Run trap handler in an independent thread called "Signal thread"
How about to make an "Signal thread" to run trap handler?
Now, all of thread synchronization methods are not permitted because there is a possibility of deadlock between trap handler and main thraed.
m = Mutex.new
... # recv SIGINT, and invoke trap handler
In this case, trap handler (a block passed to trap method) is run on the main thread.
Make a signal handler independent from main thread. If main thread and trap handler run in different threads, there are no such problem.
Don't create signal handler at first. But the first time we need a signal handler, signal handler is created by main thread.
See timing chart (PDF) I attached.
- Signal thread is independent on main thread, this means that you can use thread synchronization between trap handler and main thread. In other words, you can run any program in trap handler.
- Simplify a path from sighandler to trap invocation thread (after creation of a signal thread)
- Doesn’t need a difficult implementation (modify is limited).
- There is a small compatibility issue because “Thread.current” on a trap handler is not a main thread.
== Other Discussion:
- Create signal thread at first like timer thread is high cost. Without `trap’, we don’t need a signal thread any more.
- In signal handler and timer thread, we can’t make a signal thread because creating “Ruby thread” (== signal thread) needs GVL. So the process path from timer thread to main thread is remained.
== Other thought
I know a philosophy that `trap' should run only a tiny program, without synchronization and so on. I agree with this philosophy. Current behaveour which prohibits synchronization features helps this philosophy. But I'm not sure which is good way for Ruby.