MPI_Win_lock(3)                    Open MPI                    MPI_Win_lock(3)



NAME
       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
       INCLUDE 'mpif.h'
       MPI_WIN_LOCK(LOCK_TYPE, RANK, ASSERT, WIN, IERROR)
            INTEGER LOCK_TYPE, RANK, ASSERT, WIN, IERROR


C++ Syntax
       #include <mpi.h>
       void MPI::Win::Lock(int lock_type, int rank, int assert) const


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.


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 MPI_Win_lock
       call, failing to notice that the peer MPI job has terminated.


ERRORS
       Almost all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last argument. C++
       functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before the error value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed with
       MPI_Comm_set_errhandler; 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.


See also
       MPI_Win_unlock




1.4.1                            Jan 14, 2010                  MPI_Win_lock(3)
