MPI_Waitsome(3)

NAME
MPI_Waitsome - Waits for some given communications to complete

SYNOPSIS
#include <mpi.h>
int MPI_Waitsome(int count, MPI_Request* reqs, int *ndone,
                int *indices, MPI_Status *stats)

INPUT PARAMETERS
incount
    - length of array_of_requests (integer)
reqs
    - array of requests (array of handles)

OUTPUT PARAMETERS
ndone
    - number of completed requests (integer)
indices
    - array of indices of operations that completed (array of integers)
stats
    - array of status objects for operations that completed (array of Status), or the MPI constant MPI_STATUSES_IGNORE

NOTES

The array of indicies are in the range 0 to incount - 1 for C and in the range 1 to incount for Fortran.

Null requests are ignored; if all requests are null, then the routine returns with outcount set to MPI_UNDEFINED .

NOTE ON STATUS FOR SEND OPERATIONS

For send operations, the only use of status is for MPI_Test_cancelled 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.

ERRORS

If an error occurs in an MPI function, the current MPI error handler is called to handle it. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Errhandler_set ; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned (in C and Fortran; this error handler is less useful in with the C++ MPI bindings. The predefined error handler MPI::ERRORS_THROW_EXCEPTIONS should be used in C++ if the error value needs to be recovered). Note that MPI does not guarantee that an MPI program can continue past an error.

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. The C++ bindings for MPI do not return error values; instead, error values are communicated by throwing exceptions of type MPI::Exception (but not by default). Exceptions are only thrown if the error value is not MPI::SUCCESS .

Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return upon an error, there will be no way to recover what the actual error value was.
MPI_SUCCESS
    - No error; MPI routine completed successfully.
MPI_ERR_REQUEST
    - Invalid MPI_Request ; either null or, MPI_REQUEST_NULL , in the case of a MPI_Start or MPI_Startall , not a persistent request.
MPI_ERR_COUNT
    - Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
MPI_ERR_ARG
    - Invalid argument. Some argument is invalid and is not identified by a specific error class. This is typically a NULL pointer or other such error.

MPI_ERR_IN_STATUS
    - The actual error value is in the MPI_Status argument. Note that if this error occurs and MPI_STATUS_IGNORE or MPI_STATUSES_IGNORE was used as the status argument, the actual error will be lost. 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)? LAM/MPI 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 .

MORE INFORMATION

For more information, please see the official MPI Forum web site, which contains the text of both the MPI-1 and MPI-2 standards. These documents contain detailed information about each MPI function (most of which is not duplicated in these man pages).

http://www.mpi-forum.org/

ACKNOWLEDGEMENTS

The LAM Team would like the thank the MPICH Team for the handy program to generate man pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial formatting, and some initial text for most of the MPI-1 man pages.

LOCATION
waitsome.c