The in-image atomicity of determining whether a signal was actually
consumed or not during process suspension/termination is awkward. Its
seems hard to *really* know for sure it right (but I haven't looked in
depth into Denis' latest proposals.)
I realize that my proposals was wrong because it is based on extra message send which can be interrupted. So I think about different solution.
Current solution which silently skip ensure block not suitable for case of ReadWriteLock where there are two semaphores inside same critical method