MPI_Test - Tests for the completion of a specific send or receive.
17.2.370.1.1. C Syntax
#include <mpi.h> int MPI_Test(MPI_Request *request, int *flag, MPI_Status *status)
17.2.370.1.2. 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
17.2.370.1.3. 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
17.2.370.2. INPUT PARAMETER
request: Communication request (handle).
17.2.370.3. OUTPUT PARAMETERS
flag: True if operation completed (logical).
status: Status object (status).
IERROR: Fortran only: Error status (integer).
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 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.
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument.
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 errors 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.