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MPI_Testsome(3) man page (version 1.10.1)

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MPI_Testsome - Tests for completion of one or more previously initiated communications in a list.


C Syntax

#include <mpi.h>
int MPI_Testsome(int incount, MPI_Request array_of_requests[],
    int *outcount, int array_of_indices[], MPI_Status array_of_statuses[])

Fortran Syntax

INCLUDE ’mpif.h’

C++ Syntax

#include <mpi.h>
static int Request::Testsome(int incount, Request
    array_of_requests[], int array_of_indices[], Status array_of_statuses[])

static int Request::Testsome(int incount, Request
    array_of_requests[], int array_of_indices[])

Input Parameters

Length of array_of_requests (integer).
Array of requests (array of handles).

Output Parameters

Number of completed requests (integer).
Array of indices of operations that completed (array of integers).
Array of status objects for operations that completed (array of status).
Fortran only: Error status (integer).


Behaves like MPI_Waitsome, except that it returns immediately. If no operation has completed it returns outcount = 0. If there is no active handle in the list, it returns outcount = MPI_UNDEFINED.

MPI_Testsome is a local operation, which returns immediately, whereas MPI_Waitsome blocks until a communication completes, if it was passed a list that contains at least one active handle. Both calls fulfill a fairness requirement: If a request for a receive repeatedly appears in a list of requests passed to MPI_Waitsome or MPI_Testsome, and a matching send has been posted, then the receive will eventually succeed unless the send is satisfied by another receive; send requests also fulfill this fairness requirement.

Errors that occur during the execution of MPI_Testsome are handled as for MPI_Waitsome.

If your application does not need to examine the array_of_statuses field, you can save resources by using the predefined constant MPI_STATUSES_IGNORE can be used as a special value for the array_of_statuses argument.


The use of MPI_Testsome is likely to be more efficient than the use of MPI_Testany. The former returns information on all completed communications; with the latter, a new call is required for each communication that completes.

A server with multiple clients can use MPI_Waitsome so as not to starve any client. Clients send messages to the server with service requests. The server calls MPI_Waitsome with one receive request for each client, then handles all receives that have completed. If a call to MPI_Waitany is used instead, then one client could starve while requests from another client always sneak in first.


For each invocation of MPI_Testsome, if one or more requests generate an MPI exception, only the first MPI request that caused an exception will be passed to its corresponding error handler. No other error handlers will be invoked (even if multiple requests generated exceptions). However, all requests that generate an exception will have a relevant error code set in the corresponding status.MPI_ERROR field (unless MPI_STATUSES_IGNORE was used).

The default 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 MPI 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.

If the invoked error handler allows MPI_Testsome to return to the caller, the value MPI_ERR_IN_STATUS will be returned in the C and Fortran bindings. In C++, if the predefined error handler MPI::ERRORS_THROW_EXCEPTIONS is used, the value MPI::ERR_IN_STATUS will be contained in the MPI::Exception object. The MPI_ERROR field can then be examined in the array of returned statuses to determine exactly which request(s) generated an exception.

See Also


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