syncthreads.rb

require 'thread'

$done = {}
$size = 2
$mutex = Mutex.new
$resource = ConditionVariable.new

def register(thread)
  id = thread.object_id
  $mutex.synchronize do
    $resource.wait($mutex)
    $done[id] = false
    $resource.broadcast($mutex)
  end
  while $done.size != $size
    sleep 0.001
  end
end

def done(thread)
  id = thread.object_id
  $mutex.synchronize do
    $resource.wait($mutex)
    $done[id] = true
    $resource.broadcast($mutex)
  end
end

def syncthreads
  until $done.all? { |x| x[1] == true}
    print $done
    sleep 0.00001
  end
  $done.each do |k,v|
    $done[k] = false
  end
end

x = 0

a = Thread.new do
  register(Thread.current)
  x = 1
  done(Thread.current)
  syncthreads()
end

b = Thread.new do
  register(Thread.current)
  # do nothing
  done(Thread.current)
  syncthreads()
  if x == 0
    raise "Lol"
  end
end

x = 0
[a,b].each { |t| t.join }