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MPI_Waitsome(3) MPI MPI_Waitsome(3)
MPI_Waitsome - Waits for some given MPI Requests to complete
int MPI_Waitsome(int incount, MPI_Request array_of_requests,
int *outcount, int array_of_indices,
- length of array_of_requests (integer)
- array of requests (array of handles)
- number of completed requests (integer)
- array of indices of operations that completed (array of
- array of status objects for operations that completed (array
of Status). May be MPI_STATUSES_IGNORE .
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 .
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.
MPI_Waitsome provides an interface much like the Unix select or poll
calls and, in a high qualilty implementation, indicates all of the
requests that have completed when MPI_Waitsome is called. However,
MPI_Waitsome only guarantees that at least one request has completed;
there is no guarantee that all completed requests will be returned, or
that the entries in array_of_indices will be in increasing order. Also,
requests that are completed while MPI_Waitsome is executing may or may
not be returned, depending on the timing of the completion of the
NOTES ON THE MPI_STATUS ARGUMENT
The MPI_ERROR field of the status return is only set if the return from
the MPI routine is MPI_ERR_IN_STATUS . That error class is only
returned by the routines that take an array of status arguments (
MPI_Testall , MPI_Testsome , MPI_Waitall , and MPI_Waitsome ). In all
other cases, the value of the MPI_ERROR field in the status is
unchanged. See section 3.2.5 in the MPI-1.1 specification for the
For send operations, the only use of status is for MPI_Test_cancelled
or in the case that there is an error in one of the four routines that
may return the error class MPI_ERR_IN_STATUS , in which case the
MPI_ERROR field of status will be set. In that case, the value will be
set to MPI_SUCCESS for any send or receive operation that completed
successfully, or MPI_ERR_PENDING for any operation which has neither
failed nor completed.
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-
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
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.
- 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 ).
- 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