The Great and Terrible implementation of MPI-2

function index


Tests for the completion of all previously initiated requests
int MPI_Testall(
  int count,
  MPI_Request array_of_requests[],
  int *flag,
  MPI_Status array_of_statuses[]


[in] lists length (integer)
[in] array of requests (array of handles)
[out] True if all requests have completed; false otherwise (logical)
[out] array of status objects (array of Status). May be MPI_STATUSES_IGNORE.


Returns flag = true if all communications associated with active handles in the array have completed (this includes the case where no handle in the list is active). In this case, each status entry that corresponds to an active handle request is set to the status of the corresponding communication; if the request was allocated by a nonblocking communication call then it is deallocated, and the handle is set to MPI_REQUEST_NULL. Each status entry that corresponds to a null or inactive handle is set to empty.

Otherwise, flag = false is returned, no request is modified and the values of the status entries are undefined. This is a local operation.

Errors that occurred during the execution of MPI_TESTALL are handled as errors in MPI_WAITALL.

flag is true only if all requests have completed. Otherwise, flag is false and neither the array_of_requests nor the array_of_statuses is modified.

If one or more of the requests completes with an error, MPI_ERR_IN_STATUS is returned. An error value will be present is elements of array_of_status associated with the requests. Likewise, the MPI_ERROR field in the status elements associated with requests that have successfully completed will be MPI_SUCCESS. Finally, those requests that have not completed will have a value of MPI_ERR_PENDING.

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.
The actual error value is in the MPI_Status argument. This error class is returned only from the multiple-completion routines (MPI_Testall, MPI_Testany, MPI_Testsome, MPI_Waitall, MPI_Waitany, and MPI_Waitsome). The field MPI_ERROR in the status argument contains the error value or MPI_SUCCESS (no error and complete) or MPI_ERR_PENDING to indicate that the request has not completed.
The MPI Standard does not specify what the result of the multiple completion routines is when an error occurs. For example, in an MPI_WAITALL, does the routine wait for all requests to either fail or complete, or does it return immediately (with the MPI definition of immediately, which means independent of actions of other MPI processes)? MPICH has chosen to make the return immediate (alternately, local in MPI terms), and to use the error class MPI_ERR_PENDING (introduced in MPI 1.1) to indicate which requests have not completed. In most cases, only one request with an error will be detected in each call to an MPI routine that tests multiple requests. The requests that have not been processed (because an error occured in one of the requests) will have their MPI_ERROR field marked with MPI_ERR_PENDING.
Invalid MPI_Request. Either null or, in the case of a MPI_Start or MPI_Startall, not a persistent request.
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_Testall.

#include "mpi.h"
#include <stdio.h>
#include <windows.h>
int main(int argc, char *argv[])
    int rank, size, flag, i;
int buffer[100];
    MPI_Request r[4];
    MPI_Status status[4];

    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]);
        flag = 0;
        MPI_Testall(size-1, r, &flag, status);
        while (!flag)
            MPI_Testall(size-1, r, &flag, status);
        MPI_Send(buffer, 1, MPI_INT, 0, 123, MPI_COMM_WORLD);
return 0;