MPI_FETCH_AND_OP(3)				     Open MPI				       MPI_FETCH_AND_OP(3)

MPI_Fetch_and_op  — Combines the contents of the origin buffer with that of a target buffer and returns the target
buffer value.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Fetch_and_op(const void *origin_addr, void *result_addr,
	       MPI_Datatype datatype, int target_rank, MPI_Aint target_disp,
	       MPI_Op op, MPI_Win win)

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

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Fetch_and_op(origin_addr, result_addr, datatype, target_rank,
		       target_disp, op, win, ierror)
	       TYPE(*), DIMENSION(..), INTENT(IN) :: origin_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_Op), INTENET(IN) :: op
	       TYPE(MPI_Win), INTENT(IN) :: win
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS
       • origin_addr: Initial address of 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).

       • op: Reduce operation (handle).

       • win: Window object (handle).

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

DESCRIPTION
       Accumulate one element of type datatype from the origin	buffer	(origin_addr)  to  the	buffer	at  offset
       target_disp,  in	 the  target window specified by target_rank and win, using the operation op and return in
       the result buffer result_addr the contents of the target buffer before the accumulation.

       The origin and result buffers (origin_addr and  result_addr)  must  be  disjoint.  Any  of  the	predefined
       operations  for	MPI_Rreduce,  as  well	as  MPI_NO_OP or MPI_REPLACE, can be specified as op; user-defined
       functions cannot be used. The datatype argument must be a predefined datatype. The  operation  is  executed
       atomically.

       A new predefined operation, MPI_REPLACE, is defined. It corresponds to the associative function f(a, b) =b;
       that is, the current value in the target memory is replaced by the value supplied by the origin.

       A  new predefined operation, MPI_NO_OP, is defined. It corresponds to the assiciative function f(a, b) = a;
       that is the current value in the target memory is returned in the  result  buffer  at  the  origin  and	no
       operation is performed on the target buffer.

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_Fetch_and_op 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>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#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 <#
       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>/MPI_Comm_spawn_multiple	<#
       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 <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#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	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

       See also:

	  • MPI_Get_accumulate <#mpi-get-accumulate>

	  • MPI_Reduce <#mpi-reduce>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				       MPI_FETCH_AND_OP(3)
