Re: Windows buildfarm members vs. new async-notify isolation test

I wrote:
> So, just idly looking at the code in src/backend/port/win32/signal.c
> and src/port/kill.c, I have to wonder why we have this baroque-looking
> design of using *two* signal management threads.  And, if I'm
> reading it right, we create an entire new pipe object and an entire
> new instance of the second thread for each incoming signal.  Plus, the
> signal senders use CallNamedPipe (hence, underneath, TransactNamedPipe)
> which means they in effect wait for the recipient's signal-handling
> thread to ack receipt of the signal.  Maybe there's a good reason for
> all this but it sure seems like a lot of wasted cycles from here.

Here's a possible patch (untested by me) to get rid of the second thread
and the new-pipe-for-every-request behavior.  I believe that the existing
logic may be based on Microsoft's "Multithreaded Pipe Server" example [1]
or something similar, but that's based on an assumption that servicing
a client request may take a substantial amount of time and it's worth
handling requests concurrently.  Neither point applies in this context.

Doing it like this seems attractive to me because it gets rid of two
different failure modes: inability to create a new thread and inability
to create a new pipe handle.  Now on the other hand, it means that
inability to complete the read/write transaction with a client right
away will delay processing of other signals.  But we know that the
client is engaged in a CallNamedPipe operation, so how realistic is
that concern?

This is to be applied on top of the other patch I just sent.

			regards, tom lane

[1] https://docs.microsoft.com/en-us/windows/win32/ipc/multithreaded-pipe-server