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1eba8ecb66
and allow to initialize again when obj.dup. Suggested by Benoit Daloze. [ruby-core:88504] [Feature #15000] git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66215 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
323 lines
7.6 KiB
Ruby
323 lines
7.6 KiB
Ruby
# frozen_string_literal: false
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# = monitor.rb
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#
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# Copyright (C) 2001 Shugo Maeda <shugo@ruby-lang.org>
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#
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# This library is distributed under the terms of the Ruby license.
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# You can freely distribute/modify this library.
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#
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#
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# In concurrent programming, a monitor is an object or module intended to be
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# used safely by more than one thread. The defining characteristic of a
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# monitor is that its methods are executed with mutual exclusion. That is, at
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# each point in time, at most one thread may be executing any of its methods.
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# This mutual exclusion greatly simplifies reasoning about the implementation
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# of monitors compared to reasoning about parallel code that updates a data
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# structure.
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#
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# You can read more about the general principles on the Wikipedia page for
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# Monitors[http://en.wikipedia.org/wiki/Monitor_%28synchronization%29]
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#
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# == Examples
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#
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# === Simple object.extend
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#
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# require 'monitor.rb'
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#
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# buf = []
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# buf.extend(MonitorMixin)
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# empty_cond = buf.new_cond
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#
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# # consumer
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# Thread.start do
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# loop do
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# buf.synchronize do
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# empty_cond.wait_while { buf.empty? }
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# print buf.shift
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# end
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# end
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# end
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#
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# # producer
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# while line = ARGF.gets
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# buf.synchronize do
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# buf.push(line)
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# empty_cond.signal
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# end
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# end
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#
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# The consumer thread waits for the producer thread to push a line to buf
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# while <tt>buf.empty?</tt>. The producer thread (main thread) reads a
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# line from ARGF and pushes it into buf then calls <tt>empty_cond.signal</tt>
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# to notify the consumer thread of new data.
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#
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# === Simple Class include
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#
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# require 'monitor'
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#
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# class SynchronizedArray < Array
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#
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# include MonitorMixin
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#
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# def initialize(*args)
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# super(*args)
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# end
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#
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# alias :old_shift :shift
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# alias :old_unshift :unshift
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#
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# def shift(n=1)
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# self.synchronize do
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# self.old_shift(n)
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# end
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# end
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#
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# def unshift(item)
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# self.synchronize do
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# self.old_unshift(item)
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# end
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# end
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#
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# # other methods ...
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# end
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#
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# +SynchronizedArray+ implements an Array with synchronized access to items.
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# This Class is implemented as subclass of Array which includes the
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# MonitorMixin module.
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#
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module MonitorMixin
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#
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# FIXME: This isn't documented in Nutshell.
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#
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# Since MonitorMixin.new_cond returns a ConditionVariable, and the example
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# above calls while_wait and signal, this class should be documented.
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#
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class ConditionVariable
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class Timeout < Exception; end
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#
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# Releases the lock held in the associated monitor and waits; reacquires the lock on wakeup.
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#
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# If +timeout+ is given, this method returns after +timeout+ seconds passed,
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# even if no other thread doesn't signal.
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#
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def wait(timeout = nil)
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Thread.handle_interrupt(Exception => :never) do
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@monitor.__send__(:mon_check_owner)
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count = @monitor.__send__(:mon_exit_for_cond)
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begin
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Thread.handle_interrupt(Exception => :immediate) do
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@cond.wait(@monitor.instance_variable_get(:@mon_mutex), timeout)
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end
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return true
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ensure
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@monitor.__send__(:mon_enter_for_cond, count)
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end
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end
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end
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#
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# Calls wait repeatedly while the given block yields a truthy value.
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#
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def wait_while
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while yield
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wait
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end
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end
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#
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# Calls wait repeatedly until the given block yields a truthy value.
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#
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def wait_until
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until yield
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wait
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end
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end
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#
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# Wakes up the first thread in line waiting for this lock.
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#
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def signal
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@monitor.__send__(:mon_check_owner)
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@cond.signal
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end
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#
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# Wakes up all threads waiting for this lock.
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#
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def broadcast
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@monitor.__send__(:mon_check_owner)
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@cond.broadcast
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end
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private
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def initialize(monitor)
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@monitor = monitor
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@cond = Thread::ConditionVariable.new
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end
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end
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def self.extend_object(obj)
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super(obj)
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obj.__send__(:mon_initialize)
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end
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#
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# Attempts to enter exclusive section. Returns +false+ if lock fails.
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#
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def mon_try_enter
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if @mon_owner != Thread.current
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unless @mon_mutex.try_lock
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return false
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end
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@mon_owner = Thread.current
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@mon_count = 0
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end
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@mon_count += 1
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return true
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end
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# For backward compatibility
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alias try_mon_enter mon_try_enter
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#
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# Enters exclusive section.
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#
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def mon_enter
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if @mon_owner != Thread.current
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@mon_mutex.lock
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@mon_owner = Thread.current
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@mon_count = 0
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end
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@mon_count += 1
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end
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#
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# Leaves exclusive section.
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#
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def mon_exit
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mon_check_owner
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@mon_count -=1
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if @mon_count == 0
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@mon_owner = nil
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@mon_mutex.unlock
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end
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end
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#
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# Returns true if this monitor is locked by any thread
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#
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def mon_locked?
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@mon_mutex.locked?
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end
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#
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# Returns true if this monitor is locked by current thread.
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#
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def mon_owned?
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@mon_mutex.locked? && @mon_owner == Thread.current
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end
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#
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# Enters exclusive section and executes the block. Leaves the exclusive
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# section automatically when the block exits. See example under
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# +MonitorMixin+.
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#
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def mon_synchronize
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mon_enter
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begin
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yield
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ensure
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mon_exit
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end
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end
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alias synchronize mon_synchronize
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#
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# Creates a new MonitorMixin::ConditionVariable associated with the
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# receiver.
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#
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def new_cond
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return ConditionVariable.new(self)
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end
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private
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# Use <tt>extend MonitorMixin</tt> or <tt>include MonitorMixin</tt> instead
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# of this constructor. Have look at the examples above to understand how to
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# use this module.
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def initialize(*args)
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super
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mon_initialize
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end
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# Initializes the MonitorMixin after being included in a class or when an
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# object has been extended with the MonitorMixin
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def mon_initialize
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if defined?(@mon_mutex) && @mon_mutex_owner_object_id == object_id
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raise ThreadError, "already initialized"
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end
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@mon_mutex = Thread::Mutex.new
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@mon_mutex_owner_object_id = object_id
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@mon_owner = nil
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@mon_count = 0
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end
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def mon_check_owner
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if @mon_owner != Thread.current
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raise ThreadError, "current thread not owner"
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end
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end
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def mon_enter_for_cond(count)
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@mon_owner = Thread.current
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@mon_count = count
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end
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def mon_exit_for_cond
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count = @mon_count
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@mon_owner = nil
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@mon_count = 0
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return count
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end
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end
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# Use the Monitor class when you want to have a lock object for blocks with
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# mutual exclusion.
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#
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# require 'monitor'
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#
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# lock = Monitor.new
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# lock.synchronize do
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# # exclusive access
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# end
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#
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class Monitor
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include MonitorMixin
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alias try_enter try_mon_enter
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alias enter mon_enter
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alias exit mon_exit
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end
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# Documentation comments:
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# - All documentation comes from Nutshell.
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# - MonitorMixin.new_cond appears in the example, but is not documented in
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# Nutshell.
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# - All the internals (internal modules Accessible and Initializable, class
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# ConditionVariable) appear in RDoc. It might be good to hide them, by
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# making them private, or marking them :nodoc:, etc.
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# - RDoc doesn't recognise aliases, so we have mon_synchronize documented, but
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# not synchronize.
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# - mon_owner is in Nutshell, but appears as an accessor in a separate module
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# here, so is hard/impossible to RDoc. Some other useful accessors
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# (mon_count and some queue stuff) are also in this module, and don't appear
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# directly in the RDoc output.
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# - in short, it may be worth changing the code layout in this file to make the
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# documentation easier
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# Local variables:
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# mode: Ruby
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# tab-width: 8
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# End:
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