Merge pull request #40 from jdantonio/mvar-exchanger

Use MVars for exchanger instead of mutexes and conditions.

Author: mighe

lib/concurrent/exchanger.rb

@@ -1,54 +1,31 @@
 module Concurrent
   class Exchanger
 
-    def initialize
-      @mutex = Mutex.new
-      @condition = Condition.new
-      @slot = new_slot
+    EMPTY = Object.new
+
+    def initialize(opts = {})
+      @first = MVar.new(EMPTY, opts)
+      @second = MVar.new(MVar::EMPTY, opts)
     end
 
     def exchange(value, timeout = nil)
-      @mutex.synchronize do
-
-        replace_slot_if_fulfilled
-
-        slot = @slot
-
-        if slot.state == :empty
-          slot.value_1 = value
-          slot.state = :waiting
-          wait_for_value(slot, timeout)
-          slot.value_2
+      first = @first.take(timeout)
+      if first == MVar::TIMEOUT
+        nil
+      elsif first == EMPTY
+        @first.put value
+        second = @second.take timeout
+        if second == MVar::TIMEOUT
+          nil
         else
-          slot.value_2 = value
-          slot.state = :fulfilled
-          @condition.broadcast
-          slot.value_1
+          second
         end
-
+      else
+        @first.put EMPTY
+        @second.put value
+        first
       end
     end
 
-    Slot = Struct.new(:value_1, :value_2, :state)
-
-    private_constant :Slot
-
-    private
-
-    def replace_slot_if_fulfilled
-      @slot = new_slot if @slot.state == :fulfilled
-    end
-
-    def wait_for_value(slot, timeout)
-      remaining = Condition::Result.new(timeout)
-      while slot.state == :waiting && remaining.can_wait?
-        remaining = @condition.wait(@mutex, remaining.remaining_time)
-      end
-    end
-
-    def new_slot
-      Slot.new(nil, nil, :empty)
-    end
-
   end
-end
+end

spec/concurrent/exchanger_spec.rb

@@ -62,41 +62,5 @@ module Concurrent
         end
       end
     end
-
-    context 'spurious wake ups' do
-
-      before(:each) do
-        def subject.simulate_spurious_wake_up
-          @mutex.synchronize do
-            @condition.broadcast
-          end
-        end
-      end
-
-      it 'should resist to spurious wake ups without timeout' do
-        @expected = false
-        Thread.new { exchanger.exchange(1); @expected = true }
-
-        sleep(0.1)
-        subject.simulate_spurious_wake_up
-
-        sleep(0.1)
-        @expected.should be_false
-      end
-
-      it 'should resist to spurious wake ups with timeout' do
-        @expected = false
-        Thread.new { exchanger.exchange(1, 0.3); @expected = true }
-
-        sleep(0.1)
-        subject.simulate_spurious_wake_up
-
-        sleep(0.1)
-        @expected.should be_false
-
-        sleep(0.2)
-        @expected.should be_true
-      end
-    end
   end
 end