From: Dave Thomas <dave@...>
Date: 2006-01-17T05:33:38+09:00
Subject: There's a deadlock in code in the PickAxe, and I'm not seeing why:

The following code (form pg. 739) deadlocks with a large count. What  
am I missing?

Cheers


Dave




require 'thwait'
require 'sync'

class Counter
   attr_reader :total_count
   def initialize
     @total_count = 0
     @count_down = 0
     @sync = Sync.new
   end
   def inc
     @sync.synchronize(:EX) do
       @total_count += 1
       @count_down -= 1
     end
   end
   def test_consistent
     @sync.synchronize(:SH) do
       fail "Bad counts" unless @total_count + @count_down == 0
     end
   end
end

count = Counter.new
waiter = ThreadsWait.new([])

# create 10 threads that each inc() 10,000 times
10.times do
   waiter.join_nowait(Thread.new { 100_000.times do
     count.inc
     count.test_consistent
   end })
end

p waiter.all_waits
p count.total_count