--- name: "MPIX_Comm_ack_failed.openmpi" section: "3" platform: "linux" package: "openmpi-doc" version: "5.0.7-1" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/MPIX_Comm_ack_failed.openmpi" --- # MPIX\_Comm\_ack\_failed.openmpi(3) *MPIX\_Comm\_get\_failed* - acknowledge failed processes in a communicator. This is part of the User Level Fault Mitigation *ULFM extension*. ## SYNTAX ### C Syntax ``` #include #include 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