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Bug #6416

closed

Deadlock when calling Thread#join from signal interrupt context

Added by ender672 (Timothy Elliott) over 10 years ago. Updated almost 10 years ago.

Status:
Closed
Priority:
Normal
Target version:
ruby -v:
ruby 2.0.0dev (2012-05-09 trunk 35598) [x86_64-linux]
Backport:
[ruby-core:44956]

Description

=begin
The interpreter can deadlock when calling Thread#join both from the main context and from the signal handler context.

t = Thread.new{ sleep 3 }

Signal.trap "SIGINT" do
t.join
end

puts 'Press ctrl + c now'
t.join

The above will deadlock on linux x86_64 with ruby 1.9.x and ruby trunk. It works fine with ruby 1.8.7-p352 and JRuby.

=end

Updated by mame (Yusuke Endoh) over 10 years ago

  • Status changed from Open to Assigned
  • Assignee set to kosaki (Motohiro KOSAKI)

Kosaki-san, could you take a look?

--
Yusuke Endoh

Updated by kosaki (Motohiro KOSAKI) over 10 years ago

  • Assignee changed from kosaki (Motohiro KOSAKI) to ko1 (Koichi Sasada)

Hi ko1,

This is because thread_join() is not designed reentrant. It can insert a thread twice join_list. And then, join_list
is going to become circular ring and it lead to deadlock.

So, I think th.join in trap context should raise ThreadError. What do you think?

Updated by ko1 (Koichi Sasada) about 10 years ago

  • Target version set to 2.0.0

Please give me a time.

Updated by ko1 (Koichi Sasada) about 10 years ago

  • Assignee changed from ko1 (Koichi Sasada) to kosaki (Motohiro KOSAKI)

I agree with kosaki-san's comment.

Updated by kosaki (Motohiro KOSAKI) almost 10 years ago

  • Status changed from Assigned to Closed

Fixed at r37852.
Thanks, Timothy!

Updated by authorNari (Narihiro Nakamura) almost 10 years ago

Hello

I need sometimes to call Thread#join in Signal.trap when I want to implement safe termination in a server.
For instance: https://gist.github.com/4158509

Is it a wrong use case in the first place?

Thanks.

Updated by kosaki (Motohiro KOSAKI) almost 10 years ago

Nari,

In your case, main thread and trap handler uses the same mutex and it is racy and deadlockable. Even if I revert my change, it wouldn't work.

Updated by authorNari (Narihiro Nakamura) almost 10 years ago

kosaki (Motohiro KOSAKI) wrote:

Nari,

In your case, main thread and trap handler uses the same mutex and it is racy and deadlockable. Even if I revert my change, it wouldn't work.

I see, Thanks!

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