promise.rb in thread-0.0.4.2

- old
+ new

@@ -13,11 +13,10 @@
 # A promise is an object that lets you wait for a value to be delivered to it.
 class Thread::Promise
 	# Create a promise.
 	def initialize
 		@mutex = Mutex.new
-		@cond  = ConditionVariable.new
 	end
 
 	# Check if a value has been delivered.
 	def delivered?
 		@mutex.synchronize {
@@ -31,30 +30,43 @@
 	def deliver (value)
 		return if delivered?
 
 		@mutex.synchronize {
 			@value = value
-			@cond.broadcast
+
+			cond.broadcast if cond?
 		}
 
 		self
 	end
 
 	alias << deliver
 
 	# Get the value that's been delivered, if none has been delivered yet the call
 	# will block until one is delivered.
+	#
+	# An optional timeout can be passed which will return nil if nothing has been
+	# delivered.
 	def value (timeout = nil)
 		return @value if delivered?
 
 		@mutex.synchronize {
-			@cond.wait(@mutex, *timeout)
+			cond.wait(@mutex, *timeout)
 		}
 
 		return @value if delivered?
 	end
 
 	alias ~ value
+
+private
+	def cond?
+		instance_variable_defined? :@cond
+	end
+
+	def cond
+		@cond ||= ConditionVariable.new
+	end
 end
 
 module Kernel
 	def promise
 		Thread::Promise.new