Bug 1613873 - P3: Make nsDNSPrefetch support off main thread r=dragana

Differential Revision: https://phabricator.services.mozilla.com/D62918

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

netwerk/base/nsDNSPrefetch.cpp

@@ -12,25 +12,41 @@
 #include "nsIDNSService.h"
 #include "nsICancelable.h"
 #include "nsIURI.h"
+#include "mozilla/Atomics.h"
 #include "mozilla/Preferences.h"
 
 static nsIDNSService* sDNSService = nullptr;
-static bool sESNIEnabled = false;
+static mozilla::Atomic<bool, mozilla::Relaxed> sESNIEnabled(false);
+const char kESNIPref[] = "network.security.esni.enabled";
 
 nsresult nsDNSPrefetch::Initialize(nsIDNSService* aDNSService) {
+  MOZ_ASSERT(NS_IsMainThread());
+
   NS_IF_RELEASE(sDNSService);
   sDNSService = aDNSService;
   NS_IF_ADDREF(sDNSService);
-  mozilla::Preferences::AddBoolVarCache(&sESNIEnabled,
-                                        "network.security.esni.enabled");
+  mozilla::Preferences::RegisterCallback(nsDNSPrefetch::PrefChanged, kESNIPref);
+  PrefChanged(nullptr, nullptr);
   return NS_OK;
 }
 
 nsresult nsDNSPrefetch::Shutdown() {
   NS_IF_RELEASE(sDNSService);
+  mozilla::Preferences::UnregisterCallback(nsDNSPrefetch::PrefChanged,
+                                           kESNIPref);
   return NS_OK;
 }
 
+// static
+void nsDNSPrefetch::PrefChanged(const char* aPref, void* aClosure) {
+  if (!aPref || strcmp(aPref, kESNIPref) == 0) {
+    bool enabled = false;
+    if (NS_SUCCEEDED(mozilla::Preferences::GetBool(kESNIPref, &enabled))) {
+      sESNIEnabled = enabled;
+    }
+  }
+}
+
 nsDNSPrefetch::nsDNSPrefetch(nsIURI* aURI,
                              mozilla::OriginAttributes& aOriginAttributes,
                              nsIRequest::TRRMode aTRRMode,
@@ -44,12 +60,6 @@ nsDNSPrefetch::nsDNSPrefetch(nsIURI* aURI,
 }
 
 nsresult nsDNSPrefetch::Prefetch(uint32_t flags) {
-  // This can work properly only if this call is on the main thread.
-  // Curenlty we use nsDNSPrefetch only in nsHttpChannel which will call
-  // PrefetchHigh() from the main thread. Let's add assertion to catch
-  // if things change.
-  MOZ_ASSERT(NS_IsMainThread(), "Expecting DNS callback on main thread.");
-
   if (mHostname.IsEmpty()) return NS_ERROR_NOT_AVAILABLE;
 
   if (!sDNSService) return NS_ERROR_NOT_AVAILABLE;
@@ -61,12 +71,12 @@ nsresult nsDNSPrefetch::Prefetch(uint32_t flags) {
   // then our timing will be useless. However, in such a case,
   // mEndTimestamp will be a null timestamp and callers should check
   // TimingsValid() before using the timing.
-  nsCOMPtr<nsIEventTarget> main = mozilla::GetMainThreadEventTarget();
+  nsCOMPtr<nsIEventTarget> target = mozilla::GetCurrentThreadEventTarget();
 
   flags |= nsIDNSService::GetFlagsFromTRRMode(mTRRMode);
 
   nsresult rv = sDNSService->AsyncResolveNative(
-      mHostname, flags | nsIDNSService::RESOLVE_SPECULATE, this, main,
+      mHostname, flags | nsIDNSService::RESOLVE_SPECULATE, this, target,
       mOriginAttributes, getter_AddRefs(tmpOutstanding));
   if (NS_FAILED(rv)) {
     return rv;
@@ -79,8 +89,8 @@ nsresult nsDNSPrefetch::Prefetch(uint32_t flags) {
     esniHost.Append(mHostname);
     sDNSService->AsyncResolveByTypeNative(
         esniHost, nsIDNSService::RESOLVE_TYPE_TXT,
-        flags | nsIDNSService::RESOLVE_SPECULATE, this, main, mOriginAttributes,
-        getter_AddRefs(tmpOutstanding));
+        flags | nsIDNSService::RESOLVE_SPECULATE, this, target,
+        mOriginAttributes, getter_AddRefs(tmpOutstanding));
   }
   return NS_OK;
 }
@@ -104,8 +114,6 @@ NS_IMPL_ISUPPORTS(nsDNSPrefetch, nsIDNSListener)
 NS_IMETHODIMP
 nsDNSPrefetch::OnLookupComplete(nsICancelable* request, nsIDNSRecord* rec,
                                 nsresult status) {
-  MOZ_ASSERT(NS_IsMainThread(), "Expecting DNS callback on main thread.");
-
   if (mStoreTiming) {
     mEndTimestamp = mozilla::TimeStamp::Now();
   }
@@ -113,6 +121,10 @@ nsDNSPrefetch::OnLookupComplete(nsICancelable* request, nsIDNSRecord* rec,
   if (listener) {
     listener->OnLookupComplete(request, rec, status);
   }
+  // OnLookupComplete should be called on the target thread, so we release
+  // mListener here to make sure mListener is also released on the target
+  // thread.
+  mListener = nullptr;
   return NS_OK;
 }
 
@@ -120,8 +132,6 @@ NS_IMETHODIMP
 nsDNSPrefetch::OnLookupByTypeComplete(nsICancelable* request,
                                       nsIDNSByTypeRecord* res,
                                       nsresult status) {
-  MOZ_ASSERT(NS_IsMainThread(), "Expecting DNS callback on main thread.");
-
   if (mStoreTiming) {
     mEndTimestamp = mozilla::TimeStamp::Now();
   }
@@ -129,5 +139,9 @@ nsDNSPrefetch::OnLookupByTypeComplete(nsICancelable* request,
   if (listener) {
     listener->OnLookupByTypeComplete(request, res, status);
   }
+  // OnLookupByTypeComplete should be called on the target thread, so we release
+  // mListener here to make sure mListener is also released on the target
+  // thread.
+  mListener = nullptr;
   return NS_OK;
 }

netwerk/base/nsDNSPrefetch.h

@@ -43,6 +43,8 @@ class nsDNSPrefetch final : public nsIDNSListener {
   nsresult PrefetchMedium(bool refreshDNS = false);
   nsresult PrefetchLow(bool refreshDNS = false);
 
+  static void PrefChanged(const char* aPref, void* aClosure);
+
  private:
   nsCString mHostname;
   bool mIsHttps;