The Great and Terrible implementation of MPI-2

function index


Tests for completion of any previdously initiated requests
int MPI_Testany(
  int count,
  MPI_Request array_of_requests[],
  int *index,
  int *flag,
  MPI_Status *status


[in] list length (integer)
[in] array of requests (array of handles)
[out] index of operation that completed, or MPI_UNDEFINED if none completed (integer)
[out] true if one of the operations is complete (logical)
[out] status object (Status). May be MPI_STATUS_IGNORE.


Tests for completion of either one or none of the operations associated with active handles. In the former case, it returns flag = true, returns in index the index of this request in the array, and returns in status the status of that operation; if the request was allocated by a nonblocking communication call then the request is deallocated and the handle is set to MPI_REQUEST_NULL. (The array is indexed from zero in C, and from one in Fortran.) In the latter case (no operation completed), it returns flag = false, returns a value of MPI_UNDEFINED in index and status is undefined.

The array may contain null or inactive handles. If the array contains no active handles then the call returns immediately with flag = true, index = MPI_UNDEFINED, and an empty status.

If the array of requests contains active handles then the execution of MPI_TESTANY(count, array_of_requests, index, status) has the same effect as the execution of MPI_TEST( &array_of_requests[i], flag, status), for i=0, 1 ,..., count-1, in some arbitrary order, until one call returns flag = true, or all fail. In the former case, index is set to the last value of i, and in the latter case, it is set to MPI_UNDEFINED. MPI_TESTANY with an array containing one active entry is equivalent to MPI_TEST.


The function MPI_TESTANY returns with flag = true exactly in those situations where the function MPI_WAITANY returns; both functions return in that case the same values in the remaining parameters. Thus, a blocking MPI_WAITANY can be easily replaced by a nonblocking MPI_TESTANY. The same relation holds for the other pairs of Wait and Test functions defined in this section.

While it is possible to list a request handle more than once in the array_of_requests, such an action is considered erroneous and may cause the program to unexecpectedly terminate or produce incorrect results.

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.

Note on status for send operations

For send operations, the only use of status is for MPI_Test_cancelled or in the case that there is an error, in which case the MPI_ERROR field of status will be set.

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.

Example Code

The following sample code illustrates MPI_Testany.

#include "mpi.h"
#include <stdio.h>
#include <windows.h>
int main(int argc, char *argv[])
int rank, size, flag, i, index;
    int buffer[100];
    MPI_Request r[4];
    MPI_Status status;
    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    if (size != 4)
        printf("Please run with 4 processes.\n");fflush(stdout);
        return 1;
    if (rank == 0)
        for (i=1; i<size; i++)
            MPI_Irecv(&buffer[i], 1, MPI_INT, i, 123, MPI_COMM_WORLD, &r[i-1]);
for (i=0; i<size-1; i++)
            flag = 0;
            MPI_Testany(size-1, r, &index, &flag, &status);
            while (!flag)
                MPI_Testany(size-1, r, &index, &flag, &status);
            printf("%d finished\n", index+1);
        MPI_Send(buffer, 1, MPI_INT, 0, 123, MPI_COMM_WORLD);
return 0;