MPI_WIN_START(3)				     Open MPI					  MPI_WIN_START(3)

MPI_Win_start — Starts an RMA access epoch for win

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Win_start(MPI_Group group, int assert, MPI_Win win)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_WIN_START(GROUP, ASSERT, WIN, IERROR)
	       INTEGER GROUP, ASSERT, WIN, IERROR

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Win_start(group, assert, win, ierror)
	       TYPE(MPI_Group), INTENT(IN) :: group
	       INTEGER, INTENT(IN) :: assert
	       TYPE(MPI_Win), INTENT(IN) :: win
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS
       • group: The group of target processes (handle).

       • assert: Program assertion (integer).

       • win: Window object (handle).

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

DESCRIPTION
       MPI_Win_start  is  a  one-sided	MPI communication synchronization call that starts an RMA access epoch for
       win. RMA calls issued on win during this epoch must access only windows at processes in group. Each process
       in group must issue a matching call to MPI_Win_post <#mpi-win-post>.  MPI_Win_start  is	allowed	 to  block
       until the corresponding MPI_Win_post <#mpi-win-post> calls have been executed, but is not required to.

       The  assert  argument is used to provide assertions on the context of the call that may be used for various
       optimizations. (See Section 6.4.4 of the MPI-2 Standard.) A value of  assert  =	0  is  always  valid.  The
       following assertion value is supported:

       MPI_MODE_NOCHECK
	      When  this value is passed in to this call, the library assumes that the post call on the target has
	      been called and it is not necessary for the library to check to see if such a call has been made.

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_Win_post <#mpi-win-post>

	  • MPI_Win_complete <#mpi-win-complete>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					  MPI_WIN_START(3)
