The Great and Terrible implementation of MPI-2

function index


Tests to see if a request was cancelled
int MPI_Test_cancelled(
  MPI_Status *status,
  int *flag


[in] status object (Status)
[out] true if the request was cancelled, false otherwise (logical)


Returns flag = true if the communication associated with the status object was canceled successfully. In such a case, all other fields of status (such as count or tag) are undefined. Returns flag = false, otherwise. If a receive operation might be canceled then one should call MPI_TEST_CANCELLED first, to check whether the operation was canceled, before checking on the other fields of the return status.

Advice to users.

Cancel can be an expensive operation that should be used only exceptionally.

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

No error; MPI routine completed successfully.
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).

Example Code

The following sample code illustrates MPI_Test_cancelled.

#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
/* Test of various send cancel calls */
int main( int argc, char *argv[] )
int errs = 0;
int rank, size, source, dest;
    MPI_Comm comm;
    MPI_Status status;
    MPI_Request req;
static int bufsizes[4] = { 1, 100, 10000, 1000000 };
char *buf;
int cs, flag, n;

    MPI_Init( &argc, &argv );
    comm = MPI_COMM_WORLD;
    MPI_Comm_rank( comm, &rank );
    MPI_Comm_size( comm, &size );
    source = 0;
    dest = size - 1;

for (cs=0; cs<4; cs++) {
if (rank == 0) {
            n = bufsizes[cs];
            buf = (
char *)malloc( n );
if (!buf) {
                fprintf( stderr, "Unable to allocate %d bytes\n", n );fflush(stderr);
                MPI_Abort( MPI_COMM_WORLD, 1 );
            MPI_Isend( buf, n, MPI_CHAR, dest, cs+n+1, comm, &req );
            MPI_Cancel( &req );
            MPI_Wait( &req, &status );
            MPI_Test_cancelled( &status, &flag );
if (!flag) {
                errs ++;
                printf( "Failed to cancel a Isend request\n" );
                n = 0;
/* Send the size, zero for successfully cancelled */
MPI_Send( &n, 1, MPI_INT, dest, 123, comm );
/* Send the tag so the message can be received */
n = cs+n+1;
            MPI_Send( &n, 1, MPI_INT, dest, 123, comm );
            free( buf );
else if (rank == dest)
int n, tag;
char *btemp;
            MPI_Recv( &n, 1, MPI_INT, 0, 123, comm, &status );
            MPI_Recv( &tag, 1, MPI_INT, 0, 123, comm, &status );
if (n > 0)
/* If the message was not cancelled, receive it here */
                btemp = (char*)malloc( n );
if (!btemp)
                    fprintf( stderr, "Unable to allocate %d bytes\n", n);fflush(stderr);
                    MPI_Abort( MPI_COMM_WORLD, 1 );
                MPI_Recv( btemp, n, MPI_CHAR, 0, tag, comm, &status );
        MPI_Barrier( comm );

return 0;