Added a wait with timeout to the platform semaphore class

src/platform-macos.cc

Index: src/platform-macos.cc
===================================================================
--- src/platform-macos.cc	(revision 1525)
+++ src/platform-macos.cc	(working copy)
@@ -565,6 +565,8 @@
   // platform is not needed here.
   void Wait() { semaphore_wait(semaphore_); }
 
+  bool Wait(int timeout);
+
   void Signal() { semaphore_signal(semaphore_); }
 
  private:
@@ -572,6 +574,14 @@
 };
 
 
+bool MacOSSemaphore::Wait(int timeout) {
+  mach_timespec_t ts;
+  ts.tv_sec = timeout / 1000000;
+  ts.tv_nsec = (timeout % 1000000) * 1000;
+  return semaphore_timedwait(semaphore_, ts) != KERN_OPERATION_TIMED_OUT;
+}
+
+
 Semaphore* OS::CreateSemaphore(int count) {
   return new MacOSSemaphore(count);
 }