count - number of requests in array (integer)
request_array - array of requests to check (array of handles)
index - index of first completed request (integer)
status - status of first completed request (structure)
The MPI_Waitany() function is used to wait for a request in an array of requests to complete.
The index of the first completed request will be stored in index . If that request is a receive, then the original tag and source of a recieved message are stored in the MPI_TAG and MPI_SOURCE fields of status respectively. If the received message has been truncated then MPI_ERROR will be set to be MPI_ERR_TRUNCATE. One additional field holds the total size of the message in bytes. If either a send or receive is successfully cancelled, then MPI_ERROR will contain MPI_ERR_CANCEL. Otherwise, it will be set to MPI_ERR_SUCCESS. If status is MPI_STATUS_IGNORE then this information will not be stored.
Only the first completed request is marked done, and will have a status output. The other requests are untouched, and can be completed in another call to a test or wait function.
The C++ version of this function passes the index of the completed request as the return value.
PMPI_Waitany() is the profiling version of this function.
All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.
In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.
MPI_SUCCESS - No error;
MPI_ERR_PENDING - Pending exception;
MPI_COUNT - Invalid array size;
MPI_ERR_ARG - Invalid pointer;
MPI_ERR_REQUEST - Invalid request.
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