--- name: "MPI_Waitsome" section: "3" platform: "linux" package: "openmpi" version: "5.0.11-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/MPI_Waitsome" --- # MPI\_Waitsome(3) *MPI\_Waitsome* — Waits for some given communications to complete. ## SYNTAX ### C Syntax ``` #include 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 2003-2026, The Open MPI Community