Bug #9342: [PATCH] SizedQueue#clear does not notify waiting threads in Ruby 1.9.3

• Status: Closed
• Assignee: ko1 (Koichi Sasada)
• Target version: 2.2.0
• ruby -v: ruby 1.9.3p484 (2013-11-22 revision 43786) [x86_64-darwin11.4.2]
• Backport: 1.9.3: DONE, 2.0.0: DONE, 2.1: DONE

[jsc (Justin Collins)]

In Ruby 1.9.3, when SizedQueue#clear is called, it empties the queue but does not notify waiting threads that the queue is empty. This typically leads to deadlock when the queue is full.

For example:

sq = SizedQueue.new(1)
sq << 1 # Fill queue

t1 = Thread.new do
sq << 1 # Attempt to add another item to queue, fail and go to sleep waiting
end

t2 = Thread.new do
Thread.pass
sq.clear
end

t2.join # Empty queue
t1.join # Deadlock, t1 continues to sleep

[jsc (Justin Collins)]

• File 0002-Wake-waiting-threads-when-SizedQueue-clear-is-called-2.0.patch 0002-Wake-waiting-threads-when-SizedQueue-clear-is-called-2.0.patch added

Looks like this is also a problem in 2.0.0, although the implementation is a little different. Attaching patch for 2.0.0 too although it's probably clear.

[normalperson (Eric Wong)]

I agree this is a problem. This also affects 2.1.0 and trunk (where
SizedQueue is C).

[ko1 (Koichi Sasada)]

• Category set to ext
• Assignee set to ko1 (Koichi Sasada)
• Target version set to 2.2.0

• Status changed from Open to Closed
• % Done changed from 0 to 100

Applied in changeset r44595.

---

• ext/thread/thread.c (rb_szqueue_clear): notify SZQUEUE_WAITERS
  on SizedQueue#clear. [ruby-core:59462] [Bug #9342]

• test/thread/test_queue.rb: add test. the patch is from
  Justin Collins.

[jsc (Justin Collins)]

Thank you!

As far as I can tell, SizedQueue#clear has never notified waiting threads since it was introduced in Ruby 1.4. Perhaps something with green threads allowed it to work anyway? It is definitely an issue in 1.9.3 and later.

[usa (Usaku NAKAMURA)]

• Backport changed from 1.9.3: UNKNOWN, 2.0.0: UNKNOWN, 2.1: UNKNOWN to 1.9.3: REQUIRED, 2.0.0: REQUIRED, 2.1: REQUIRED

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 1.9.3: REQUIRED, 2.0.0: REQUIRED, 2.1: REQUIRED to 1.9.3: REQUIRED, 2.0.0: DONE, 2.1: REQUIRED

1.9.3 and 2.0.0 has different implementation of Queue/SizedQueue from 2.1/trunk.
I partially backported r44595 for test, and commited a patch for ruby_2_0_0 at r44899.

[usa (Usaku NAKAMURA)]

• Backport changed from 1.9.3: REQUIRED, 2.0.0: DONE, 2.1: REQUIRED to 1.9.3: DONE, 2.0.0: DONE, 2.1: REQUIRED

Commited to ruby_1_9_3 at r44932.
Thank you, Justin!

[naruse (Yui NARUSE)]

• Backport changed from 1.9.3: DONE, 2.0.0: DONE, 2.1: REQUIRED to 1.9.3: DONE, 2.0.0: DONE, 2.1: DONE

r45104.