MPI_Test(3)                        Open MPI                        MPI_Test(3)



NAME
       MPI_Test - Tests for the completion of a specific send or receive.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Test(MPI_Request *request, int *flag, MPI_Status *status)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_TEST(REQUEST, FLAG, STATUS, IERROR)
            LOGICAL   FLAG
            INTEGER   REQUEST, STATUS(MPI_STATUS_SIZE), IERROR


C++ Syntax
       #include <mpi.h>
       bool Request::Test(Status& status)

       bool Request::Test()


INPUT PARAMETER
       request   Communication request (handle).


OUTPUT PARAMETERS
       flag      True if operation completed (logical).

       status    Status object (status).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       A call to MPI_Test returns flag = true if the operation identified by
       request is complete. In such a case, the status object is set to
       contain information on the completed operation; if the communication
       object was created by a nonblocking send or receive, then it is
       deallocated and the request handle is set to MPI_REQUEST_NULL. The call
       returns flag = false, otherwise. In this case, the value of the status
       object is undefined. MPI_Test is a local operation.

       The return status object for a receive operation carries information
       that can be accessed as described in Section 3.2.5 of the MPI-1
       Standard, "Return Status." The status object for a send operation
       carries information that can be accessed by a call to
       MPI_Test_cancelled (see Section 3.8 of the MPI-1 Standard, "Probe and
       Cancel").

       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.

       One is allowed to call MPI_Test with a null or inactive request
       argument. In such a case the operation returns with flag = true and
       empty status.

       The functions MPI_Wait and MPI_Test can be used to complete both sends
       and receives.


NOTES
       The use of the nonblocking MPI_Test call allows the user to schedule
       alternative activities within a single thread of execution. An event-
       driven thread scheduler can be emulated with periodic calls to
       MPI_Test.


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_TEST 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_TEST 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_Testall
       MPI_Testany
       MPI_Testsome
       MPI_Wait
       MPI_Waitall
       MPI_Waitany
       MPI_Waitsome
       MPI_Win_set_errhandler




1.4.1                            Jan 14, 2010                      MPI_Test(3)
