Backport #5342: ConditionVariable can wake a Thread that is no longer waiting on it

• Status: Rejected
• Assignee: yugui (Yuki Sonoda)

[mperham (Mike Perham)]

See gist at https://gist.github.com/1228184 for a reproducible test case.

Sequence is like this:

• Main thread spawns Thread 1. Thread 1 pauses 0.5 seconds and then signals cond variable 1.
• Main thread waits on cond variable 1 and times out after 0.3 seconds
• Main thread spawns Thread 2. Thread 2 pauses 0.5 seconds and then signals cond variable 2.
• Main thread waits on cond variable 2 with a timeout of 1.0 seconds.

I would expect this test to take 0.8 seconds. Instead the main thread is woken by the original cond variable 1 after 0.5 seconds total.

The code works as expected on JRuby 1.6.4.

[normalperson (Eric Wong)]

Mike Perham [e-mail] wrote:

ruby -v: ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin10.8.0]

See gist at https://gist.github.com/1228184 for a reproducible test case.

I can confirm the test case fails on 1.9.2-p290 on x86_32 Linux, too.

ruby_1_9_3 r33290 appears good, however. The GVL was reimplemented for
1.9.3 to improve fairness and performance, so there are likely bugs
fixed along the way.

[kosaki (Motohiro KOSAKI)]

• Tracker changed from Bug to Backport
• Project changed from Ruby master to Backport192
• Status changed from Open to Assigned
• Assignee set to yugui (Yuki Sonoda)

[kosaki (Motohiro KOSAKI)]

Hi

2011/9/20 Eric Wong [e-mail]:

Mike Perham [e-mail] wrote:

ruby -v: ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-darwin10.8.0]

See gist at https://gist.github.com/1228184 for a reproducible test case.

I can confirm the test case fails on 1.9.2-p290 on x86_32 Linux, too.

ruby_1_9_3 r33290 appears good, however.  The GVL was reimplemented for
1.9.3 to improve fairness and performance, so there are likely bugs
fixed along the way.

The bug was fixed by following commit. (r27711)
It haven't backported 1.9.2 yet.

commit f4053cf5554deb0051aabfc90180784236f1f25b
Author: mame mame@b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Date: Sun May 9 17:10:18 2010 +0000

 * lib/thread.rb (ConditionVariable#wait): ensure to remove the current
   thread from waiters.  [ruby-core:29835]

 git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@27711

b2dd03c8-39d4-4d8f-98ff-823fe69b080e

diff --git a/ChangeLog b/ChangeLog
index 7677a70..91c0e41 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon May 10 02:07:20 2010 Yusuke Endoh [e-mail]
+

•   * lib/thread.rb (ConditionVariable#wait): ensure to remove the current
  

•     thread from waiters.  [ruby-core:29835]
  

Mon May 10 00:54:15 2010 Nobuyoshi Nakada [e-mail]

     * ext/io/console/console.c (console_set_raw): new method.

diff --git a/lib/thread.rb b/lib/thread.rb
index f3831a7..88f834c 100644
--- a/lib/thread.rb
+++ b/lib/thread.rb
@@ -69,6 +69,10 @@ class ConditionVariable
@waiters.push(Thread.current)
end
mutex.sleep timeout

• ensure

•  @waiters_mutex.synchronize do
  

•    @waiters.delete(Thread.current)
  

•  end
  

  end
  self
  end

[naruse (Yui NARUSE)]

• Status changed from Assigned to Rejected