SYNTAX

   C Syntax
          #include <mpi.h>
          #include <mpi-ext.h>

          int MPIX_Comm_ack_failed(MPI_Comm comm, int num_to_ack, int *num_acked)

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

          MPIX_COMM_ACK_FAILED(COMM, NUM_TO_ACK, NUM_ACKED, IERROR)
               INTEGER COMM, NUM_TO_ACK, NUM_ACKED, IERROR

   Fortran 2008 Syntax
          USE mpi_f08
          USE mpi_ext_f08

          MPIX_Comm_ack_failed(comm, num_to_ack, num_acked, ierror)
               TYPE(MPI_Comm), INTENT(IN) :: comm
               INTEGER, INTENT(IN) :: num_to_ack
               INTEGER, INTENT(OUT) :: num_acked
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

       • comm: Communicator (handle).

       • num_to_ack: maximum number of process failures to acknowledge in comm (integer)

OUTPUT PARAMETERS

       • num_acked: number of acknowledged failures in comm (integer).

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

DESCRIPTION

       his local operation gives the users a way to acknowledge locally notified failures on comm. The operation
       acknowledges  the  first  num_to_ack  process  failures  on comm, that is, it acknowledges the failure of
       members with a rank lower than num_to_ack in the group that would be produced by  a  concurrent  call  to
       MPIX_Comm_get_failed on the same comm.

       The  operation also sets the value of num_acked to the current number of acknowledged process failures in
       comm, that is, a process failure has been acknowledged on comm if and only if the rank of the process  is
       lower  than num_acked in the group that would be produced by a subsequent call to MPIX_Comm_get_failed on
       the same comm.

       num_acked can be larger than num_to_ack when process failures have been acknowledged in a prior  call  to
       MPIX_Comm_ack_failed.

EFFECT OF ACKNOWLEDGING FAILURES

       After  an MPI process failure is acknowledged on comm, unmatched MPI_ANY_SOURCE receive operations on the
       same comm that would have raised an error of class MPIX_ERR_PROC_FAILED_PENDING proceed  without  further
       raising errors due to this acknowledged failure.

       Also,  MPIX_Comm_agree  on the same comm will not raise an error of class MPI_ERR_PROC_FAILED due to this
       acknowledged failure.

USAGE PATTERNS

       One may query, without side effect, for the number of currently  aknowledged  process  failures  comm  by
       supplying 0 in num_to_ack.

       Conversely, one may unconditionally acknowledge all currently known process failures in comm by supplying
       the size of the group of comm in num_to_ack.

       Note  that  the number of acknowledged processes, as returned in num_acked, can be smaller or larger than
       the value supplied in num_to_ack; It is however never larger than the size of the  group  returned  by  a
       subsequent call to MPIX_Comm_get_failed.

EFFECT ON COLLECTIVE OPERATIONS

       Calling  MPIX_Comm_ack_failed  on  a  communicator  with failed MPI processes has no effect on collective
       operations (except for MPIX_Comm_agree).  If a collective operation would  raise  an  error  due  to  the
       communicator  containing  a  failed process it will continue to raise an error even after the failure has
       been acknowledged. In order to use collective operations between MPI processes  of  a  communicator  that
       contains   failed   MPI   processes,   users   should   create  a  new  communicator  (e.g.,  by  calling
       MPIX_Comm_shrink).

WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR

       When the communicator is an inter-communicator, the failures of members in both the local and the  remote
       groups of comm are acknowledged.

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.

       SEE ALSO:

          • MPIX_Comm_get_failed

          • MPIX_Comm_agree

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                           MPIX_COMM_ACK_FAILED(3)