Fix race condition in NetworkChangeNotifier on Android.

net/android/network_change_notifier_android.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/android/network_change_notifier_android.h"
 
+#include "base/android/jni_android.h"
 #include "base/logging.h"
-#include "base/android/jni_android.h"
 #include "jni/NetworkChangeNotifier_jni.h"
 
 namespace net {
 namespace android {
 
-NetworkChangeNotifier::NetworkChangeNotifier() {
-  JNIEnv* env = base::android::AttachCurrentThread();
-  CreateJavaObject(env);
+namespace {
+
+// Returns whether the provided connection type is known.
+bool CheckConnectionType(int connection_type) {
+  switch (connection_type) {
+    case NetworkChangeNotifier::CONNECTION_UNKNOWN:
+    case NetworkChangeNotifier::CONNECTION_ETHERNET:
+    case NetworkChangeNotifier::CONNECTION_WIFI:
+    case NetworkChangeNotifier::CONNECTION_2G:
+    case NetworkChangeNotifier::CONNECTION_3G:
+    case NetworkChangeNotifier::CONNECTION_4G:
+    case NetworkChangeNotifier::CONNECTION_NONE:
+      return true;
+    default:
+      NOTREACHED() << "Unknown connection type received: " << connection_type;
+      return false;
+  }
 }
 
+}  // namespace
+
 NetworkChangeNotifier::~NetworkChangeNotifier() {
   JNIEnv* env = base::android::AttachCurrentThread();
   Java_NetworkChangeNotifier_destroy(
       env, java_network_change_notifier_.obj());
 }
 
+void NetworkChangeNotifier::NotifyObservers(
+    JNIEnv* env, jobject obj, jint new_connection_type) {
+  base::subtle::Release_Store(
+      &connection_type_,
+      CheckConnectionType(new_connection_type) ?

[szym, 2012/09/14 18:25:23]

Do this jint -> int and jint -> AtomicWord implicit conversions work? I recall
there was some reason for the explicit switch statement in
GetCurrentConnectionType.

nit: Create a new temporary variable (e.g., |known_connection_type|) to make it
more readable.

+          new_connection_type : CONNECTION_UNKNOWN);
+  NotifyObserversOfConnectionTypeChange();
+}
+
+jint NetworkChangeNotifier::GetConnectionType(JNIEnv* env, jobject obj) {
+  return GetCurrentConnectionType();
+}
+
+// static
+bool NetworkChangeNotifier::Register(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+NetworkChangeNotifier::NetworkChangeNotifier() {
+  JNIEnv* env = base::android::AttachCurrentThread();
+  base::subtle::Release_Store(&connection_type_, CONNECTION_UNKNOWN);
+  CreateJavaObject(env);
+}
+
 void NetworkChangeNotifier::CreateJavaObject(JNIEnv* env) {
   java_network_change_notifier_.Reset(
       Java_NetworkChangeNotifier_create(
           env,
           base::android::GetApplicationContext(),
           reinterpret_cast<jint>(this)));
 }
 
-void NetworkChangeNotifier::NotifyObservers(JNIEnv* env, jobject obj) {
-  NotifyObserversOfConnectionTypeChange();
-}
-
 net::NetworkChangeNotifier::ConnectionType
     NetworkChangeNotifier::GetCurrentConnectionType() const {
-  JNIEnv* env = base::android::AttachCurrentThread();
-
-  // Pull the connection type from the Java-side then convert it to a
-  // native-side NetworkChangeNotifier::ConnectionType.
-  jint connection_type = Java_NetworkChangeNotifier_connectionType(
-      env, java_network_change_notifier_.obj());
-  switch (connection_type) {
-    case CONNECTION_UNKNOWN:
-      return CONNECTION_UNKNOWN;
-    case CONNECTION_ETHERNET:
-      return CONNECTION_ETHERNET;
-    case CONNECTION_WIFI:
-      return CONNECTION_WIFI;
-    case CONNECTION_2G:
-      return CONNECTION_2G;
-    case CONNECTION_3G:
-      return CONNECTION_3G;
-    case CONNECTION_4G:
-      return CONNECTION_4G;
-    case CONNECTION_NONE:
-      return CONNECTION_NONE;
-    default:
-      NOTREACHED() << "Unknown connection type received: " << connection_type;
-      return CONNECTION_NONE;
-  }
-}
-
-// static
-bool NetworkChangeNotifier::Register(JNIEnv* env) {
-  return RegisterNativesImpl(env);
+  return static_cast<net::NetworkChangeNotifier::ConnectionType>(
+      base::subtle::Acquire_Load(&connection_type_));
 }
 
 }  // namespace android
 }  // namespace net