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.

                                            2/22/2022                             MPI_Win_lock(3)