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[])
- 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++ functions 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_WAITANY 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