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       MPI_Waitall -  Waits for all given MPI Requests to complete


       int MPI_Waitall(int count, MPI_Request array_of_requests[], MPI_Status array_of_statuses[])


       count  - list length (integer)
              - array of request handles (array of handles)


              - array of status objects (array of Statuses).  May be MPI_STATUSES_IGNORE .


       If one or more of the requests completes with an error, MPI_ERR_IN_STATUS is returned.  An
       error value will be present is elements of array_of_status associated with  the  requests.
       Likewise,  the  MPI_ERROR  field in the status elements associated with requests that have
       successfully completed will be MPI_SUCCESS  .   Finally,  those  requests  that  have  not
       completed will have a value of MPI_ERR_PENDING .

       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.


       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


       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  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.


       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.

              - No error; MPI routine completed successfully.
              - Invalid MPI_Request .  Either null or, in the case of a MPI_Start or MPI_Startall
              , not a persistent request.
              -  Invalid  argument.  Some argument is invalid and is not identified by a specific
              error class (e.g., MPI_ERR_RANK ).
              - 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 .

                                            11/21/2018                             MPI_Waitall(3)