Bug 1646776 - Move the preloader for stylesheets to SheetLoadData rather than StreamLoader. r=mayhemer

So as to make sense in a world where we can coalesce loads across
documents. The per-load object is the SheetLoadData, so this way we
guarantee that we fire the right events in presence of the load
coalescing that the SharedStyleSheetCache does.

Differential Revision: https://phabricator.services.mozilla.com/D80380

layout/style/Loader.cpp

@@ -21,6 +21,7 @@
 #include "mozilla/SchedulerGroup.h"
 #include "mozilla/URLPreloader.h"
 #include "nsIRunnable.h"
+#include "nsISupportsPriority.h"
 #include "nsITimedChannel.h"
 #include "nsICachingChannel.h"
 #include "nsSyncLoadService.h"
@@ -412,6 +413,14 @@ SheetLoadData::AfterProcessNextEvent(nsIThreadInternal* aThread,
   return NS_OK;
 }
 
+void SheetLoadData::PrioritizeAsPreload(nsIChannel* aChannel) {
+  if (nsCOMPtr<nsISupportsPriority> sp = do_QueryInterface(aChannel)) {
+    sp->AdjustPriority(nsISupportsPriority::PRIORITY_HIGHEST);
+  }
+}
+
+void SheetLoadData::PrioritizeAsPreload() { PrioritizeAsPreload(Channel()); }
+
 void SheetLoadData::FireLoadEvent(nsIThreadInternal* aThread) {
   // First remove ourselves as a thread observer.  But we need to keep
   // ourselves alive while doing that!
@@ -1239,6 +1248,9 @@ nsresult Loader::LoadSheet(SheetLoadData& aLoadData, SheetState aSheetState) {
 
   SheetLoadDataHashKey key(aLoadData);
   mLoadsPerformed.PutEntry(key);
+
+  auto preloadKey = PreloadHashKey::CreateAsStyle(aLoadData);
+  bool coalescedLoad = false;
   if (mSheets) {
     // If we have at least one other load ongoing, then we can defer it until
     // all non-pending loads are done.
@@ -1249,17 +1261,23 @@ nsresult Loader::LoadSheet(SheetLoadData& aLoadData, SheetState aSheetState) {
       mSheets->DeferSheetLoad(aLoadData);
       return NS_OK;
     }
-    if (mSheets->CoalesceLoad(key, aLoadData, aSheetState)) {
+
+    if ((coalescedLoad = mSheets->CoalesceLoad(key, aLoadData, aSheetState))) {
       if (aSheetState == SheetState::Pending) {
         ++mPendingLoadCount;
+        return NS_OK;
       }
-
-      // All done here; once the load completes we'll be marked complete
-      // automatically
-      return NS_OK;
     }
   }
 
+  aLoadData.NotifyOpen(preloadKey, mDocument,
+                       aLoadData.mIsPreload == IsPreload::FromLink);
+  if (coalescedLoad) {
+    // All done here; once the load completes we'll be marked complete
+    // automatically.
+    return NS_OK;
+  }
+
   nsCOMPtr<nsILoadGroup> loadGroup;
   nsCOMPtr<nsICookieJarSettings> cookieJarSettings;
   if (mDocument) {
@@ -1339,8 +1357,8 @@ nsresult Loader::LoadSheet(SheetLoadData& aLoadData, SheetState aSheetState) {
       cos->AddClassFlags(nsIClassOfService::Leader);
     }
     if (aLoadData.mIsPreload == IsPreload::FromLink) {
-      StreamLoader::PrioritizeAsPreload(channel);
-      StreamLoader::AddLoadBackgroundFlag(channel);
+      SheetLoadData::PrioritizeAsPreload(channel);
+      SheetLoadData::AddLoadBackgroundFlag(channel);
     }
   }
 
@@ -1414,16 +1432,12 @@ nsresult Loader::LoadSheet(SheetLoadData& aLoadData, SheetState aSheetState) {
                         nsINetworkPredictor::LEARN_LOAD_SUBRESOURCE, mDocument);
   }
 
-  auto preloadKey = PreloadHashKey::CreateAsStyle(aLoadData);
-  streamLoader->NotifyOpen(preloadKey, channel, mDocument,
-                           aLoadData.mIsPreload == IsPreload::FromLink);
-
   rv = channel->AsyncOpen(streamLoader);
   if (NS_FAILED(rv)) {
     LOG_ERROR(("  Failed to create stream loader"));
-    // ChannelOpenFailed makes sure that <link preload> nodes will get the
-    // proper notification about not being able to load this resource.
     streamLoader->ChannelOpenFailed(rv);
+    // NOTE: NotifyStop will be done in SheetComplete -> NotifyObservers.
+    aLoadData.NotifyStart(channel);
     SheetComplete(aLoadData, rv);
     return rv;
   }
@@ -1497,6 +1511,7 @@ void Loader::NotifyObservers(SheetLoadData& aData, nsresult aStatus) {
   if (aData.mURI) {
     MOZ_DIAGNOSTIC_ASSERT(mOngoingLoadCount);
     --mOngoingLoadCount;
+    aData.NotifyStop(aStatus);
   }
 
   if (aData.mMustNotify) {

layout/style/SheetLoadData.h

@@ -10,6 +10,7 @@
 #include "mozilla/css/Loader.h"
 #include "mozilla/css/SheetParsingMode.h"
 #include "mozilla/Encoding.h"
+#include "mozilla/PreloaderBase.h"
 #include "mozilla/NotNull.h"
 #include "mozilla/UniquePtr.h"
 #include "nsIThreadInternal.h"
@@ -37,7 +38,9 @@ static_assert(eAuthorSheetFeatures == 0 && eUserSheetFeatures == 1 &&
               "sheet parsing mode constants won't fit "
               "in SheetLoadData::mParsingMode");
 
-class SheetLoadData final : public nsIRunnable, public nsIThreadObserver {
+class SheetLoadData final : public PreloaderBase,
+                            public nsIRunnable,
+                            public nsIThreadObserver {
   using MediaMatched = dom::LinkStyle::MediaMatched;
   using IsAlternate = dom::LinkStyle::IsAlternate;
   using IsPreload = Loader::IsPreload;
@@ -47,6 +50,10 @@ class SheetLoadData final : public nsIRunnable, public nsIThreadObserver {
   virtual ~SheetLoadData();
 
  public:
+  // PreloaderBase
+  static void PrioritizeAsPreload(nsIChannel* aChannel);
+  void PrioritizeAsPreload() final;
+
   // Data for loading a sheet linked from a document
   SheetLoadData(Loader* aLoader, const nsAString& aTitle, nsIURI* aURI,
                 StyleSheet* aSheet, bool aSyncLoad, nsINode* aOwningNode,

layout/style/StreamLoader.cpp

@@ -11,7 +11,6 @@
 #include "nsContentUtils.h"
 #include "nsIChannel.h"
 #include "nsIInputStream.h"
-#include "nsISupportsPriority.h"
 
 #include <limits>
 
@@ -31,19 +30,11 @@ StreamLoader::~StreamLoader() {
 
 NS_IMPL_ISUPPORTS(StreamLoader, nsIStreamListener)
 
-// static
-void StreamLoader::PrioritizeAsPreload(nsIChannel* aChannel) {
-  if (nsCOMPtr<nsISupportsPriority> sp = do_QueryInterface(aChannel)) {
-    sp->AdjustPriority(nsISupportsPriority::PRIORITY_HIGHEST);
-  }
-}
-
-void StreamLoader::PrioritizeAsPreload() { PrioritizeAsPreload(Channel()); }
-
 /* nsIRequestObserver implementation */
 NS_IMETHODIMP
 StreamLoader::OnStartRequest(nsIRequest* aRequest) {
-  NotifyStart(aRequest);
+  MOZ_ASSERT(aRequest);
+  mSheetLoadData->NotifyStart(aRequest);
 
   // It's kinda bad to let Web content send a number that results
   // in a potentially large allocation directly, but efficiency of
@@ -72,8 +63,6 @@ StreamLoader::OnStopRequest(nsIRequest* aRequest, nsresult aStatus) {
 #endif
 
   nsresult rv = mStatus;
-  auto notifyStop = MakeScopeExit([&] { NotifyStop(aRequest, rv); });
-
   // Decoded data
   nsCString utf8String;
   {
@@ -93,11 +82,6 @@ StreamLoader::OnStopRequest(nsIRequest* aRequest, nsresult aStatus) {
     rv = mSheetLoadData->VerifySheetReadyToParse(aStatus, mBOMBytes, bytes,
                                                  channel);
     if (rv != NS_OK_PARSE_SHEET) {
-      // VerifySheetReadyToParse returns `NS_OK` when there was something wrong
-      // with the script.  We need to override the result so that any <link
-      // preload> tags associted to this load will be notified the "error"
-      // event.  It's fine because this error goes no where.
-      rv = NS_ERROR_NOT_AVAILABLE;
       return rv;
     }
 

layout/style/StreamLoader.h

@@ -11,31 +11,24 @@
 #include "nsString.h"
 #include "mozilla/css/SheetLoadData.h"
 #include "mozilla/Assertions.h"
-#include "mozilla/PreloaderBase.h"
 
 class nsIInputStream;
 
 namespace mozilla {
 namespace css {
 
-class StreamLoader : public PreloaderBase, public nsIStreamListener {
+class StreamLoader : public nsIStreamListener {
  public:
   NS_DECL_ISUPPORTS
   NS_DECL_NSIREQUESTOBSERVER
   NS_DECL_NSISTREAMLISTENER
 
-  // PreloaderBase
-  static void PrioritizeAsPreload(nsIChannel* aChannel);
-  virtual void PrioritizeAsPreload() override;
-
   explicit StreamLoader(SheetLoadData&);
 
   void ChannelOpenFailed(nsresult rv) {
 #ifdef NIGHTLY_BUILD
     mChannelOpenFailed = true;
 #endif
-    NotifyStart(Channel());
-    NotifyStop(Channel(), rv);
   }
 
  private: