[Cronet] Fix race with NetLogWithNetworkChangeEvents registration with NCN

components/cronet/android/cronet_url_request_context_adapter.cc

 // Copyright 2014 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 "components/cronet/android/cronet_url_request_context_adapter.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 46 matching lines @@
 
 #if defined(DATA_REDUCTION_PROXY_SUPPORT)
 #include "components/cronet/android/cronet_data_reduction_proxy.h"
 #endif
 
 namespace {
 
 // This class wraps a NetLog that also contains network change events.
 class NetLogWithNetworkChangeEvents {
  public:
-  NetLogWithNetworkChangeEvents() : net_log_(), net_change_logger_(&net_log_) {}
+  NetLogWithNetworkChangeEvents() {}
 
   net::NetLog* net_log() { return &net_log_; }
+  // This function registers with the NetworkChangeNotifier and so must be
+  // called *after* the NetworkChangeNotifier is created. Should only be
+  // called on the UI thread as it is not thread-safe and the UI thread is
+  // the thread the NetworkChangeNotifier is created on. This function is
+  // not thread-safe because accesses to |net_change_logger_| are not atomic.
+  // There might be multiple CronetEngines each with a network thread so
+  // so the UI thread is used. |g_net_log_| also outlives the network threads
+  // so it would be unsafe to receive callbacks on the network threads without
+  // a complicated thread-safe reference-counting system to control callback
+  // registration.
+  void EnsureInitializedOnMainThread() {
+    DCHECK(base::MessageLoopForUI::IsCurrent());
+    if (net_change_logger_)
+      return;
+    net_change_logger_.reset(new net::LoggingNetworkChangeObserver(&net_log_));
+  }
 
  private:
   net::NetLog net_log_;
   // LoggingNetworkChangeObserver logs network change events to a NetLog.
   // This class bundles one LoggingNetworkChangeObserver with one NetLog,
   // so network change event are logged just once in the NetLog.
-  net::LoggingNetworkChangeObserver net_change_logger_;
+  std::unique_ptr<net::LoggingNetworkChangeObserver> net_change_logger_;
 
   DISALLOW_COPY_AND_ASSIGN(NetLogWithNetworkChangeEvents);
 };
 
 // Use a global NetLog instance. See crbug.com/486120.
 static base::LazyInstance<NetLogWithNetworkChangeEvents>::Leaky g_net_log =
     LAZY_INSTANCE_INITIALIZER;
 
 const char kHttpServerProperties[] = "net.http_server_properties";
 // Current version of disk storage.
@@ skipping 319 matching lines @@
   jcaller_ref.Reset(env, jcaller);
   proxy_config_service_ = net::ProxyService::CreateSystemProxyConfigService(
       GetNetworkTaskRunner(), nullptr /* Ignored on Android */);
   net::ProxyConfigServiceAndroid* android_proxy_config_service =
       static_cast<net::ProxyConfigServiceAndroid*>(proxy_config_service_.get());
   // If a PAC URL is present, ignore it and use the address and port of
   // Android system's local HTTP proxy server. See: crbug.com/432539.
   // TODO(csharrison) Architect the wrapper better so we don't need to cast for
   // android ProxyConfigServices.
   android_proxy_config_service->set_exclude_pac_url(true);
+  g_net_log.Get().EnsureInitializedOnMainThread();
   GetNetworkTaskRunner()->PostTask(
       FROM_HERE,
       base::Bind(&CronetURLRequestContextAdapter::InitializeOnNetworkThread,
                  base::Unretained(this), base::Passed(&context_config_),
                  jcaller_ref));
 }
 
 void CronetURLRequestContextAdapter::
     EnableNetworkQualityEstimatorOnNetworkThread(bool use_local_host_requests,
                                                  bool use_smaller_responses) {
@@ skipping 478 matching lines @@
     JNIEnv* env,
     const JavaParamRef<jclass>& jcaller) {
   base::StatisticsRecorder::Initialize();
   std::vector<uint8_t> data;
   if (!HistogramManager::GetInstance()->GetDeltas(&data))
     return ScopedJavaLocalRef<jbyteArray>();
   return base::android::ToJavaByteArray(env, &data[0], data.size());
 }
 
 }  // namespace cronet