Merge pull request #203 from rocketraman/init-thread-safety

Made HystrixTimer initialization thread-safe

hystrix-core/src/main/java/com/netflix/hystrix/util/HystrixTimer.java

@@ -134,7 +134,7 @@ public void clear() {
      */
     protected void startThreadIfNeeded() {
         // create and start thread if one doesn't exist
-        if (executor.get() == null) {
+        while (executor.get() == null || ! executor.get().isInitialized()) {
             if (executor.compareAndSet(null, new ScheduledExecutor())) {
                 // initialize the executor that we 'won' setting
                 executor.get().initialize();
@@ -144,6 +144,7 @@ protected void startThreadIfNeeded() {
 
     private static class ScheduledExecutor {
         private volatile ScheduledThreadPoolExecutor executor;
+        private volatile boolean initialized;
 
         /**
          * We want this only done once when created in compareAndSet so use an initialize method
@@ -158,11 +159,16 @@ public Thread newThread(Runnable r) {
                 }
 
             });
+            initialized = true;
         }
 
         public ScheduledThreadPoolExecutor getThreadPool() {
             return executor;
         }
+
+        public boolean isInitialized() {
+            return initialized;
+        }
     }
 
     public static interface TimerListener {
@@ -390,4 +396,4 @@ public int getIntervalTimeInMilliseconds() {
 
         }
     }
-}
+}