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MPI_Win_lock(3)			      MPI		       MPI_Win_lock(3)

NAME
       MPI_Win_lock -  Begin an	RMA access epoch at the	target process

SYNOPSIS
       int MPI_Win_lock(int lock_type, int rank, int assert, MPI_Win win)

INPUT PARAMETERS
       lock_type
	      -	either MPI_LOCK_EXCLUSIVE or MPI_LOCK_SHARED (state)
       rank   -	rank of	locked window (non-negative integer)
       assert -	program	assertion (integer)
       win    -	window object (handle)

NOTES
       The  name  of  this routine is misleading.  In particular, this routine
       need not	block, except when the target process is the calling process.

       Implementations may restrict the	use of RMA communication that is  syn-
       chronized by lock calls to windows in memory allocated by MPI_Alloc_mem
       .  Locks	can be used portably only in such memory.

       The  assert  argument  is  used	to indicate special conditions for the
       fence that an implementation may	use to optimize	the MPI_Win_lock oper-
       ation.  The value zero is always	correct.  Other	assertion  values  may
       be or'ed	together.  Assertions that are valid for MPI_Win_lock are:

       MPI_MODE_NOCHECK
	      -	no other process holds,	or will	attempt	to acquire a conflict-
	      ing lock,	while the caller holds the window lock.	This is	useful
	      when mutual exclusion is achieved	by other means,	but the	coher-
	      ence  operations	that  may  be  attached	to the lock and	unlock
	      calls are	still required.

THREAD AND INTERRUPT SAFETY
       This routine is thread-safe.  This  means  that	this  routine  may  be
       safely  used by multiple	threads	without	the need for any user-provided
       thread locks.  However, the routine is not interrupt safe.   Typically,
       this  is	due to the use of memory allocation routines such as malloc or
       other non-MPICH runtime routines	that  are  themselves  not  interrupt-
       safe.

NOTES FOR FORTRAN
       All  MPI	routines in Fortran (except for	MPI_WTIME and MPI_WTICK	) have
       an additional argument ierr at the end of the argument list.   ierr  is
       an  integer and has the same meaning as the return value	of the routine
       in C.  In Fortran, MPI routines are subroutines,	and are	 invoked  with
       the call	statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm )	are of type INTEGER in
       Fortran.

ERRORS
       All  MPI	 routines  (except  MPI_Wtime  and MPI_Wtick ) return an error
       value; C	routines as the	value of the function and Fortran routines  in
       the last	argument.  Before the value is returned, the current MPI error
       handler	is called.  By default,	this error handler aborts the MPI job.
       The error handler may be	changed	with MPI_Comm_set_errhandler (for com-
       municators), MPI_File_set_errhandler (for files),  and  MPI_Win_set_er-
       rhandler	 (for  RMA windows).  The MPI-1	routine	MPI_Errhandler_set may
       be used but its	use  is	 deprecated.   The  predefined	error  handler
       MPI_ERRORS_RETURN  may  be  used	 to cause error	values to be returned.
       Note that MPI does not guarantee	that an	MPI program can	continue  past
       an  error;  however, MPI	implementations	will attempt to	continue when-
       ever possible.

       MPI_SUCCESS
	      -	No error; MPI routine completed	successfully.
       MPI_ERR_RANK
	      -	Invalid	source or destination rank.   Ranks  must  be  between
	      zero  and	the size of the	communicator minus one;	ranks in a re-
	      ceive ( MPI_Recv , MPI_Irecv , MPI_Sendrecv , etc.) may also  be
	      MPI_ANY_SOURCE .

       MPI_ERR_WIN
	      -	Invalid	MPI window object
       MPI_ERR_OTHER
	      -	 Other	error;	use  MPI_Error_string  to get more information
	      about this error code.

				   2/3/2025		       MPI_Win_lock(3)

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