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 MPI_Win_lock_all