Provided by: openmpi-doc_5.0.7-1_all 
SYNTAX
C Syntax
#include <mpi.h>
int MPI_Waitsome(int incount, MPI_Request array_of_requests[],
int *outcount, int array_of_indices[],
MPI_Status array_of_statuses[])
Fortran Syntax
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_WAITSOME(INCOUNT, ARRAY_OF_REQUESTS, OUTCOUNT,
ARRAY_OF_INDICES, ARRAY_OF_STATUSES, IERROR)
INTEGER INCOUNT, ARRAY_OF_REQUESTS(*), OUTCOUNT
INTEGER ARRAY_OF_INDICES(*)
INTEGER ARRAY_OF_STATUSES(MPI_STATUS_SIZE*)
INTEGER IERROR
Fortran 2008 Syntax
USE mpi_f08
MPI_Waitsome(incount, array_of_requests, outcount, array_of_indices,
array_of_statuses, ierror)
INTEGER, INTENT(IN) :: incount
TYPE(MPI_Request), INTENT(INOUT) :: array_of_requests(incount)
INTEGER, INTENT(OUT) :: outcount, array_of_indices(*)
TYPE(MPI_Status) :: array_of_statuses(*)
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
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
Waits until at least one of the operations associated with active handles in the list have completed.
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 the list contains no active handles, then the call returns immediately with outcount = MPI_UNDEFINED.
When one or more of the communications completed by MPI_Waitsome fails, then it is desirable to return
specific information on each communication. The arguments outcount, array_of_indices, and
array_of_statuses will be adjusted to indicate completion of all communications that have succeeded or
failed. The call will return the error code MPI_ERR_IN_STATUS and the error field of each status returned
will be set to indicate success or to indicate the specific error that occurred. The call will return
MPI_SUCCESS if no request resulted in an error, and will return another error code if it failed for other
reasons (such as invalid arguments). In such cases, it will not update the error fields of the statuses.
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.
Example: Same code as the example in the MPI_Waitany man page, but using MPI_Waitsome.
CALL MPI_COMM_SIZE(comm, size, ierr)
CALL MPI_COMM_RANK(comm, rank, ierr)
IF(rank > 0) THEN ! client code
DO
CALL MPI_ISEND(a, n, MPI_REAL, 0, tag, comm, request, ierr)
CALL MPI_WAIT(request, status, ierr)
END DO
ELSE ! rank=0: server code
DO i=1, size-1
CALL MPI_IRECV(a(1,i), n, MPI_REAL, i, tag, &
comm, requests(i), ierr)
END DO
DO
CALL MPI_WAITSOME(size, request_list, numdone, &
indices, statuses, ierr)
DO i=1, numdone
CALL DO_SERVICE(a(1, indices(i)))
CALL MPI_IRECV(a(1, indices(i)), n, MPI_REAL, i, tag, &
comm, requests(indices(i)), ierr)
END DO
END DO
END IF
NOTES
The array of indices are in the range 0 to incount-1 for C and in the range 1 to incount for Fortran.
ERRORS
Almost all MPI routines return an error value; C routines as the return result of the function and
Fortran routines in the last argument.
Before the error value is returned, the current MPI error handler associated with the communication
object (e.g., communicator, window, file) is called. If no communication object is associated with the
MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error
handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after
MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler.
The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/‐
MPI_Comm_spawn_multiple. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all
other MPI functions.
Open MPI includes three predefined error handlers that can be used:
• MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.
• MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a
window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in
the corresponding window or file. If called on a session, aborts only the local process.
• MPI_ERRORS_RETURN Returns an error code to the application.
MPI applications can also implement their own error handlers by calling:
• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler
Note that MPI does not guarantee that an MPI program can continue past an error.
See the MPI man page for a full list of MPI error codes.
See the Error Handling section of the MPI-3.1 standard for more information.
For each invocation of MPI_Waitsome, if one or more requests generate an MPI error, only the first MPI
request that caused an error will be passed to its corresponding error handler. No other error handlers
will be invoked (even if multiple requests generated errors). However, all requests that generate an
error will have a relevant error code set in the corresponding status.MPI_ERROR field (unless
MPI_STATUSES_IGNORE was used).
If the invoked error handler allows MPI_Waitsome to return to the caller, the value MPI_ERR_IN_STATUS
will be returned in the C and Fortran bindings.
SEE ALSO:
• MPI_Comm_set_errhandler
• MPI_File_set_errhandler
• MPI_Test
• MPI_Testall
• MPI_Testany
• MPI_Testsome
• MPI_Wait
• MPI_Waitall
• MPI_Waitany
• MPI_Win_set_errhandler
COPYRIGHT
2003-2025, The Open MPI Community
Feb 17, 2025 MPI_WAITSOME(3)