diff options
Diffstat (limited to 'lib/monitor.rb')
| -rw-r--r-- | lib/monitor.rb | 415 |
1 files changed, 191 insertions, 224 deletions
diff --git a/lib/monitor.rb b/lib/monitor.rb index 721c51a9f5..21329a5de7 100644 --- a/lib/monitor.rb +++ b/lib/monitor.rb @@ -1,249 +1,216 @@ -=begin - -= monitor.rb +# frozen_string_literal: false +# = monitor.rb +# +# Copyright (C) 2001 Shugo Maeda <shugo@ruby-lang.org> +# +# This library is distributed under the terms of the Ruby license. +# You can freely distribute/modify this library. +# +# +# In concurrent programming, a monitor is an object or module intended to be +# used safely by more than one thread. The defining characteristic of a +# monitor is that its methods are executed with mutual exclusion. That is, at +# each point in time, at most one thread may be executing any of its methods. +# This mutual exclusion greatly simplifies reasoning about the implementation +# of monitors compared to reasoning about parallel code that updates a data +# structure. +# +# You can read more about the general principles on the Wikipedia page for +# Monitors[https://en.wikipedia.org/wiki/Monitor_%28synchronization%29]. +# +# == Examples +# +# === Simple object.extend +# +# require 'monitor.rb' +# +# buf = [] +# buf.extend(MonitorMixin) +# empty_cond = buf.new_cond +# +# # consumer +# Thread.start do +# loop do +# buf.synchronize do +# empty_cond.wait_while { buf.empty? } +# print buf.shift +# end +# end +# end +# +# # producer +# while line = ARGF.gets +# buf.synchronize do +# buf.push(line) +# empty_cond.signal +# end +# end +# +# The consumer thread waits for the producer thread to push a line to buf +# while <tt>buf.empty?</tt>. The producer thread (main thread) reads a +# line from ARGF and pushes it into buf then calls <tt>empty_cond.signal</tt> +# to notify the consumer thread of new data. +# +# === Simple Class include +# +# require 'monitor' +# +# class SynchronizedArray < Array +# +# include MonitorMixin +# +# def initialize(*args) +# super(*args) +# end +# +# alias :old_shift :shift +# alias :old_unshift :unshift +# +# def shift(n=1) +# self.synchronize do +# self.old_shift(n) +# end +# end +# +# def unshift(item) +# self.synchronize do +# self.old_unshift(item) +# end +# end +# +# # other methods ... +# end +# +# +SynchronizedArray+ implements an Array with synchronized access to items. +# This Class is implemented as subclass of Array which includes the +# MonitorMixin module. +# +module MonitorMixin + ConditionVariable = Monitor::ConditionVariable # :nodoc: -Copyright (C) 2001 Shugo Maeda <shugo@ruby-lang.org> + # + # FIXME: This isn't documented in Nutshell. + # + # Since MonitorMixin.new_cond returns a ConditionVariable, and the example + # above calls while_wait and signal, this class should be documented. + # -This library is distributed under the terms of the Ruby license. -You can freely distribute/modify this library. + def self.extend_object(obj) # :nodoc: + super(obj) + obj.__send__(:mon_initialize) + end -== example + # + # Attempts to enter exclusive section. Returns +false+ if lock fails. + # + def mon_try_enter + @mon_data.try_enter + end + # For backward compatibility + alias try_mon_enter mon_try_enter -This is a simple example. + # + # Enters exclusive section. + # + def mon_enter + @mon_data.enter + end - require 'monitor.rb' - - buf = [] - buf.extend(MonitorMixin) - empty_cond = buf.new_cond - - # consumer - Thread.start do - loop do - buf.synchronize do - empty_cond.wait_while { buf.empty? } - print buf.shift - end - end + # + # Leaves exclusive section. + # + def mon_exit + mon_check_owner + @mon_data.exit end - - # producer - while line = ARGF.gets - buf.synchronize do - buf.push(line) - empty_cond.signal - end + + # + # Returns true if this monitor is locked by any thread + # + def mon_locked? + @mon_data.mon_locked? end -The consumer thread waits for the producer thread to push a line -to buf while buf.empty?, and the producer thread (main thread) -reads a line from ARGF and push it to buf, then call -empty_cond.signal. + # + # Returns true if this monitor is locked by current thread. + # + def mon_owned? + @mon_data.mon_owned? + end -=end - -module MonitorMixin - module Accessible - protected - attr_accessor :mon_owner, :mon_count - attr_reader :mon_entering_queue, :mon_waiting_queue + # + # Enters exclusive section and executes the block. Leaves the exclusive + # section automatically when the block exits. See example under + # +MonitorMixin+. + # + def mon_synchronize(&b) + @mon_data.synchronize(&b) end - - module Initializable - protected - def mon_initialize - @mon_owner = nil - @mon_count = 0 - @mon_entering_queue = [] - @mon_waiting_queue = [] + alias synchronize mon_synchronize + + # + # Creates a new MonitorMixin::ConditionVariable associated with the + # Monitor object. + # + def new_cond + unless defined?(@mon_data) + mon_initialize + @mon_initialized_by_new_cond = true end + return ConditionVariable.new(@mon_data) end - - class ConditionVariable - class Timeout < Exception; end - - include Accessible - - def wait(timeout = nil) - if @monitor.mon_owner != Thread.current - raise ThreadError, "current thread not owner" - end - - if timeout - ct = Thread.current - timeout_thread = Thread.start { - Thread.pass - sleep(timeout) - ct.raise(Timeout.new) - } - end - - Thread.critical = true - count = @monitor.mon_count - @monitor.mon_count = 0 - @monitor.mon_owner = nil - if @monitor.mon_waiting_queue.empty? - t = @monitor.mon_entering_queue.shift - else - t = @monitor.mon_waiting_queue.shift - end - t.wakeup if t - @waiters.push(Thread.current) - begin - Thread.stop - rescue Timeout - ensure - Thread.critical = true - if timeout && timeout_thread.alive? - Thread.kill(timeout_thread) - end - if @waiters.include?(Thread.current) # interrupted? - @waiters.delete(Thread.current) - end - while @monitor.mon_owner && - @monitor.mon_owner != Thread.current - @monitor.mon_waiting_queue.push(Thread.current) - Thread.stop - Thread.critical = true - end - @monitor.mon_owner = Thread.current - @monitor.mon_count = count - Thread.critical = false - end - end - - def wait_while - while yield - wait - end - end - - def wait_until - until yield - wait - end - end - - def signal - if @monitor.mon_owner != Thread.current - raise ThreadError, "current thread not owner" - end - Thread.critical = true - t = @waiters.shift - t.wakeup if t - Thread.critical = false - Thread.pass - end - - def broadcast - if @monitor.mon_owner != Thread.current - raise ThreadError, "current thread not owner" - end - Thread.critical = true - for t in @waiters - t.wakeup - end - @waiters.clear - Thread.critical = false - Thread.pass - end - - def count_waiters - return @waiters.length - end - private - def initialize(monitor) - @monitor = monitor - @waiters = [] - end - end - - include Accessible - include Initializable - extend Initializable - - def self.extend_object(obj) - super(obj) - obj.mon_initialize - end - - def try_mon_enter - result = false - Thread.critical = true - if mon_owner.nil? - self.mon_owner = Thread.current - end - if mon_owner == Thread.current - self.mon_count += 1 - result = true - end - Thread.critical = false - return result - end - def mon_enter - Thread.critical = true - while mon_owner != nil && mon_owner != Thread.current - mon_entering_queue.push(Thread.current) - Thread.stop - Thread.critical = true - end - self.mon_owner = Thread.current - self.mon_count += 1 - Thread.critical = false + # Use <tt>extend MonitorMixin</tt> or <tt>include MonitorMixin</tt> instead + # of this constructor. Have look at the examples above to understand how to + # use this module. + def initialize(...) + super + mon_initialize end - - def mon_exit - if mon_owner != Thread.current - raise ThreadError, "current thread not owner" - end - Thread.critical = true - self.mon_count -= 1 - if mon_count == 0 - self.mon_owner = nil - if mon_waiting_queue.empty? - t = mon_entering_queue.shift - else - t = mon_waiting_queue.shift + + # Initializes the MonitorMixin after being included in a class or when an + # object has been extended with the MonitorMixin + def mon_initialize + if defined?(@mon_data) + if defined?(@mon_initialized_by_new_cond) + return # already initialized. + elsif @mon_data_owner_object_id == self.object_id + raise ThreadError, "already initialized" end end - t.wakeup if t - Thread.critical = false - Thread.pass + @mon_data = ::Monitor.new + @mon_data_owner_object_id = self.object_id end - def mon_synchronize - mon_enter - begin - yield - ensure - mon_exit - end - end - alias synchronize mon_synchronize - - def new_cond - return ConditionVariable.new(self) - end - -private - def initialize(*args) - super - mon_initialize + # Ensures that the MonitorMixin is owned by the current thread, + # otherwise raises an exception. + def mon_check_owner + @mon_data.mon_check_owner end end -class Monitor - include MonitorMixin - alias try_enter try_mon_enter - alias enter mon_enter - alias exit mon_exit - alias owner mon_owner +class Monitor # :nodoc: + alias try_mon_enter try_enter + alias mon_try_enter try_enter + alias mon_enter enter + alias mon_exit exit + alias mon_synchronize synchronize end -# Local variables: -# mode: Ruby -# tab-width: 8 -# End: +# Documentation comments: +# - All documentation comes from Nutshell. +# - MonitorMixin.new_cond appears in the example, but is not documented in +# Nutshell. +# - All the internals (internal modules Accessible and Initializable, class +# ConditionVariable) appear in RDoc. It might be good to hide them, by +# making them private, or marking them :nodoc:, etc. +# - RDoc doesn't recognise aliases, so we have mon_synchronize documented, but +# not synchronize. +# - mon_owner is in Nutshell, but appears as an accessor in a separate module +# here, so is hard/impossible to RDoc. Some other useful accessors +# (mon_count and some queue stuff) are also in this module, and don't appear +# directly in the RDoc output. +# - in short, it may be worth changing the code layout in this file to make the +# documentation easier |