Continuation called across trap

Does anyone know what the rather mysterious error "continuation called across trap" means? It's triggered when I use SyncEnumerator in a multithreaded script. I don't believe I'm doing anything obviously wrong with threads, but this error disappears if I don't use threads. Furthermore, the error seems to occur when I use irb but not ruby (?? I need to verify this). I'm suspecting there might be a bug in irb. Code to reproduce the problem is below. Note, also, that the problem disappears if you remove the use of @values.find--that is, if you call SyncEnumerator.each directly in the lambda.



require 'thread'
require 'generator'

class Region

   def initialize
     @values = []
     @work_queue =
     @thread = do
       loop do

   def add(value)
     @work_queue << lambda do
       @values << value

   def find(template)
     @work_queue << lambda do
       @values.find do |value|, value).each do |lhs, rhs|
    puts "checking: #{lhs.inspect} === #{rhs.inspect}"


Thread.abort_on_exception = true

reg =
reg.add [1,1]
reg.add [1,2]
reg.add [1,3]

reg.find [1,2]

#sleep 10 # uncommenting this somehow prevents the error

MacOS X 10.4.7
$ ruby --version
ruby 1.8.4 (2005-12-24) [powerpc-darwin8.5.0]
$ irb --prompt-mode simple
>> load 'Fail4.rb'
checking: 1 === 1=> true
/opt/local/lib/ruby/1.8/generator.rb:132:in `call': continuation called across trap (RuntimeError)
         from /opt/local/lib/ruby/1.8/generator.rb:132:in `next'
         from /opt/local/lib/ruby/1.8/generator.rb:225:in `each'
         from /opt/local/lib/ruby/1.8/generator.rb:220:in `each'
         from /opt/local/lib/ruby/1.8/generator.rb:217:in `each'
         from ./Fail4.rb:25:in `find'
         from ./Fail4.rb:2:in `find'
         from ./Fail4.rb:24:in `find'
         from ./Fail4.rb:11:in `initialize'
         from ./Fail4.rb:10:in `initialize'
         from ./Fail4.rb:9:in `initialize'
         from ./Fail4.rb:36
         from (irb):1:in `irb_binding'
         from /opt/local/lib/ruby/1.8/irb/workspace.rb:52:in `irb_binding'
         from /opt/local/lib/ruby/1.8/irb/workspace.rb:52