Bug 1041906 Use AtomicReference for GeckoThread LaunchState. r=rnewman

mobile/android/base/GeckoThread.java

@@ -22,6 +22,7 @@ import android.util.Log;
 
 import java.io.IOException;
 import java.util.Locale;
+import java.util.concurrent.atomic.AtomicReference;
 
 public class GeckoThread extends Thread implements GeckoEventListener {
     private static final String LOGTAG = "GeckoThread";
@@ -34,9 +35,10 @@ public class GeckoThread extends Thread implements GeckoEventListener {
         GeckoRunning,
         GeckoExiting,
         GeckoExited
-    };
+    }
 
-    private static LaunchState sLaunchState = LaunchState.Launching;
+    private static AtomicReference<LaunchState> sLaunchState =
+                                            new AtomicReference<LaunchState>(LaunchState.Launching);
 
     private static GeckoThread sGeckoThread;
 
@@ -176,8 +178,6 @@ public class GeckoThread extends Thread implements GeckoEventListener {
         GeckoAppShell.runGecko(path, args, mUri, type);
     }
 
-    private static Object sLock = new Object();
-
     @Override
     public void handleMessage(String event, JSONObject message) {
         if ("Gecko:Ready".equals(event)) {
@@ -189,15 +189,11 @@ public class GeckoThread extends Thread implements GeckoEventListener {
 
     @RobocopTarget
     public static boolean checkLaunchState(LaunchState checkState) {
-        synchronized (sLock) {
-            return sLaunchState == checkState;
-        }
+        return sLaunchState.get() == checkState;
     }
 
     static void setLaunchState(LaunchState setState) {
-        synchronized (sLock) {
-            sLaunchState = setState;
-        }
+        sLaunchState.set(setState);
     }
 
     /**
@@ -205,11 +201,6 @@ public class GeckoThread extends Thread implements GeckoEventListener {
      * state is <code>checkState</code>; otherwise do nothing and return false.
      */
     static boolean checkAndSetLaunchState(LaunchState checkState, LaunchState setState) {
-        synchronized (sLock) {
-            if (sLaunchState != checkState)
-                return false;
-            sLaunchState = setState;
-            return true;
-        }
+        return sLaunchState.compareAndSet(checkState, setState);
     }
 }