MonitorMixin

Module

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.

Class Methods

extend_object(obj)
::
No documentation available

new(*args)
::

Use extend MonitorMixin or include MonitorMixin instead of this constructor. Have look at the examples above to understand how to use this module.

Instance Methods

mon_check_owner
#
No documentation available

mon_enter
#

Enters exclusive section.

mon_enter_for_cond(count)
#
No documentation available

mon_exit
#

Leaves exclusive section.

mon_exit_for_cond
#
No documentation available

mon_initialize
#

Initializes the MonitorMixin after being included in a class or when an object has been extended with the MonitorMixin

mon_synchronize() { || ... }
#

Enters exclusive section and executes the block. Leaves the exclusive section automatically when the block exits. See example under MonitorMixin.

mon_try_enter
#

Attempts to enter exclusive section. Returns false if lock fails.

new_cond
#

Creates a new MonitorMixin::ConditionVariable associated with the receiver.

synchronize
#
An alias for mon_synchronize

try_mon_enter
#
An alias for mon_try_enter