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MPI_Win_lock.3.rst

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MPI_Win_lock

:ref:`MPI_Win_lock` - Starts an RMA access epoch locking access to a particular rank.

SYNTAX

C Syntax

#include <mpi.h>

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

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_WIN_LOCK(LOCK_TYPE, RANK, ASSERT, WIN, IERROR)
     INTEGER LOCK_TYPE, RANK, ASSERT, WIN, IERROR

Fortran 2008 Syntax

USE mpi_f08
MPI_Win_lock(lock_type, rank, assert, win, ierror)
     INTEGER, INTENT(IN) :: lock_type, rank, assert
     TYPE(MPI_Win), INTENT(IN) :: win
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

  • lock_type: Either MPI_LOCK_EXCLUSIVE or MPI_LOCK_SHARED (state).
  • rank: Rank of locked window (nonnegative integer).
  • assert: Program assertion (integer).
  • win: Window object (handle).

OUTPUT PARAMETER

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

DESCRIPTION

Starts an RMA access epoch. Locks ensure that only the windows created by specific processes can be accessed by those processes (and by no other processes) during that epoch.

Locks are used to protect accesses to the locked target window effected by RMA calls issued between the lock and unlock call, and to protect local load/store accesses to a locked local window executed between the lock and unlock call. Accesses that are protected by an exclusive lock will not be concurrent at the window site with other accesses to the same window that are lock protected. Accesses that are protected by a shared lock will not be concurrent at the window site with accesses protected by an exclusive lock to the same window.

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
No other processes will hold or attempt to acquire a conflicting lock while the caller holds the window lock.

NOTES

In a client/server environment in which clients connect to a server and create windows that span both the client and the server, if a client or server that has obtained a lock on such a window and then terminates abnormally, the server or other clients may hang in a :ref:`MPI_Win_lock` call, failing to notice that the peer MPI job has terminated.

ERRORS

.. seealso::
   * :ref:`MPI_Win_unlock`
   * :ref:`MPI_Win_lock_all`