Provided by: mpich-doc_3.3~a2-4_all 
NAME
MPI_Waitsome - Waits for some given MPI Requests to complete
SYNOPSIS
int MPI_Waitsome(int incount, MPI_Request array_of_requests[],
int *outcount, int array_of_indices[],
MPI_Status array_of_statuses[])
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). May be
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 .
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 message.
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 exact text.
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-safe.
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
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.
MPI_SUCCESS
- No error; MPI routine completed successfully.
MPI_ERR_REQUEST
- Invalid MPI_Request . Either null or, in the case of a MPI_Start or MPI_Startall
, not a persistent request.
MPI_ERR_ARG
- Invalid argument. Some argument is invalid and is not identified by a specific
error class (e.g., MPI_ERR_RANK ).
MPI_ERR_IN_STATUS
- 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 MPI_ERR_PENDING .
11/12/2016 MPI_Waitsome(3)