From: Thomas Sondergaard <thomas@...>
Date: 2003-09-18T09:32:21+09:00
Subject: Thread safety: Serializing access to ruby interpreter- again

I recently asked about this and got answers, but here I go again:

How can I efficiently serialize access to the ruby interpreter. I have to
make sure all access to the ruby interpreter happens on a particular thread
(not a ruby thread, mind you), so when a different thread attempts to access
the ruby interpreter I need it to have it post the job to a queue and then
wait for a ruby worker thread on the ruby-thread (:-)) to execute whatever
it needs done. Btw, in this mail I use the term ruby-thread, with a dash in
the middle, as a reference to the heavy-weight thread in which the ruby
interpreter executes.

The thing is that if I have a ruby thread on the ruby-thread block on a
heavyweight thread lock the entire ruby-thread is blocked. This is
demonstrated by this bit below (which requires my dotnet module to work). It
simply starts a thread that writes to the console continuously and then the
main thread waits for a signal on anObject. However that wait() call blocks
the entire ruby-thread not just the "green" ruby main thread, so I never get
to see a steady stream of hello worlds, and that is what ruins my day.

require 'dotnet'

t = Thread.new { while true; sleep 0.1; puts "hello world"; end }

anObject = System::EventArgs.new

System::Threading::Monitor.enter(anObject)
System::Threading::Monitor.wait(anObject) # This blocks the entire
ruby-thread
System::Threading::Monitor.exit(anObject)

t.join


So if I am not allowed to touch the ruby interpreter from other threads than
the ruby-thread how can I wake up a sleeping worker thread when there is
something for it to do?

Is there a heavyweight-thread-safe way to wake up a ruby thread? Shouldn't
there be?

- Thomas