Mutex version of atomic reference.

Author: chrisseaton

lib/concurrent/atomic/atomic.rb

@@ -0,0 +1,52 @@
+module Concurrent
+
+  class MutexAtomic
+
+    def initialize(init = nil)
+      @value = init
+      @mutex = Mutex.new
+    end
+
+    def value
+      @mutex.lock
+      result = @value
+      @mutex.unlock
+
+      result
+    end
+
+    def value=(value)
+      @mutex.lock
+      result = @value = value
+      @mutex.unlock
+
+      result
+    end
+
+    def modify
+      @mutex.lock
+      result = yield @value
+      @value = result
+      @mutex.unlock
+
+      result
+    end
+
+    def compare_and_set(expect, update)
+      @mutex.lock
+      if @value == expect
+        @value = update
+        result = true
+      else
+        result = false
+      end
+      @mutex.unlock
+
+      result
+    end
+  end
+
+  class Atomic < MutexAtomic
+  end
+
+end

lib/concurrent/atomic/atomic_fixnum.rb

@@ -95,7 +95,6 @@ def decrement
     #
     #   @return [Boolean] true if the value was updated else false 
     def compare_and_set(expect, update)
-
       @mutex.lock
       if @value == expect
         @value = update

lib/concurrent/atomics.rb

@@ -1,3 +1,4 @@
+require 'concurrent/atomic/atomic'
 require 'concurrent/atomic/atomic_boolean'
 require 'concurrent/atomic/atomic_fixnum'
 require 'concurrent/atomic/condition'

spec/concurrent/atomic/atomic_spec.rb

@@ -0,0 +1,133 @@
+require 'spec_helper'
+
+share_examples_for :atomic do
+
+  context 'construction' do
+
+    it 'sets the initial value' do
+      described_class.new(:foo).value.should eq :foo
+    end
+
+    it 'defaults the initial value to nil' do
+      described_class.new.value.should eq nil
+    end
+  end
+
+  context '#value' do
+
+    it 'returns the current value' do
+      counter = described_class.new(:foo)
+      counter.value.should eq :foo
+    end
+  end
+
+  context '#value=' do
+
+    it 'sets the #value to the given object' do
+      atomic = described_class.new(:foo)
+      atomic.value = :bar
+      atomic.value.should eq :bar
+    end
+
+    it 'returns the new value' do
+      atomic = described_class.new(:foo)
+      (atomic.value = :bar).should eq :bar
+    end
+  end
+
+  context '#modify' do
+
+    it 'yields the current value' do
+      atomic = described_class.new(:foo)
+      current = []
+      atomic.modify { |value| current << value }
+      current.should eq [:foo]
+    end
+
+    it 'stores the value returned from the yield' do
+      atomic = described_class.new(:foo)
+      atomic.modify { |value| :bar }
+      atomic.value.should eq :bar
+    end
+
+    it 'returns the new value' do
+      atomic = described_class.new(:foo)
+      atomic.modify{ |value| :bar }.should eq :bar
+    end
+  end
+
+  context '#compare_and_set' do
+
+    it 'returns false if the value is not found' do
+      described_class.new(:foo).compare_and_set(:bar, :foo).should eq false
+    end
+
+    it 'returns true if the value is found' do
+      described_class.new(:foo).compare_and_set(:foo, :bar).should eq true
+    end
+
+    it 'sets if the value is found' do
+      f = described_class.new(:foo)
+      f.compare_and_set(:foo, :bar)
+      f.value.should eq :bar
+    end
+
+    it 'does not set if the value is not found' do
+      f = described_class.new(:foo)
+      f.compare_and_set(:bar, :baz)
+      f.value.should eq :foo
+    end
+  end
+end
+
+module Concurrent
+
+  describe MutexAtomic do
+
+    it_should_behave_like :atomic
+
+    specify 'construction is synchronized' do
+      mutex = double('mutex')
+      Mutex.should_receive(:new).once.with(no_args).and_return(mutex)
+      described_class.new
+    end
+
+    specify 'value is synchronized' do
+      mutex = double('mutex')
+      Mutex.stub(:new).with(no_args).and_return(mutex)
+      mutex.should_receive(:lock)
+      mutex.should_receive(:unlock)
+      described_class.new.value
+    end
+
+    specify 'value= is synchronized' do
+      mutex = double('mutex')
+      Mutex.stub(:new).with(no_args).and_return(mutex)
+      mutex.should_receive(:lock)
+      mutex.should_receive(:unlock)
+      described_class.new.value = 10
+    end
+
+    specify 'modify is synchronized' do
+      mutex = double('mutex')
+      Mutex.stub(:new).with(no_args).and_return(mutex)
+      mutex.should_receive(:lock)
+      mutex.should_receive(:unlock)
+      described_class.new(:foo).modify { |value| value }
+    end
+
+    specify 'compare_and_set is synchronized' do
+      mutex = double('mutex')
+      Mutex.stub(:new).with(no_args).and_return(mutex)
+      mutex.should_receive(:lock)
+      mutex.should_receive(:unlock)
+      described_class.new(14).compare_and_set(14, 2)
+    end
+  end
+
+  describe Atomic do
+    it 'inherits from MutexAtomic' do
+      Atomic.ancestors.should include(MutexAtomic)
+    end
+  end
+end