Bug 1556911 - Don't instantiate NetworkConnectivityService off-main-thread r=dragana

This patch calls NetworkConnectivityService::GetSingleton() on the main thread
and keeps a ref to the service until shutdown.
Even though calling ncs->GetIPv6() off-main-thread is technically a data-race
in practice that's OK because only the simple decision whether to send
AAAA requests is made based on that value, which in itself is an optimization.
I filed bug 1556967 for making the connectivity service thread safe.

Differential Revision: https://phabricator.services.mozilla.com/D33765

--HG--
extra : moz-landing-system : lando

netwerk/base/NetworkConnectivityService.h

@@ -6,6 +6,9 @@
 #define NetworkConnectivityService_h_
 
 #include "nsINetworkConnectivityService.h"
+#include "nsIObserver.h"
+#include "nsIDNSListener.h"
+#include "nsIStreamListener.h"
 
 namespace mozilla {
 namespace net {

netwerk/dns/nsHostResolver.cpp

@@ -45,7 +45,6 @@
 #include "mozilla/DebugOnly.h"
 #include "mozilla/Preferences.h"
 #include "mozilla/StaticPrefs.h"
-#include "mozilla/net/NetworkConnectivityService.h"
 
 using namespace mozilla;
 using namespace mozilla::net;
@@ -599,6 +598,7 @@ nsresult nsHostResolver::Init() {
   LOG(("nsHostResolver::Init this=%p", this));
 
   mShutdown = false;
+  mNCS = NetworkConnectivityService::GetSingleton();
 
   // The preferences probably haven't been loaded from the disk yet, so we
   // need to register a callback that will set up the experiment once they
@@ -746,6 +746,8 @@ void nsHostResolver::Shutdown() {
     }
     // empty host database
     mRecordDB.Clear();
+
+    mNCS = nullptr;
   }
 
   ClearPendingQueue(pendingQHigh);
@@ -1241,15 +1243,12 @@ nsresult nsHostResolver::TrrLookup(nsHostRecord* aRec, TRR* pushedTRR) {
     }
     bool sendAgain;
 
-    RefPtr<NetworkConnectivityService> ncs =
-        NetworkConnectivityService::GetSingleton();
-
     do {
       sendAgain = false;
       if ((TRRTYPE_AAAA == rectype) && gTRRService &&
           (gTRRService->DisableIPv6() ||
-           (gTRRService->CheckIPv6Connectivity() &&
-            ncs->GetIPv6() == nsINetworkConnectivityService::NOT_AVAILABLE))) {
+           (gTRRService->CheckIPv6Connectivity() && mNCS &&
+            mNCS->GetIPv6() == nsINetworkConnectivityService::NOT_AVAILABLE))) {
         break;
       }
       LOG(("TRR Resolve %s type %d\n", addrRec->host.get(), (int)rectype));

netwerk/dns/nsHostResolver.h

@@ -24,6 +24,7 @@
 #include "mozilla/UniquePtr.h"
 #include "nsRefPtrHashtable.h"
 #include "nsIThreadPool.h"
+#include "mozilla/net/NetworkConnectivityService.h"
 
 class nsHostResolver;
 class nsResolveHostCallback;
@@ -552,6 +553,7 @@ class nsHostResolver : public nsISupports, public AHostResolver {
   mozilla::TimeDuration mShortIdleTimeout;
 
   RefPtr<nsIThreadPool> mResolverThreads;
+  RefPtr<mozilla::net::NetworkConnectivityService> mNCS;
 
   mozilla::Atomic<bool> mShutdown;
   mozilla::Atomic<uint32_t> mNumIdleTasks;