From: "ibc (Iñaki Baz Castillo)" <ibc@...>
Date: 2012-05-15T07:59:47+09:00
Subject: [ruby-core:45043] [ruby-trunk - Bug #6433] rb_thread_blocking_region(): ubf() function is executed with GVL


Issue #6433 has been updated by ibc (I��aki Baz Castillo).


ko1 (Koichi Sasada) wrote:
>  Okay, maybe I understand your problem.
>  
>  Let us clear them:
>  (1) There are several threads and main threads
>  (2) main thread kills another blocking thread
>  
>  Right?
>  
>  In this case, ubf() will be called by a thread "Thread#kill" (or signal,
>  etc).  Main thread has GVL, and call ubf() to cancel another thread.
>  This is why the error occurs.
>  
>  FYI:
>  >> /usr/lib/libruby-1.9.1.so.1.9(rb_thread_kill+0x48) [0x7fdcfff680a8]
>  is Thread#kill code.
>  
>  Maybe you expect that ubf() was called by *blocking* thread.  However,
>  it is not.

Hi, within my ubf() function I printf the value of ruby_thread_has_gvl_p() and I get 1.


>  In last comment, I made a mistake that "ubf() is not called with GVL".
>  It's my mistake.  Correct answer is "ubf() is possible to be called
>  with/without GVL".
>  
>  We can't use "call_with_gvl()" in ubf().

Clear.  



>  You need call shutdown/destruct codes *after* unblocking.

That is what I don't understand. How to call those shutdown/destruct codes *after* my ubf() function? And what should then my ubf() function do?


I've changed my code now. My ubf() function does not call to rb_thread_call_with_gvl() (since it already has the GVL). Then it "safely" invokes my AE.stop method which terminates all the UV handles. But doing that, uv_run() exits so the C code within the run_uv_without_gvl() continues and terminates (of course without the GVL). After that the program gets frozen. If I press Ctrl+C (Interrupt signal) then I see my ubf() being calling again! Also with GVL! and then the program gets really frozen (kill -9 needed).


Before you said: "Maybe you shouldn't use Ruby code (Ruby code can be run after blocking process is canceled)".

What do you exactly mean? Where to put that Ruby code?

Thanks a lot.
----------------------------------------
Bug #6433: rb_thread_blocking_region(): ubf() function is executed with GVL
https://bugs.ruby-lang.org/issues/6433#change-26625

Author: ibc (I��aki Baz Castillo)
Status: Open
Priority: Normal
Assignee: 
Category: ext
Target version: 1.9.2
ruby -v: ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-linux]


thread.c says:

------------------------
 *   If another thread interrupts this thread (Thread#kill, signal delivery,
 *   VM-shutdown request, and so on), `ubf()' is called (`ubf()' means
 *   "un-blocking function").  `ubf()' should interrupt `func()' execution.

 *   NOTE: You can not execute most of Ruby C API and touch Ruby
 *         objects in `func()' and `ubf()', including raising an
 *         exception, because current thread doesn't acquire GVL
 *         (cause synchronization problem).

VALUE
rb_thread_blocking_region(
   rb_blocking_function_t *func, void *data1,
   rb_unblock_function_t *ubf, void *data2)

--------------------------


I've created my ubf() function which is called when the Ruby thread in which rb_thread_blocking_region() was called is killed or interrupted. Within my ubf() function I expect not to have the GVL (as the doc says) and I need to run Ruby code, so I use:

  rb_thread_call_with_gvl(terminate_my_C_reactor_with_gvl, NULL);

and I get an error:

 [BUG] rb_thread_call_with_gvl: called by a thread which has GVL.

So... is ubf() called with the GVL or not??


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