Concurrency Utils

Monitor

Use the Monitor class when you want to have a lock object for blocks with mutual exclusion.

require 'monitor'

lock = Monitor.new
lock.synchronize do
  # exclusive access
end

Monitor Reference

MonitorMixin

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

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 buf.empty?. The producer thread (main thread) reads a line from ARGF and pushes it into buf then calls empty_cond.signal 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.

MonitorMixin Reference

Mutex_m

mutex_m.rb

When ‘mutex_m’ is required, any object that extends or includes Mutex_m will be treated like a Mutex.

Start by requiring the standard library Mutex_m:

require "mutex_m.rb"

From here you can extend an object with Mutex instance methods:

obj = Object.new
obj.extend Mutex_m

Or mixin Mutex_m into your module to your class inherit Mutex instance methods — remember to call super() in your class initialize method.

class Foo
  include Mutex_m
  def initialize
    # ...
    super()
  end
  # ...
end
obj = Foo.new
# this obj can be handled like Mutex

Mutex_m Reference

Sync

A class that provides two-phase lock with a counter. See Sync_m for details.

Sync Reference

Sync_m

A module that provides a two-phase lock with a counter.

Sync_m Reference

Synchronizer

A class that provides two-phase lock with a counter. See Sync_m for details.

Synchronizer Reference

Synchronizer_m

A module that provides a two-phase lock with a counter.

Synchronizer_m Reference