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()
- 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