aiocb *aiocbp)
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Function |
This function determines the error state of the request described by the
struct aiocb variable pointed to by aiocbp. If the
request has not yet terminated the value returned is always
EINPROGRESS . Once the request has terminated the value
aio_error returns is either 0 if the request completed
successfully or it returns the value which would be stored in the
errno variable if the request would have been done using
read , write , or fsync .
The function can return ENOSYS if it is not implemented. It
could also return EINVAL if the aiocbp parameter does not
refer to an asynchronous operation whose return status is not yet known.
When the sources are compiled with _FILE_OFFSET_BITS == 64 this
function is in fact aio_error64 since the LFS interface
transparently replaces the normal implementation.
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int aio_error64 (const struct aiocb64 *aiocbp)
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Function |
This function is similar to aio_error with the only difference
that the argument is a reference to a variable of type struct
aiocb64 .
When the sources are compiled with _FILE_OFFSET_BITS == 64 this
function is available under the name aio_error and so
transparently replaces the interface for small files on 32 bit
machines.
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ssize_t aio_return (const struct aiocb *aiocbp)
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Function |
This function can be used to retrieve the return status of the operation
carried out by the request described in the variable pointed to by
aiocbp. As long as the error status of this request as returned
by aio_error is EINPROGRESS the return of this function is
undefined.
Once the request is finished this function can be used exactly once to
retrieve the return value. Following calls might lead to undefined
behaviour. The return value itself is the value which would have been
returned by the read , write , or fsync call.
The function can return ENOSYS if it is not implemented. It
could also return EINVAL if the aiocbp parameter does not
refer to an asynchronous operation whose return status is not yet known.
When the sources are compiled with _FILE_OFFSET_BITS == 64 this
function is in fact aio_return64 since the LFS interface
transparently replaces the normal implementation.
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int aio_return64 (const struct aiocb64 *aiocbp)
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Function |
This function is similar to aio_return with the only difference
that the argument is a reference to a variable of type struct
aiocb64 .
When the sources are compiled with _FILE_OFFSET_BITS == 64 this
function is available under the name aio_return and so
transparently replaces the interface for small files on 32 bit
machines.
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