int MPI_Waitsome(int incount, MPI_Request array_of_requests, int *outcount, int array_of_indices, MPI_Status *array_of_statuses)
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.
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.
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.
All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.
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 guarantee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.