# Weird deadlock problems with Slave/drb

**URL:** <https://www.ruby-forum.com/t/weird-deadlock-problems-with-slave-drb/108201>\
**Category:** Ruby\
**Created:** [June 29, 2007, 11:22pm UTC](https://www.ruby-forum.com/t/weird-deadlock-problems-with-slave-drb/108201 "2007-06-29T23:22:53Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![Peter\_Lichten](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/d9b06d/32.png) [@Peter\_Lichten](https://www.ruby-forum.com/u/Peter_Lichten)\
**Post date:** [June 29, 2007, 11:22pm UTC](https://www.ruby-forum.com/t/weird-deadlock-problems-with-slave-drb/108201/1 "2007-06-29T23:22:53Z")

</div>

#!/usr/bin/env ruby

# Original program idea:

# Write a ruby program that checks the integrity of all my FLAC music

files,

# and that makes use of my MacBooks Core Duo CPU. Since Ruby doesn’t

support

# native threadds, I decided to use the Slave library.

# 

# Problem:

# I start 3 Slave servers:

# worker1 and worker2 both query the filename server to get the next

filename

# to process.

# 

# On Mac OS 10.4.10, ruby 1.8.6 (Locomotive or MacPorts, same problem)

the second

# worker server process never starts, it seems to sleep forver, and I

don’t

# see my programming mistake.

# 

# The same problem occurs on Ubuntu Feisty.

# 

# However: IF you start the 2nd worker after the first worker completed

its

# work, it runs without problem.

# 

# And: If you disable the call to the filename server, both workers run

# in parallel, too, without deadlocking.

# 

# So the problem has something to do with both workers trying to access

the

# same filename server.

# 

# Any ideas?

require ‘slave’  
require ‘monitor’  
require ‘fastthread’

class FlacTestServer

def processFiles(filenameServer)  
50.times do |i|  
#sleep(0.02)  
#Activate this:  
#puts(“PID #{ Process.pid }: Iteration #{ i }”)  
#and disable this and both workers will run without worker 2  
sleeping forever.  
puts("#{ Process.pid }: #{ filenameServer.nextFilename() }")  
end  
end  
end

class FilenameServer  
include MonitorMixin

def initialize()  
super  
@counter = 0  
end

def nextFilename()  
synchronize do  
# Return some dummy data  
@counter += 1  
“#{ Process.pid }, #{ @counter }”  
end  
end  
end

if $0 == **FILE**

fnServer = Slave.new() { FilenameServer.new() }.object

worker1 = Slave.object({:async =\> true, :psname =\> ‘Worker1’}) {  
FlacTestServer.new().processFiles(fnServer) }

# “Works” if you activate this:

#worker1.join()

worker2 = Slave.object({:async =\> true, :psname =\> ‘Worker2’}) {  
FlacTestServer.new().processFiles(fnServer) }

# If you create the slaves using the following method instead, worker2

sometimes runs, sometimes not

# and sometimes it runs only a few internal iterations before it

sleeps forever / deadlocks…?!?

# But you can get it to work if you active the sleep call in line 37.

#ftServer1 = Slave.new() { FlacTestServer.new() }.object()  
#ftServer2 = Slave.new() { FlacTestServer.new() }.object()

# 

#worker1 = Thread.new() { ftServer1.processFiles(fnServer) }  
#worker2 = Thread.new() { ftServer2.processFiles(fnServer) }

worker1.join()  
puts(“Worker 1 terminated.”)

#puts(“Worker 2 status: #{ worker2.status() }”) until  
worker2.join(0.15)  
worker2.join()  
puts(“Worker 2 terminated.”)

puts(“End main program: #{Process.pid}”)  
end