ThreadLocalVar initial implementation.

Author: chrisseaton

lib/concurrent.rb

@@ -23,6 +23,7 @@
 require 'concurrent/scheduled_task'
 require 'concurrent/stoppable'
 require 'concurrent/supervisor'
+require 'concurrent/threadlocalvar'
 require 'concurrent/timer_task'
 require 'concurrent/utilities'
 

lib/concurrent/threadlocalvar.rb

@@ -0,0 +1,115 @@
+module Concurrent
+
+  module ThreadLocalSymbolAllocator
+
+    protected
+
+    def allocate_symbol
+      # Warning: this will space leak if you create ThreadLocalVars in a loop - not sure what to do about it
+      @symbol = "thread_local_symbol_#{self.object_id}_#{Time.now.hash}".to_sym
+    end
+
+  end
+
+  module ThreadLocalOldStorage
+
+    include ThreadLocalSymbolAllocator
+
+    protected
+
+    def allocate_storage
+      allocate_symbol
+    end
+
+    def get
+      Thread.current[@symbol]
+    end
+
+    def set(value)
+      Thread.current[@symbol] = value
+    end
+
+  end
+
+  module ThreadLocalNewStorage
+
+    include ThreadLocalSymbolAllocator
+
+    protected
+
+    def allocate_storage
+      allocate_symbol
+    end
+
+    def get
+      Thread.current.thread_variable_get(@symbol)
+    end
+
+    def set(value)
+      Thread.current.thread_variable_set(@symbol, value)
+    end
+
+  end
+
+  module ThreadLocalJavaStorage
+
+    protected
+
+    def allocate_storage
+      @var = java.lang.ThreadLocal.new
+    end
+
+    def get
+      @var.get
+    end
+
+    def set(value)
+      @var.set(value)
+    end
+
+  end
+
+  class ThreadLocalVar
+
+    NIL_SENTINEL = Object.new
+
+    if defined? java.lang.ThreadLocal.new
+      include ThreadLocalJavaStorage
+    elsif Thread.current.respond_to?(:thread_variable_set)
+      include ThreadLocalNewStorage
+    else
+      include ThreadLocalOldStorage
+    end
+
+    def initialize(default = nil)
+      @default = default
+      allocate_storage
+    end
+
+    def value
+      value = get
+
+      if value.nil?
+        @default
+      elsif value == NIL_SENTINEL
+        nil
+      else
+        value
+      end
+    end
+
+    def value=(value)
+      if value.nil?
+        stored_value = NIL_SENTINEL
+      else
+        stored_value = value
+      end
+
+      set stored_value
+
+      value
+    end
+
+  end
+
+end

spec/concurrent/threadlocalvar_spec.rb

@@ -0,0 +1,97 @@
+require 'spec_helper'
+
+module Concurrent
+
+  describe Future do
+
+    context '#initialize' do
+
+      it 'can set an initial value' do
+        v = ThreadLocalVar.new(14)
+        v.value.should eq 14
+      end
+
+      it 'sets nil as a default initial value' do
+        v = ThreadLocalVar.new
+        v.value.should be_nil
+      end
+
+      it 'sets the same initial value for all threads' do
+        v = ThreadLocalVar.new(14)
+        t1 = Thread.new { v.value }
+        t2 = Thread.new { v.value }
+        t1.value.should eq 14
+        t2.value.should eq 14
+      end
+
+    end
+
+    context '#value' do
+
+      it 'returns the current value' do
+        v = ThreadLocalVar.new(14)
+        v.value.should eq 14
+      end
+
+      it 'returns the value after modification' do
+        v = ThreadLocalVar.new(14)
+        v.value = 2
+        v.value.should eq 2
+      end
+
+    end
+
+    context '#value=' do
+
+      it 'sets a new value' do
+        v = ThreadLocalVar.new(14)
+        v.value = 2
+        v.value.should eq 2
+      end
+
+      it 'returns the new value' do
+        v = ThreadLocalVar.new(14)
+        (v.value = 2).should eq 2
+      end
+
+      it 'does not modify the initial value for other threads' do
+        v = ThreadLocalVar.new(14)
+        v.value = 2
+        t = Thread.new { v.value }
+        t.value.should eq 14
+      end
+
+      it 'does not modify the value for other threads' do
+        v = ThreadLocalVar.new(14)
+        v.value = 2
+
+        b1 = CountDownLatch.new(2)
+        b2 = CountDownLatch.new(2)
+
+        t1 = Thread.new do
+          b1.count_down
+          b1.wait
+          v.value = 1
+          b2.count_down
+          b2.wait
+          v.value
+        end
+        
+        t2 = Thread.new do
+          b1.count_down
+          b1.wait
+          v.value = 2
+          b2.count_down
+          b2.wait
+          v.value
+        end
+        
+        t1.value.should eq 1
+        t2.value.should eq 2
+      end
+
+    end
+
+  end
+
+end