From: "Iñaki Baz Castillo" <ibc@...>
Date: 2012-05-22T09:31:57+09:00
Subject: Re: [C ext and GVL] Why UBF() is called even if Ruby traps signals ??

2012/5/22 Eric Wong <normalperson@yhbt.net>:
> Iñaki Baz Castillo <ibc@aliax.net> wrote:

>> After experiments, the ubf() is called in those cases:
>>
>> 1) The thread running the blocking region is killed with Thread#kill.
>>
>> 2) An interrupt for which trap(SIGNAL_NAME, "SIG_INT") has NOT been
>> set arrives while the process is blocked in the blocking region. If
>> the signal has a handler in Ruby land then ubf() is always called(
>> regardless the trap handler will terminate the program or not !!!).
>
> Yes, otherwise for a single-threaded Ruby application, signal handlers
> have only one thread to fire in (so it needs to interrupt uv_run()).

Therefore I cannot use the ubf() for nothing. Typicall my code will be
single thread (see explanation below please).



>> Badly, in any of those cases, if
>> rb_thread_interrupted(rb_thread_current()) is called within the ubf()
>> function it returns false, so honestly I have no idea of  how to react
>> when my ubf() is called. If it's due to a signal I want it to be
>> treated in Ruby land. If it's a Thread#kill then I need to do my stuff
>> within the ubf() function. I see no way.
>
> With the self-pipe trick, your ubf() will probably just be:
>
>        /* write one \0 byte */
>        write(pipe_wfd, "", 1);
>
> Where the other end of that pipe is being watched by uv_run()
> (installed like any other IO object you're watching for).


But that's not my problem. In fact, I have a mechanism to communicate
with UV loop at any time safely from any thread:

  uv_async_send()   (thread safe)

So from the ubf() function I have no problem in telling UV "please do
this now or in your next instant iteration". My problem is: what to
say?

1) If ubf() has been called from Thread#kill then I need to run a
function that closes all the active UV handlers so uv_run() exits.

2) If ubf() has been called due to a signal receipt, I don't want
uv_run() to exit. Instead the signal wakeups the UV loop and generates
an iteration in which I call to rb_check_interrupts() for handling the
signal in Ruby land and I'm happy. But the ubf() has been called !!!

So the problem is that when a signal is received, it makes the ubf()
function to be called and, at that point, I have no way to know,
within the ubf() function, whether it has been called by Thread#kill
or by a received signal.


Thanks a lot.



-- 
Iñaki Baz Castillo
<ibc@aliax.net>