Module: MonitorMixin (Ruby 2.2.4)
Description: Module : MonitorMixin - Ruby 2.2.4

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Support for the Ruby 2.2 series has ended. See here for reference.

### Home Classes Methods

### In Files

- monitor.rb

### Namespace

- CLASS MonitorMixin::ConditionVariable

### Methods

- ::extend_object
- ::new
- #mon_enter
- #mon_exit
- #mon_synchronize
- #mon_try_enter
- #new_cond
- #synchronize
- #try_mon_enter

### Class/Module Index

Quicksearch

- Monitor
- MonitorMixin
- MonitorMixin::ConditionVariable
- MonitorMixin::ConditionVariable::Timeout

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# 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.

### Public Class Methods

extend_object(obj) click to toggle source

                   # File monitor.rb, line 159
    def self.extend_object(obj)
      super(obj)
      obj.__send__(:mon_initialize)
    end

new(*args) click to toggle source

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

                   # File monitor.rb, line 231
    def initialize(*args)
      super
      mon_initialize
    end

### Public Instance Methods

mon_enter() click to toggle source

Enters exclusive section.

                   # File monitor.rb, line 183
    def mon_enter
      if @mon_owner != Thread.current
        @mon_mutex.lock
        @mon_owner = Thread.current
      end
      @mon_count += 1
    end

mon_exit() click to toggle source

Leaves exclusive section.

                   # File monitor.rb, line 194
    def mon_exit
      mon_check_owner
      @mon_count -=1
      if @mon_count == 0
        @mon_owner = nil
        @mon_mutex.unlock
      end
    end

mon_synchronize() click to toggle source

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

                   # File monitor.rb, line 208
    def mon_synchronize
      mon_enter
      begin
        yield
      ensure
        mon_exit
      end
    end

Also aliased as: synchronize
mon_try_enter() click to toggle source

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

                   # File monitor.rb, line 167
    def mon_try_enter
      if @mon_owner != Thread.current
        unless @mon_mutex.try_lock
          return false
        end
        @mon_owner = Thread.current
      end
      @mon_count += 1
      return true
    end

Also aliased as: try_mon_enter
new_cond() click to toggle source

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

                   # File monitor.rb, line 222
    def new_cond
      return ConditionVariable.new(self)
    end

synchronize() click to toggle source
Alias for: mon_synchronize
try_mon_enter() click to toggle source

For backward compatibility

Alias for: mon_try_enter