Bug #6416: Deadlock when calling Thread#join from signal interrupt context

• Status: Closed
• Priority: Normal
• Assignee: kosaki (Motohiro KOSAKI)
• Target version: 2.0.0
• ruby -v: ruby 2.0.0dev (2012-05-09 trunk 35598) [x86_64-linux]

[ender672 (Timothy Elliott)]

=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

[mame (Yusuke Endoh)]

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

Kosaki-san, could you take a look?

--
Yusuke Endoh [e-mail]

[kosaki (Motohiro KOSAKI)]

• 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?

[ko1 (Koichi Sasada)]

• Target version set to 2.0.0

Please give me a time.

[ko1 (Koichi Sasada)]

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

I agree with kosaki-san's comment.

[kosaki (Motohiro KOSAKI)]

• Status changed from Assigned to Closed

Fixed at r37852.
Thanks, Timothy!

[authorNari (Narihiro Nakamura)]

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.

[kosaki (Motohiro KOSAKI)]

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.

[authorNari (Narihiro Nakamura)]

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!