sync_lock

# File lib/sync.rb, line 138
  def sync_lock(m = EX)
    return unlock if m == UN

    while true
      @sync_mutex.synchronize do
        if sync_try_lock_sub(m)
          return self
        else
          if sync_sh_locker[Thread.current]
            sync_upgrade_waiting.push [Thread.current, sync_sh_locker[Thread.current]]
            sync_sh_locker.delete(Thread.current)
          else
            sync_waiting.push Thread.current
          end
          @sync_mutex.sleep
        end
      end
    end
    self
  end