[NetworkChangeNotifier] Run Windows connection type computation on other thread

net/base/network_change_notifier_win.h

Index: net/base/network_change_notifier_win.h
diff --git a/net/base/network_change_notifier_win.h b/net/base/network_change_notifier_win.h
index 94bab7f8d100213744e72863ebb4a2b0aa6b51b8..61023240d2750bd1afde0847699cbb642d5aa020 100644
--- a/net/base/network_change_notifier_win.h
+++ b/net/base/network_change_notifier_win.h
@@ -9,8 +9,10 @@
 
 #include <memory>
 
+#include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/timer/timer.h"
@@ -18,6 +20,10 @@
 #include "net/base/net_export.h"
 #include "net/base/network_change_notifier.h"
 
+namespace base {
+class SingleThreadTaskRunner;
+}  // namespace base
+
 namespace net {
 
 // NetworkChangeNotifierWin inherits from NonThreadSafe, as all its internal
@@ -50,6 +56,7 @@ class NET_EXPORT_PRIVATE NetworkChangeNotifierWin
  private:
   class DnsConfigServiceThread;
   friend class NetworkChangeNotifierWinTest;
+  friend class TestNetworkChangeNotifierWin;
 
   // NetworkChangeNotifier methods:
   ConnectionType GetCurrentConnectionType() const override;
@@ -58,19 +65,16 @@ class NET_EXPORT_PRIVATE NetworkChangeNotifierWin
   // Must only be called on the thread |this| was created on.
   void OnObjectSignaled(HANDLE object) override;
 
-  // Does the actual work to determine the current connection type.
-  // It is not thread safe, see crbug.com/324913.
-  virtual ConnectionType RecomputeCurrentConnectionType() const;
-
   void SetCurrentConnectionType(ConnectionType connection_type);
 
   // Notifies IP address change observers of a change immediately, and notifies
   // network state change observers on a delay.  Must only be called on the
   // thread |this| was created on.
-  void NotifyObservers();
+  void NotifyObservers(ConnectionType connection_type);
 
   // Forwards connection type notifications to parent class.
   void NotifyParentOfConnectionTypeChange();
+  void NotifyParentOfConnectionTypeChangeImpl(ConnectionType connection_type);
 
   // Tries to start listening for a single subsequent address change.  Returns
   // false on failure.  The caller is responsible for updating |is_watching_|.
@@ -98,6 +102,7 @@ class NET_EXPORT_PRIVATE NetworkChangeNotifierWin
 
   // Thread on which we can run DnsConfigService.
   std::unique_ptr<DnsConfigServiceThread> dns_config_service_thread_;
+  scoped_refptr<base::SingleThreadTaskRunner> dns_task_runner_;

[pauljensen, 2017/05/22 18:01:51]

Hmm, can we avoid dns_task_runner_ and calculate_connection_type_ by instead
moving the DnsConfigServiceThread decl into this file, then having the test
reset dns_config_service_thread_ to be some overloaded impl in tests?

[jkarlin, 2017/05/23 11:44:38]

We could get rid of dns_task_runner_ that way I suppose, but injecting task
runners is pretty standard procedure and in this case seems pretty reasonable.

We could get rid of calculate_connection_type_ if we made it a virtual member
function of DnsConfigServiceThread and made DnsConfigServiceThread ref counted.
Would that be preferable? I'm not so sure as it changes the meaning of the
class.

[pauljensen, 2017/05/23 14:55:50]

Why would DnsConfigServiceThread need to be ref counted?  It's owned by NCNWin.

[jkarlin, 2017/05/23 15:11:06]

Ah, you're right. All tasks on the dns thread will finish running (thanks to the
call to Stop()) before the dns thread is destroyed, so it's safe. 

Can be done, but I don't see a strong reason to prefer that over what's in the
CL.

 
   mutable base::Lock last_computed_connection_type_lock_;
   ConnectionType last_computed_connection_type_;
@@ -108,6 +113,9 @@ class NET_EXPORT_PRIVATE NetworkChangeNotifierWin
   // Number of times polled to check if still offline.
   int offline_polls_;
 
+  // The callback run to calculate connection type.
+  base::Callback<ConnectionType()> calculate_connection_type_;
+
   // Used for calling WatchForAddressChange again on failure.
   base::WeakPtrFactory<NetworkChangeNotifierWin> weak_factory_;