SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_Compare_and_swap(const void *origin_addr, const void *compare_addr,
               void *result_addr, MPI_Datatype datatype, int target_rank,
               MPI_Aint target_disp, MPI_Win win)

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_COMPARE_AND_SWAP(ORIGIN_ADDR, COMPARE_ADDR, RESULT_ADDR, DATATYPE, TARGET_RANK,
               TARGET_DISP, WIN, IERROR)
               <type> ORIGIN_ADDR, COMPARE_ADDR, RESULT_ADDR(*)
               INTEGER(KIND=MPI_ADDRESS_KIND) TARGET_DISP
               INTEGER DATATYPE, TARGET_RANK, WIN, IERROR

   Fortran 2008 Syntax
          USE mpi_f08
          MPI_Compare_and_swap(origin_addr, compare_addr, result_addr, datatype,
                       target_rank, target_disp, win, ierror)
               TYPE(*), DIMENSION(..), INTENT(IN) :: origin_addr, compare_addr
               TYPE(*), DIMENSION(..) :: result_addr
               TYPE(MPI_Datatype), INTENT(IN) :: datatype
               INTEGER, INTENT(IN) :: target_rank
               INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: target_disp
               TYPE(MPI_Win), INTENT(IN) :: win
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

       • origin_addr: Initial address of buffer (choice).

       • compare_addr: Initial address of compare buffer (choice).

       • result_addr: Initial address of result buffer (choice).

       • datatype: Data type of the entry in origin, result, and target buffers (handle).

       • target_rank: Rank of target (nonnegative integer).

       • target_disp: Displacement from start of window to beginning of target buffer (nonnegative integer).

       • win: Window object (handle).

OUTPUT PARAMETER

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

DESCRIPTION

       This function compares one element of type datatype in the compare buffer compare_addr with the buffer at
       offset  target_disp  in  the target window specified by target_rank and win and replaces the value at the
       target with the value in the origin buffer origin_addr if the compare buffer and the  target  buffer  are
       identical. The original value at the target is returned in the buffer result_addr. The parameter datatype
       must  belong  to  one  of  the  following categories of predefined datatypes: C integer, Fortran integer,
       Logical, Multi-language types, or Byte as specified in MPI-3 section 5.9.2 on page 176.

       The origin and result buffers (origin_addr and result_addr) must be disjoint.

NOTES

       It is the user’s responsibility to guarantee that,  when  using  the  accumulate  functions,  the  target
       displacement argument is such that accesses to the window are properly aligned according to the data type
       arguments in the call to the MPI_Compare_and_swap function.

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.

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                           MPI_COMPARE_AND_SWAP(3)