MPI_Waitany(3OpenMPI)													     MPI_Waitany(3OpenMPI)

NAME

       MPI_Waitany - Waits for any specified send or receive to complete.

SYNTAX

C Syntax
       #include <mpi.h>
       int MPI_Waitany(int count, MPI_Request *array_of_requests,
	    int *index, MPI_Status *status)

Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_WAITANY(COUNT, ARRAY_OF_REQUESTS, INDEX, STATUS, IERROR)
	    INTEGER   COUNT, ARRAY_OF_REQUESTS(*), INDEX
	    INTEGER   STATUS(MPI_STATUS_SIZE), IERROR

C++ Syntax
       #include <mpi.h>
       static int Request::Waitany(int count, Request
	    array_of_requests[], Status& status)

       static int Request::Waitany(int count, Request array_of_requests[])

INPUT PARAMETERS

       count	 List length (integer).

       array_of_requests
		 Array of requests (array of handles).

OUTPUT PARAMETERS

       index	 Index of handle for operation that completed (integer). In the range 0 to count-1.  In Fortran, the range is 1 to count.

       status	 Status object (status).

       IERROR	 Fortran only: Error status (integer).

DESCRIPTION

       A call to MPI_Waitany can be used to wait for the completion of one out of several requests.

       The  array_of_requests  list  may  contain  null  or  inactive handles. If the list contains no active handles (list has length zero or all
       entries are null or inactive), then the call returns immediately with index = MPI_UNDEFINED, and an empty status.

       The   execution	 of   MPI_Waitany(count,   array_of_requests,	index,	 status)   has	 the   same   effect   as   the    execution	of
       MPI_Wait(&array_of_requests[i],	status),  where i is the value returned by index (unless the value of index is MPI_UNDEFINED). MPI_Waitany
       with an array containing one active entry is equivalent to MPI_Wait.

       If your application does not need to examine the status field, you can save resources by using the predefined constant MPI_STATUS_IGNORE as
       a special value for the status argument.

       Example: Client-server code (starvation can occur).

	   CALL MPI_COMM_SIZE(comm, size, ierr)
	   CALL MPI_COMM_RANK(comm, rank, ierr)
	   IF(rank .GT 0) THEN	       ! client code
	       DO WHILE(.TRUE.)
		  CALL MPI_ISEND(a, n, MPI_REAL, 0, tag, comm, request, ierr)
		  CALL MPI_WAIT(request, status, ierr)
	       END DO
	   ELSE 	! rank=0 -- server code
		  DO i=1, size-1
		     CALL MPI_IRECV(a(1,i), n, MPI_REAL, i tag,
			      comm, request_list(i), ierr)
		  END DO
		  DO WHILE(.TRUE.)
		     CALL MPI_WAITANY(size-1, request_list, index, status, ierr)
		     CALL DO_SERVICE(a(1,index))  ! handle one message
		     CALL MPI_IRECV(a(1, index), n, MPI_REAL, index, tag,
			       comm, request_list(index), ierr)
		  END DO
	   END IF

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ func-
       tions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception  mechanism
       will be used to throw an MPI::Exception object.

       Before  the error value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed  with  MPI_Comm_set_errhandler,  MPI_File_set_errhandler,	or  MPI_Win_set_errhandler
       (depending on the type of MPI handle that generated the request); the predefined error handler MPI_ERRORS_RETURN may be used to cause error
       values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

       Note that per MPI-1 section 3.2.5, MPI exceptions on requests passed to MPI_WAITANY do not set the status.MPI_ERROR field in  the  returned
       status.	 The error code is passed to the back-end error handler and may be passed back to the caller through the return value of MPI_WAIT-
       ANY if the back-end error handler returns it.  The pre-defined MPI error handler MPI_ERRORS_RETURN exhibits this behavior, for example.

SEE ALSO

       MPI_Comm_set_errhandler
       MPI_File_set_errhandler
       MPI_Test
       MPI_Testall
       MPI_Testany
       MPI_Testsome
       MPI_Wait
       MPI_Waitall
       MPI_Waitsome
       MPI_Win_set_errhandler

Open MPI 1.2							  September 2006					     MPI_Waitany(3OpenMPI)