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 .

                                                   11/12/2019                                    MPI_Waitsome(3)