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

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_TEST(REQUEST, FLAG, STATUS, IERROR)
            LOGICAL   FLAG
            INTEGER   REQUEST, STATUS(MPI_STATUS_SIZE), IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Test(request, flag, status, ierror)
            TYPE(MPI_Request), INTENT(INOUT) :: request
            LOGICAL, INTENT(OUT) :: flag
            TYPE(MPI_Status) :: status
            INTEGER, OPTIONAL, INTENT(OUT) :: 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