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MPI_Test(3OpenMPI)                                                                        MPI_Test(3OpenMPI)



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  communica-tion communication
       tion object was created by a nonblocking send or receive, then it is deallocated and the request han-dle handle
       dle 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 oper-ation operation
       ation  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 opera-tion operation
       tion 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  sta-tus.MPI_ERROR status.MPI_ERROR
       tus.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  han-dler handler
       dler  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




Open MPI 1.2                                   September 2006                             MPI_Test(3OpenMPI)