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MPIX_Comm_ack_failed.3.rst

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MPIX_Comm_ack_failed

MPIX_Comm_get_failed - acknowledge failed processes in a communicator.

This is part of the User Level Fault Mitigation ULFM extension <ulfm-label>.

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

* MPIX_Comm_get_failed * MPIX_Comm_agree