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Diffstat (limited to 'lib/monitor.rb')
| -rw-r--r-- | lib/monitor.rb | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/lib/monitor.rb b/lib/monitor.rb new file mode 100644 index 0000000000..21329a5de7 --- /dev/null +++ b/lib/monitor.rb @@ -0,0 +1,216 @@ +# 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: + + # + # 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. + # + + def self.extend_object(obj) # :nodoc: + super(obj) + obj.__send__(:mon_initialize) + end + + # + # 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 + + # + # Enters exclusive section. + # + def mon_enter + @mon_data.enter + end + + # + # Leaves exclusive section. + # + def mon_exit + mon_check_owner + @mon_data.exit + end + + # + # Returns true if this monitor is locked by any thread + # + def mon_locked? + @mon_data.mon_locked? + end + + # + # Returns true if this monitor is locked by current thread. + # + def mon_owned? + @mon_data.mon_owned? + end + + # + # 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 + 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 + + private + + # 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 + + # 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 + @mon_data = ::Monitor.new + @mon_data_owner_object_id = self.object_id + end + + # 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 # :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 + +# 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 |