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 synchronized 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 operation.  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 conflicting lock, while  the  caller  holds
              the  window  lock.  This  is  useful  when  mutual  exclusion  is achieved by other means, but the
              coherence 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   communicators),   MPI_File_set_errhandler   (for   files),   and
       MPI_Win_set_errhandler (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 whenever 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  receive  (  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.

                                                    2/9/2024                                     MPI_Win_lock(3)