# Thread deadlock

**URL:** <https://www.ruby-forum.com/t/thread-deadlock/225969>\
**Category:** Ruby\
**Created:** [September 18, 2007, 6:11am UTC](https://www.ruby-forum.com/t/thread-deadlock/225969 "2007-09-18T06:11:49Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [September 18, 2007, 6:11am UTC](https://www.ruby-forum.com/t/thread-deadlock/225969/1 "2007-09-18T06:11:49Z")

</div>

I wanted to create a thread pool. I know I could have used a  
SizedQueue in the thread pool, but I wanted to later on change the  
thread queue to a priority queue.

With ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-cygwin] I get a  
deadlock error. ruby 1.8.5 (2006-08-25) [i386-mswin32] is not giving  
me that error. I think that my code is written correctly and that  
this may be a bug in the version/build of ruby I am running on. Does  
anybody see a problem with this code? Thanks.

require ‘thread’

class ThreadPool

def initialize(thread\_size=10, queue\_size=100)  
@mutex = Mutex.new  
@cv = ConditionVariable.new  
@queue = []  
@max\_queue\_size = queue\_size  
@threads = []  
thread\_size.times { @threads \<\< Thread.new { start\_worker } }  
end

def add\_work(\*args, &callback)  
push\_task(Task.new(\*args, &callback))  
end

def push\_task(task)  
puts “#{Thread.current}|push\_task|sync on @mutex”  
@mutex.synchronize do  
while @max\_queue\_size \> 0 && @queue.size \>= @max\_queue\_size do  
puts “#{Thread.current}|push\_task|wait on @mutex”  
@cv.wait(@mutex)  
end  
@queue.push(task)  
puts “#{Thread.current}|execute|broadcast on @mutex”  
@cv.broadcast  
end  
puts “#{Thread.current}|push\_task|done with sync on @mutex”  
task  
end

def pop\_task  
task = nil  
puts “#{Thread.current}|pop\_task|sync on @mutex”  
@mutex.synchronize do  
while @queue.size == 0 do  
puts “#{Thread.current}|pop\_task|wait on @mutex”  
@cv.wait(@mutex)  
end  
task = @queue.shift  
puts “#{Thread.current}|execute|broadcast on @mutex”  
@cv.broadcast  
end  
puts “#{Thread.current}|pop\_task|done with sync on @mutex”  
task  
end

def start\_worker  
puts “#{Thread.current} running worker”  
while true  
task = pop\_task  
return if task == :stop  
task.execute  
end  
end

class Task

```
attr_reader :result, :exception

def initialize(*args, &callback)
  @args = args
  @callback = callback
  @done = false
  @result = nil
  @exception = nil
  @mutex = Mutex.new
  @cv = ConditionVariable.new
end

def execute
  begin
    @result = @callback.call(*@args)
  rescue Exception => e
    @exception = e

```

STDERR.puts “Error in thread #{Thread.current} - #{e}”  
e.backtrace.each { |element| STDERR.puts(element) }  
end  
puts “#{Thread.current}|execute|sync on @mutex”  
@mutex.synchronize do  
@done = true  
puts “#{Thread.current}|execute|broadcast on @mutex”  
@cv.broadcast  
end  
puts “#{Thread.current}|execute|done with sync on @mutex”  
end

```
def join
  puts "#{Thread.current}|join|sync on @mutex"
  @mutex.synchronize do
    while !@done
      puts "#{Thread.current}|join|wait on @mutex"
@cv.wait(@mutex)
    end
  end
  puts "#{Thread.current}|join|done with sync on @mutex"
end

```

end

end

tasks = []  
tp = ThreadPool.new(3, 10)  
sleep(1)  
100.times do |id|  
STDERR.puts “adding work”  
tasks \<\< tp.add\_work do  
puts “Running #{id} #{Thread.current}”  
sleep 2  
puts “Ending #{id} #{Thread.current}”  
Time.now  
end  
end

puts “Waiting for tasks to complete”  
tasks.each do |task|  
task.join  
if !task.exception.nil?  
puts “Failed task - #{task.exception}”  
else  
puts “Result - #{task.result}”  
end  
end

## output:

$ ruby -v  
ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-cygwin]  
[/users/bcastill/tpool]  
$ ruby thread\_pool.rb  
#Thread:0x1002b63c running worker  
#Thread:0x1002b63c|pop\_task|sync on @mutex  
#Thread:0x1002b63c|pop\_task|wait on @mutex  
#Thread:0x1002b4fc running worker  
#Thread:0x1002b4fc|pop\_task|sync on @mutex  
#Thread:0x1002b4fc|pop\_task|wait on @mutex  
#Thread:0x1002b3d0 running worker  
#Thread:0x1002b3d0|pop\_task|sync on @mutex  
#Thread:0x1002b3d0|pop\_task|wait on @mutex  
adding work  
#Thread:0x1003c964|push\_task|sync on @mutex  
#Thread:0x1003c964|execute|broadcast on @mutex  
#Thread:0x1002b3d0|execute|broadcast on @mutex  
#Thread:0x1003c964|push\_task|done with sync on @mutex  
adding work  
#Thread:0x1003c964|push\_task|sync on @mutex  
#Thread:0x1002b4fc|pop\_task|wait on @mutex  
#Thread:0x1002b3d0|pop\_task|done with sync on @mutex  
Running 0 #Thread:0x1002b3d0  
Ending 0 #Thread:0x1002b3d0  
#Thread:0x1002b3d0|execute|sync on @mutex  
#Thread:0x1002b3d0|execute|broadcast on @mutex  
#Thread:0x1002b3d0|execute|done with sync on @mutex  
#Thread:0x1002b3d0|pop\_task|sync on @mutex  
#Thread:0x1002b3d0|pop\_task|wait on @mutex  
deadlock 0x1002b4fc: sleep:- - thread\_pool.rb:39  
deadlock 0x1002b63c: sleep:- - thread\_pool.rb:39  
deadlock 0x1003c964: sleep:- (main) - thread\_pool.rb:20  
deadlock 0x1002b3d0: sleep:- - thread\_pool.rb:39  
thread\_pool.rb:39:in `push_task': Thread(0x1002b3d0): deadlock (fatal) from thread_pool.rb:15:in`add\_work’  
from thread\_pool.rb:109  
from thread\_pool.rb:107:in `times’  
from thread\_pool.rb:107

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [September 18, 2007, 6:41pm UTC](https://www.ruby-forum.com/t/thread-deadlock/225969/2 "2007-09-18T18:41:01Z")

</div>

On Sep 17, 9:09 pm, removed\_email\_address@domain.invalid wrote:

> I wanted to create a thread pool. I know I could have used a  
> SizedQueue in the thread pool, but I wanted to later on change the  
> thread queue to a priority queue.
> 
> With ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-cygwin] I get a  
> deadlock error. ruby 1.8.5 (2006-08-25) [i386-mswin32] is not giving  
> me that error. I think that my code is written correctly and that  
> this may be a bug in the version/build of ruby I am running on. Does  
> anybody see a problem with this code? Thanks.

I’ve tried using some different version of ruby to see if the code  
works or not:

## Failed versions:

ruby 1.8.6 (2007-03-13 patchlevel 0) [i686-linux]  
ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-cygwin]  
ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-mswin32]

## Working versions:

ruby 1.8.5 (2006-08-25) [i386-mswin32]  
ruby 1.8.5 (2007-08-27 rev 4201) [x86-jruby1.0.1]  
ruby 1.8.3 (2005-09-21) [i686-linux]  
ruby 1.9.0 (2007-09-15 patchlevel 0) [i386-cygwin]

It seems to me like there is something wrong with the latest stable  
version of ruby.

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [September 18, 2007, 8:22pm UTC](https://www.ruby-forum.com/t/thread-deadlock/225969/3 "2007-09-18T20:22:29Z")

</div>

On Sep 18, 10:43 am, MenTaLguY [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> On Wed, 19 Sep 2007 01:40:08 +0900, removed\_email\_address@domain.invalid wrote:
> 
> > It seems to me like there is something wrong with the latest stable  
> > version of ruby.
> 
> 1.8.6-p0 is broken, but it is not the most recent stable release.
> 
> The latest stable release is 1.8.6-p36.
> 
> -mental

I received the error with the stable recommended version from  
[Download Ruby](http://www.ruby-lang.org/en/downloads/).  
Should I be using the stable snapshot?

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [September 18, 2007, 7:44pm UTC](https://www.ruby-forum.com/t/thread-deadlock/225969/4 "2007-09-18T19:44:20Z")

</div>

On Wed, 19 Sep 2007 01:40:08 +0900, removed\_email\_address@domain.invalid wrote:

> It seems to me like there is something wrong with the latest stable  
> version of ruby.

1.8.6-p0 is broken, but it is not the most recent stable release.

The latest stable release is 1.8.6-p36.

-mental

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [September 18, 2007, 11:31pm UTC](https://www.ruby-forum.com/t/thread-deadlock/225969/5 "2007-09-18T23:31:04Z")

</div>

On Sep 18, 12:05 pm, MenTaLguY [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> On Wed, 19 Sep 2007 03:20:07 +0900, removed\_email\_address@domain.invalid wrote:
> 
> > I received the error with the stable recommended version from  
> > [Download Ruby](http://www.ruby-lang.org/en/downloads/).
> 
> Hmm. It looks like that is different from p36 (the file size is different):
> 
> ftp://ftp.ruby-lang.org/pub/ruby/1.8/
> 
> Try the -p36 tarball and see if it makes a difference (it should, based  
> on others’ experience).

Yes, p36 works fine. I should have done a search for deadlocks on this  
group before posting.

[http://groups.google.com/group/comp.lang.ruby/browse\_thread/thread/ec5fbc1b970d40f6/9f80264e115a1235?lnk=gst&q=thread+deadlock&rnum=3#9f80264e115a1235](http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/ec5fbc1b970d40f6/9f80264e115a1235?lnk=gst&q=thread+deadlock&rnum=3#9f80264e115a1235)

> Perhaps someone running the site needs to be more diligent about what is  
> offered for download.

That does concern me. The windows binary on  
[http://www.ruby-lang.org/en/downloads/](http://www.ruby-lang.org/en/downloads/)  
points to p0 as well.

Is it a problem with updating the web page or should those links be  
soft links to the latest 1.8.6 version?

Here is the directory listing from the ftp server in /pub/ruby

lrwxrwxrwx 1 1014 100 26 Aug 02 12:16 ruby-1.8.6-  
p36.tar.bz2 → 1.8/ruby-1.8.6-p36.tar.bz2  
lrwxrwxrwx 1 1014 100 25 Aug 02 12:16 ruby-1.8.6-  
p36.tar.gz → 1.8/ruby-1.8.6-p36.tar.gz  
lrwxrwxrwx 1 1014 100 22 Aug 02 12:16 ruby-1.8.6-  
p36.zip → 1.8/ruby-1.8.6-p36.zip  
lrwxrwxrwx 1 1000 100 22 Mar 12 2007  
ruby-1.8.6.tar.bz2 → 1.8/ruby-1.8.6.tar.bz2  
lrwxrwxrwx 1 1000 100 21 Mar 12 2007  
ruby-1.8.6.tar.gz → 1.8/ruby-1.8.6.tar.gz  
lrwxrwxrwx 1 1000 100 18 Mar 12 2007 ruby-1.8.6.zip  
 → 1.8/ruby-1.8.6.zip

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [September 18, 2007, 9:06pm UTC](https://www.ruby-forum.com/t/thread-deadlock/225969/6 "2007-09-18T21:06:42Z")

</div>

On Wed, 19 Sep 2007 03:20:07 +0900, removed\_email\_address@domain.invalid wrote:

> I received the error with the stable recommended version from  
> [Download Ruby](http://www.ruby-lang.org/en/downloads/).

Hmm. It looks like that is different from p36 (the file size is  
different):

ftp://ftp.ruby-lang.org/pub/ruby/1.8/

Try the -p36 tarball and see if it makes a difference (it should, based  
on others’ experience).

Perhaps someone running the site needs to be more diligent about what is  
offered for download.

-mental

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [September 19, 2007, 5:41am UTC](https://www.ruby-forum.com/t/thread-deadlock/225969/7 "2007-09-19T05:41:32Z")

</div>

On Sep 18, 2:28 pm, removed\_email\_address@domain.invalid wrote:

> > Try the -p36 tarball and see if it makes a difference (it should, based  
> > That does concern me. The windows binary onhttp://www.ruby-lang.org/en/downloads/  
> > points to p0 as well.

I sent an email to the webmaster at [www.ruby-lang.org](http://www.ruby-lang.org) about having p0  
for the main download links, while p36 seems to be the stable one.

## My Email

On the downloads page [Download Ruby](http://www.ruby-lang.org/en/downloads/), there  
are links to 1.8.6 recommended versions of ruby that may not be the  
latest stable version for 1.8.6. I recently ran into a bug with the  
versions of ruby currently linked to on the download page, that was  
fixed in 1.8.6-p36. I was wondering if the download page should be  
updated to the URLS listed below.

Ruby 1.8.6 Source:  
ftp://ftp.ruby-lang.org/pub/ruby/ruby-1.8.6-p36.tar.gz

Windows 1.8.6 binary:  
ftp://ftp.ruby-lang.org/pub/ruby/binaries/mswin32/ruby-1.8.6-p36-i386-mswin32.zip

Here is a link to a thread in comp.lang.ruby, where someone pointed  
out I should be using 1.8.6-p36.

## [http://groups.google.com/group/comp.lang.ruby/browse\_thread/thread/101b347655febbf0/43e0ed11f8117add?lnk=raot#43e0ed11f8117add](http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/101b347655febbf0/43e0ed11f8117add?lnk=raot#43e0ed11f8117add)

Here is the response from the web master, James.

## Response

## Does any one know who put these versions up? I don’t want to undo something we’ve done. Do we know what releases these actually are? Thanks for the information.

So, I’d like to put his question out to to the mailing list. Should  
1.8.6-p36 be the recommended stable release for ruby?

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [September 21, 2007, 6:16am UTC](https://www.ruby-forum.com/t/thread-deadlock/225969/8 "2007-09-21T06:16:38Z")

</div>

On Wed, 2007-09-19 at 13:15 +0900, removed\_email\_address@domain.invalid wrote:

> I think I will stick to using Monitor for future code.

I’d strongly recommend against using Monitor – it is slow and has some  
subtle bugs. Have you considered using fastthread?

-mental

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [September 19, 2007, 6:16am UTC](https://www.ruby-forum.com/t/thread-deadlock/225969/9 "2007-09-19T06:16:34Z")

</div>

On Sep 18, 10:43 am, MenTaLguY [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> On Wed, 19 Sep 2007 01:40:08 +0900, removed\_email\_address@domain.invalid wrote:
> 
> > It seems to me like there is something wrong with the latest stable  
> > version of ruby.
> 
> 1.8.6-p0 is broken, but it is not the most recent stable release.
> 
> The latest stable release is 1.8.6-p36.
> 
> -mental

Even though 1.8.6-p0 was not working with Mutex/ConditionVariable, I  
changed the code to use the Monitor class. I did not receive the  
error even in 1.8.6-p0.

I found this post about the differences between Mutex and Monitor.

[http://groups.google.com/group/comp.lang.ruby/browse\_frm/thread/c0a42e72de6f36de/0412d7952937abd8?lnk=gst&q=Monitor+vs+Mutex&rnum=1#0412d7952937abd8](http://groups.google.com/group/comp.lang.ruby/browse_frm/thread/c0a42e72de6f36de/0412d7952937abd8?lnk=gst&q=Monitor+vs+Mutex&rnum=1#0412d7952937abd8)

I think I will stick to using Monitor for future code.

Here is the code that works on 1.8.6-p0:

require ‘thread’  
require ‘monitor’

class ThreadPool

class PoolStopped \< Exception; end

def initialize(thread\_size=10, queue\_size=100)  
@mutex = Monitor.new  
@cv = @mutex.new\_cond  
@queue = []  
@max\_queue\_size = queue\_size  
@threads = []  
@stopped = false  
thread\_size.times { @threads \<\< Thread.new { start\_worker } }  
end

def add\_work(\*args, &callback)  
push\_task(Task.new(\*args, &callback))  
end

def push\_task(task)  
@mutex.synchronize do  
raise PoolStopped.new if @stopped  
@cv.wait\_while { @max\_queue\_size \> 0 && @queue.size \>=  
@max\_queue\_size }  
@queue.push(task)  
@cv.broadcast  
end  
task  
end

def pop\_task  
task = nil  
@mutex.synchronize do  
@cv.wait\_while { @queue.size == 0 }  
task = @queue.shift  
@cv.broadcast  
end  
task  
end

def shutdown  
@mutex.synchronize do  
@stopped = true  
@threads.each { @queue.push(:stop) }  
@cv.broadcast  
end  
@threads.each { |thread| thread.join }  
end

def start\_worker  
while true  
task = pop\_task  
return if task == :stop  
task.execute  
end  
end

# wait for current work to complete

def sync  
tasks = @mutex.synchronize { @queue.dup }  
tasks.each { |task| task.join }  
end

class Task

```
attr_reader :result, :exception

def initialize(*args, &callback)
  @args = args
  @callback = callback
  @done = false
  @result = nil
  @exception = nil
  @mutex = Monitor.new
  @cv = @mutex.new_cond
end

def execute
  begin
    @result = @callback.call(*@args)
  rescue Exception => e
    @exception = e

```

STDERR.puts “Error in thread #{Thread.current} - #{e}”  
e.backtrace.each { |element| STDERR.puts(element) }  
end  
@mutex.synchronize do  
@done = true  
@cv.broadcast  
end  
end

```
def join
  @mutex.synchronize { @cv.wait_until { @done } }
end

```

end

end

tasks = []  
tp = ThreadPool.new(10, 1000)  
sleep(1)  
100.times do |id|  
STDERR.puts “adding work”  
tasks \<\< tp.add\_work do  
puts “Running #{id} #{Thread.current}”  
sleep 5  
puts “Ending #{id} #{Thread.current}”  
end  
end

puts “Waiting for shutdown”  
tp.shutdown  
puts “done”