Bug 1710671: do SetAcceptLanguages during process preallocation to re…

…duce first-use overhead (especially for process-switch) r=dragana,necko-reviewers

Differential Revision: https://phabricator.services.mozilla.com/D114901

dom/ipc/ContentChild.cpp

@@ -118,6 +118,7 @@
 #include "nsBaseDragService.h"
 #include "nsDocShellLoadTypes.h"
 #include "nsFocusManager.h"
+#include "nsHttpHandler.h"
 #include "nsIConsoleService.h"
 #include "nsIInputStreamChannel.h"
 #include "nsILoadGroup.h"
@@ -2589,7 +2590,13 @@ mozilla::ipc::IPCResult ContentChild::RecvRemoteType(
 }
 
 // A method to initialize anything we need during the preallocation phase
-void ContentChild::PreallocInit() { EnsureNSSInitializedChromeOrContent(); }
+void ContentChild::PreallocInit() {
+  EnsureNSSInitializedChromeOrContent();
+
+  // SetAcceptLanguages() needs to read localized strings (file access),
+  // which is slow, so do this in prealloc
+  nsHttpHandler::PresetAcceptLanguages();
+}
 
 // Call RemoteTypePrefix() on the result to remove URIs if you want to use this
 // for telemetry.

netwerk/protocol/http/nsHttpHandler.cpp

@@ -1938,6 +1938,13 @@ static nsresult PrepareAcceptLanguages(const char* i_AcceptLanguages,
                                        &o_AcceptLanguages);
 }
 
+// Ensure that we've fetched the AcceptLanguages setting
+/* static */
+void nsHttpHandler::PresetAcceptLanguages() {
+  (void)GetInstance();
+  [[maybe_unused]] nsresult rv = gHttpHandler->SetAcceptLanguages();
+}
+
 nsresult nsHttpHandler::SetAcceptLanguages() {
   if (!NS_IsMainThread()) {
     nsCOMPtr<nsIThread> mainThread;

netwerk/protocol/http/nsHttpHandler.h

@@ -501,6 +501,10 @@ class nsHttpHandler final : public nsIHttpProtocolHandler,
 
   bool UseHTTPSRRForSpeculativeConnection() const;
 
+  // So we can ensure that this is done during process preallocation to
+  // avoid first-use overhead
+  static void PresetAcceptLanguages();
+
  private:
   nsHttpHandler();