openmpi/ompi/mpi/man/man3/MPI_Testsome.3

.\"Copyright 2006, Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.TH MPI_Testsome 3OpenMPI "September 2006" "Open MPI 1.2" " "
.SH NAME
\fBMPI_Testsome\fP \- Tests for completion of one or more previously initiated communications in a list. 

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Testsome(int \fIincount\fP, MPI_Request \fI*array_of_requests\fP,
	int\fI *outcount\fP, int\fI *array_of_indices\fP, MPI_Status\fI *array_of_statuses\fP)

.SH Fortran Syntax
.nf
INCLUDE 'mpif.h'
MPI_TESTSOME(\fIINCOUNT, ARRAY_OF_REQUESTS, OUTCOUNT,
		ARRAY_OF_INDICES, ARRAY_OF_STATUSES, IERROR\fP)
	INTEGER	\fIINCOUNT, ARRAY_OF_REQUESTS(*)\fP
	INTEGER	\fIOUTCOUNT, ARRAY_OF_INDICES(*)\fP
	INTEGER	\fIARRAY_OF_STATUSES(MPI_STATUS_SIZE,*), IERROR\fP 

.SH C++ Syntax
.nf
#include <mpi.h>
static int Request::Testsome(int \fIincount\fP, Request 
	\fIarray_of_requests\fP[], int \fIarray_of_indices\fP[], Status \fIarray_of_statuses\fP[]) 

static int Request::Testsome(int \fIincount\fP, Request 
	\fIarray_of_requests\fP[], int \fIarray_of_indices\fP[]) 

.SH INPUT PARAMETERS
.ft R
.TP 1i
incount
Length of array_of_requests (integer).
.TP 1i
array_of_requests
Array of requests (array of handles).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
outcount
Number of completed requests (integer).
.TP 1i
array_of_indices
Array of indices of operations that completed (array of integers).
.TP 1i
array_of_statuses
Array of status objects for operations that completed (array of status).
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer). 

.SH DESCRIPTION
.ft R
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.  
.sp
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.
.sp
Errors that occur during the execution of MPI_Testsome are handled as for
MPI_Waitsome. 
.sp
If your application does not need to examine the \fIarray_of_statuses\fP field, you can save resources by using the predefined constant MPI_STATUSES_IGNORE can be used as a special value for the \fIarray_of_statuses\fP argument. 

.SH 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. 
.sp
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. 

.SH ERRORS
For each invocation of MPI_Testsome, if one or more requests generate
an MPI exception, only the \fIfirst\fP 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, \fIall\fP requests that generate an exception
will have a relevant error code set in the corresponding
status.MPI_ERROR field (unless MPI_IGNORE_STATUSES was used).
.sp
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.
.sp
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.

.SH SEE ALSO
.ft R
.sp
MPI_Comm_set_errhandler
.br
MPI_File_set_errhandler
.br
MPI_Test
.br
MPI_Testall
.br
MPI_Testany
.br
MPI_Wait
.br
MPI_Waitall
.br
MPI_Waitany
.br
MPI_Waitsome
.br
MPI_Win_set_errhandler
.br