sync_lock

# File lib/sync.rb, line 137
  def sync_lock(m = EX)
    return unlock if m == UN
    Thread.handle_interrupt(StandardError => :on_blocking) do
      while true
        @sync_mutex.synchronize do
          begin
            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
                unless sync_waiting.include?(Thread.current) || sync_upgrade_waiting.reverse_each.any?{|w| w.first == Thread.current }
                  sync_waiting.push Thread.current
                end
              end
              @sync_mutex.sleep
            end
          ensure
            sync_waiting.delete(Thread.current)
          end
        end
      end
    end
    self
  end