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

NAME

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

SYNTAX

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'
       MPI_TESTSOME(INCOUNT, ARRAY_OF_REQUESTS, OUTCOUNT,
                 ARRAY_OF_INDICES, ARRAY_OF_STATUSES, IERROR)
            INTEGER   INCOUNT, ARRAY_OF_REQUESTS(*)
            INTEGER   OUTCOUNT, ARRAY_OF_INDICES(*)
            INTEGER   ARRAY_OF_STATUSES(MPI_STATUS_SIZE,*), IERROR

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

       incount   Length of array_of_requests (integer).

       array_of_requests
                 Array of requests (array of handles).

OUTPUT PARAMETERS

       outcount  Number of completed requests (integer).

       array_of_indices
                 Array of indices of operations that completed (array of integers).

       array_of_statuses
                 Array of status objects for operations that completed (array of status).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

Behaves like MPI_Waitsome, except that it returns immediately.

Returns in outcount the number of requests from the list array_of_requests that have completed. Returns
in the first outcount locations of the array array_of_indices the indices of these operations (index
within the array array_of_requests; the array is indexed from 0 in C and from 1 in Fortran). Returns in
the first outcount locations of the array array_of_status the status for these completed operations. If a
request that completed was allocated by a nonblocking communication call, then it is deallocated, and the
associated handle is set to MPI_REQUEST_NULL.

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.

NOTES

       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.

ERRORS

       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.