Currently, when a signal arrives in the main thread, the signal dispatcher is
retrieved and called from the main thread, the dispatcher uses a proxy object
that in turn sends an RPC to the entry point. This becomes a problem when the
entry point destroys the dispatcher object, before the dispatch function has
been called by the main thread. Therefore, the main thread should simply send an
RPC to the entry point upon signal arrival and the dispatching should be handled
solely by the entry point.
Issue #1738
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082
