Add test demonstrating copying semaphore from parent to child.

spec/mach/semaphore_spec.rb

@@ -1,7 +1,5 @@
 require 'spec_helper'
-require 'mach/error'
-require 'mach/functions'
-require 'mach/semaphore'
+require 'mach'
 
 module Mach
   describe 'low level semaphore functions' do
@@ -30,5 +28,33 @@ module Mach
       sem.wait
       sem.destroy
     end
+
+    it 'coordinates access to shared resource between two tasks' do
+      sem = Semaphore.new(:value => 0)
+
+      port = Port.new
+      port.insert_right(:make_send)
+      Task.self.set_bootstrap_port(port)
+
+      child = fork do
+        parent_port = Task.self.get_bootstrap_port
+        Task.self.copy_send(parent_port)
+        # parent will copy send rights to sem into child task
+        sleep 0.5
+        sem.signal
+        Kernel.exit!
+      end
+
+      child_task_port = port.receive_right
+
+      start = Time.now.to_f
+      sem.insert_right(:copy_send, :ipc_space => child_task_port)
+      sem.wait
+      elapsed = Time.now.to_f - start
+
+      Process.wait child
+
+      elapsed.must be_gt(0.4)
+    end
   end
 end