plucky (3) MPI_Grequest_start.openmpi.3.gz

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SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_Grequest_start(MPI_Grequest_query_function *query_fn,
              MPI_Grequest_free_function *free_fn,
              MPI_Grequest_cancel_function *cancel_fn, void *extra_state,
              MPI_Request *request)

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'

          MPI_GREQUEST_START(QUERY_FN, FREE_FN, CANCEL_FN, EXTRA_STATE,
              REQUEST, IERROR)
              INTEGER REQUEST, IERROR
              EXTERNAL QUERY_FN, FREE_FN, CANCEL_FN
                INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE

   Fortran 2008 Syntax
          USE mpi_f08

          MPI_Grequest_start(query_fn, free_fn, cancel_fn, extra_state, request,
                  ierror)
              PROCEDURE(MPI_Grequest_query_function) :: query_fn
              PROCEDURE(MPI_Grequest_free_function) :: free_fn
              PROCEDURE(MPI_Grequest_cancel_function) :: cancel_fn
              INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: extra_state
              TYPE(MPI_Request), INTENT(OUT) :: request
              INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

query_fn (Callback function invoked when request status is)
                queried (function).

       •

         free_fn (Callback function invoked when request is freed)
                (function).

       •

         cancel_fn (Callback function invoked when request is canceled)
                (function).

       • extra_state : Extra state.

OUTPUT PARAMETERS

request : Generalized request (handle).

       • ierror : Fortran only: Error status (integer).

DESCRIPTION

       MPI_Grequest_start starts a generalized request and returns a handle to it in request.

       The  syntax and meaning of the callback functions are listed below. All callback functions are passed the
       extra_state argument that was associated with the request by the starting call  MPI_Grequest_start.  This
       can be used to maintain user-defined state for the request. In C, the query function is

          typedef int MPI_Grequest_query_function(void *extra_state,
              MPI_Status *status);

       In Fortran, it is

          SUBROUTINE GREQUEST_QUERY_FUNCTION(EXTRA_STATE, STATUS, IERROR)
              INTEGER STATUS(MPI_STATUS_SIZE), IERROR
              INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE

       The query_fn function computes the status that should be returned for the generalized request. The status
       also includes information about  successful/unsuccessful  cancellation  of  the  request  (result  to  be
       returned by MPI_Test_cancelled).

       The query_fn function is invoked by the MPI_{Wait|Test}{any|some|all} call that completed the generalized
       request  associated  with  this  callback.  The  callback  function  is  also   invoked   by   calls   to
       MPI_Request_get_status  if  the  request is complete when the call occurs. In both cases, the callback is
       passed a reference to the corresponding status variable passed by the user to the MPI call. If  the  user
       provided  MPI_STATUS_IGNORE or MPI_STATUSES_IGNORE to the MPI function that causes query_fn to be called,
       then MPI will pass a valid status object to query_fn, and this status will be ignored upon return of  the
       callback  function.  Note  that  query_fn  is  invoked  only after MPI_Grequest_complete is called on the
       request; it may be invoked several times for the same generalized request.  Note  also  that  a  call  to
       MPI_{Wait|Test}{some|all}  may  cause  multiple  invocations of query_fn callback functions, one for each
       generalized request that is completed by the MPI call. The order of these invocations is not specified by
       MPI.

       In C, the free function is

          typedef int MPI_Grequest_free_function(void *extra_state);

       And in Fortran, it is

          SUBROUTINE GREQUEST_FREE_FUNCTION(EXTRA_STATE, IERROR)
              INTEGER IERROR
              INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE

       The  free_fn  callback  function  is  invoked  to  clean up user-allocated resources when the generalized
       request is freed.

       The free_fn function is invoked by the MPI_{Wait|Test}{any|some|all} call that completed the  generalized
       request  associated  with  this  callback.  free_fn  is  invoked  after the call to query_fn for the same
       request. However, if the MPI call completed multiple generalized requests, the  order  in  which  free_fn
       callback functions are invoked is not specified by MPI.

       The   free_fn  callback  is  also  invoked  for  generalized  requests  that  are  freed  by  a  call  to
       MPI_Request_free (no call to MPI_{Wait|Test}{any|some|all} will occur for such a request). In this  case,
       the  callback function will be called either in the MPI call MPI_Request_free(request) or in the MPI call
       MPI_Grequest_complete(request), whichever happens last. In other words, in this case the  actual  freeing
       code  is  executed  as soon as both calls (MPI_Request_free and MPI_Grequest_complete) have occurred. The
       request is not deallocated until after free_fn completes. Note that free_fn will be invoked only once per
       request by a correct program.

       In C, the cancel function is

          typedef int MPI_Grequest_cancel_function(void *extra_state, int complete);

       In Fortran, the cancel function is

          SUBROUTINE GREQUEST_CANCEL_FUNCTION(EXTRA_STATE, COMPLETE, IERROR)
               INTEGER IERROR
               INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE
               LOGICAL COMPLETE

       The  cancel_fn  function  is  invoked to start the cancellation of a generalized request. It is called by
       MPI_Request_cancel(request).  MPI passes to the callback function complete=true if  MPI_Grequest_complete
       has already been called on the request, and complete=false otherwise.

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_errhandlerMPI_File_create_errhandler then MPI_File_set_errhandlerMPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_initMPI_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.

       All callback functions return an error code. The code is passed back and dealt with  as  appropriate  for
       the  error  code  by the MPI function that invoked the callback function. For example, if error codes are
       returned, then the error code returned by the callback function will be returned by the MPI function that
       invoked  the  callback  function. In the case of a MPI_{Wait|Test}any call that invokes both query_fn and
       free_fn, the MPI call will return the error code returned by the last callback, namely free_fn. If one or
       more of the request``s in a call to ``MPI_{Wait|Test}{some|all} has failed, then the MPI call will return
       MPI_ERR_IN_STATUS. In such a case, if the MPI call was passed an array of statuses, then MPI will  return
       in each of the statuses that correspond to a completed generalized request the error code returned by the
       corresponding invocation of its free_fn callback function.  However,  if  the  MPI  function  was  passed
       MPI_STATUSES_IGNORE, then the individual error codes returned by each callback function will be lost.

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                             MPI_GREQUEST_START(3)