# frozen_string_literal: false
# 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
# You can read more about the general principles on the Wikipedia page for
# Monitors[http://en.wikipedia.org/wiki/Monitor_%28synchronization%29]
# === Simple object.extend
# buf.extend(MonitorMixin)
# empty_cond = buf.new_cond
# empty_cond.wait_while { buf.empty? }
# 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
# class SynchronizedArray < Array
# alias :old_shift :shift
# alias :old_unshift :unshift
# +SynchronizedArray+ implements an Array with synchronized access to items.
# This Class is implemented as subclass of Array which includes the
EXCEPTION_NEVER = {Exception => :never}.freeze
EXCEPTION_IMMEDIATE = {Exception => :immediate}.freeze
# 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.
class Timeout < Exception; end
# Releases the lock held in the associated monitor and waits; reacquires the lock on wakeup.
# If +timeout+ is given, this method returns after +timeout+ seconds passed,
# even if no other thread doesn't signal.
Thread.handle_interrupt(EXCEPTION_NEVER) do
@monitor.__send__(:mon_check_owner)
count = @monitor.__send__(:mon_exit_for_cond)
Thread.handle_interrupt(EXCEPTION_IMMEDIATE) do
@cond.wait(@monitor.instance_variable_get(:@mon_mutex), timeout)
@monitor.__send__(:mon_enter_for_cond, count)
# Calls wait repeatedly while the given block yields a truthy value.
# Calls wait repeatedly until the given block yields a truthy value.
# Wakes up the first thread in line waiting for this lock.
@monitor.__send__(:mon_check_owner)
# Wakes up all threads waiting for this lock.
@monitor.__send__(:mon_check_owner)
@cond = Thread::ConditionVariable.new
def self.extend_object(obj)
obj.__send__(:mon_initialize)
# Attempts to enter exclusive section. Returns +false+ if lock fails.
if @mon_owner != Thread.current
unless @mon_mutex.try_lock
@mon_owner = Thread.current
# For backward compatibility
alias try_mon_enter mon_try_enter
# Enters exclusive section.
if @mon_owner != Thread.current
@mon_owner = Thread.current
# Leaves exclusive section.
# Returns true if this monitor is locked by any thread
# Returns true if this monitor is locked by current thread.
@mon_mutex.locked? && @mon_owner == Thread.current
# Enters exclusive section and executes the block. Leaves the exclusive
# section automatically when the block exits. See example under
# Prevent interrupt on handling interrupts; for example timeout errors
# it may break locking state.
Thread.handle_interrupt(Exception => :never){ mon_enter }
Thread.handle_interrupt(EXCEPTION_NEVER){ mon_exit }
alias synchronize mon_synchronize
# Creates a new MonitorMixin::ConditionVariable associated with the
return ConditionVariable.new(self)
# Use <tt>extend MonitorMixin</tt> or <tt>include MonitorMixin</tt> instead
# of this constructor. Have look at the examples above to understand how to
# Initializes the MonitorMixin after being included in a class or when an
# object has been extended with the MonitorMixin
@mon_mutex = Thread::Mutex.new
if @mon_owner != Thread.current
raise ThreadError, "current thread not owner"
def mon_enter_for_cond(count)
@mon_owner = Thread.current
# Use the Monitor class when you want to have a lock object for blocks with
alias try_enter try_mon_enter
# Documentation comments:
# - All documentation comes from Nutshell.
# - MonitorMixin.new_cond appears in the example, but is not documented in
# - 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
# - 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
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