Bug 1456626, use dedicated background thread for nsJARChannel::asyncOpen to avoid blocking r=valentin,michal,froydnj

Differential Revision: https://phabricator.services.mozilla.com/D73065

modules/libjar/nsJARChannel.cpp

@@ -200,11 +200,6 @@ nsresult nsJARChannel::Init(nsIURI* uri) {
   LOG(("nsJARChannel::Init [this=%p]\n", this));
   nsresult rv;
 
-  mWorker = do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID, &rv);
-  if (NS_FAILED(rv)) {
-    return rv;
-  }
-
   mJarURI = do_QueryInterface(uri, &rv);
   if (NS_FAILED(rv)) return rv;
 
@@ -370,7 +365,6 @@ nsresult nsJARChannel::OpenLocalFile() {
 
   MOZ_ASSERT(NS_IsMainThread());
 
-  MOZ_ASSERT(mWorker);
   MOZ_ASSERT(mIsPending);
   MOZ_ASSERT(mJarFile);
 
@@ -409,31 +403,34 @@ nsresult nsJARChannel::OpenLocalFile() {
   nsAutoCString innerJarEntry(mInnerJarEntry);
 
   RefPtr<nsJARChannel> self = this;
-  return mWorker->Dispatch(NS_NewRunnableFunction(
-      "nsJARChannel::OpenLocalFile", [self, jarCache, clonedFile, localJARURI,
-                                      jarEntry, innerJarEntry]() mutable {
-        RefPtr<nsJARInputThunk> input;
-        nsresult rv =
-            CreateLocalJarInput(jarCache, clonedFile, innerJarEntry,
-                                localJARURI, jarEntry, getter_AddRefs(input));
+  return NS_DispatchBackgroundTask(
+      NS_NewRunnableFunction(
+          "nsJARChannel::OpenLocalFile",
+          [self, jarCache, clonedFile, localJARURI, jarEntry,
+           innerJarEntry]() mutable {
+            RefPtr<nsJARInputThunk> input;
+            nsresult rv = CreateLocalJarInput(jarCache, clonedFile,
+                                              innerJarEntry, localJARURI,
+                                              jarEntry, getter_AddRefs(input));
 
-        nsCOMPtr<nsIRunnable> target;
-        if (NS_SUCCEEDED(rv)) {
-          target = NewRunnableMethod<RefPtr<nsJARInputThunk>, bool>(
-              "nsJARChannel::ContinueOpenLocalFile", self,
-              &nsJARChannel::ContinueOpenLocalFile, input, false);
-        } else {
-          target = NewRunnableMethod<nsresult, bool>(
-              "nsJARChannel::OnOpenLocalFileComplete", self,
-              &nsJARChannel::OnOpenLocalFileComplete, rv, false);
-        }
+            nsCOMPtr<nsIRunnable> target;
+            if (NS_SUCCEEDED(rv)) {
+              target = NewRunnableMethod<RefPtr<nsJARInputThunk>, bool>(
+                  "nsJARChannel::ContinueOpenLocalFile", self,
+                  &nsJARChannel::ContinueOpenLocalFile, input, false);
+            } else {
+              target = NewRunnableMethod<nsresult, bool>(
+                  "nsJARChannel::OnOpenLocalFileComplete", self,
+                  &nsJARChannel::OnOpenLocalFileComplete, rv, false);
+            }
 
-        // nsJARChannel must be release on main thread, and sometimes
-        // this still hold nsJARChannel after dispatched.
-        self = nullptr;
+            // nsJARChannel must be release on main thread, and sometimes
+            // this still hold nsJARChannel after dispatched.
+            self = nullptr;
 
-        NS_DispatchToMainThread(target.forget());
-      }));
+            NS_DispatchToMainThread(target.forget());
+          }),
+      NS_DISPATCH_EVENT_MAY_BLOCK);
 }
 
 nsresult nsJARChannel::ContinueOpenLocalFile(nsJARInputThunk* aInput,

modules/libjar/nsJARChannel.h

@@ -104,9 +104,6 @@ class nsJARChannel final : public nsIJARChannel,
   nsCOMPtr<nsIURI> mJarBaseURI;
   nsCString mJarEntry;
   nsCString mInnerJarEntry;
-
-  // use StreamTransportService as background thread
-  nsCOMPtr<nsIEventTarget> mWorker;
 };
 
 #endif  // nsJARChannel_h__