MPI One Sided: Exclusive Lock with MPI_Win_lock_all

Question

The MPI-3 Standard states that MPI_Win_lock(...) with lock type MPI_LOCK_SHARED must be a blocking (exclusive) lock if and only if the origin and target process are the same. MPI_Win_lock_all is the locking of all processes in the window with lock type MPI_LOCK_SHARED.

Does this imply that MPI_Win_lock_all creates also an exclusive lock from the origin to the origin itself?

Answer 1

No. MPI_Win_lock_all induces a shared lock at all processes associated with the window (technically, in the group associated with the window).

In any case, a shared lock and an exclusive lock are different. Please do not conflate the possibility that shared lock acquisition will block on some remote state with an exclusive lock.