Bug 1724101 - Protect nsHtml5StreamListener::mDelegate with a monitor. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D122471

parser/html/moz.build

@@ -38,6 +38,7 @@ EXPORTS += [
     "nsHtml5StreamListener.h",
     "nsHtml5StreamParser.h",
     "nsHtml5StreamParserPtr.h",
+    "nsHtml5StreamParserReleaser.h",
     "nsHtml5String.h",
     "nsHtml5StringParser.h",
     "nsHtml5SVGLoadDispatcher.h",

parser/html/nsHtml5StreamListener.cpp

@@ -4,6 +4,8 @@
 
 #include "nsHtml5StreamListener.h"
 
+#include "nsHtml5StreamParserReleaser.h"
+
 NS_IMPL_ADDREF(nsHtml5StreamListener)
 NS_IMPL_RELEASE(nsHtml5StreamListener)
 
@@ -15,14 +17,40 @@ NS_INTERFACE_MAP_BEGIN(nsHtml5StreamListener)
 NS_INTERFACE_MAP_END
 
 nsHtml5StreamListener::nsHtml5StreamListener(nsHtml5StreamParser* aDelegate)
-    : mDelegate(aDelegate) {}
+    : mDelegateMonitor("nsHtml5StreamListener mDelegateMonitor"),
+      mDelegate(aDelegate) {
+  MOZ_ASSERT(aDelegate, "Must have delegate");
+  aDelegate->AddRef();
+}
 
-nsHtml5StreamListener::~nsHtml5StreamListener() {}
+nsHtml5StreamListener::~nsHtml5StreamListener() { DropDelegateImpl(); }
 
 void nsHtml5StreamListener::DropDelegate() {
   MOZ_ASSERT(NS_IsMainThread(),
              "Must not call DropDelegate from non-main threads.");
-  mDelegate = nullptr;
+  DropDelegateImpl();
+}
+
+void nsHtml5StreamListener::DropDelegateImpl() {
+  mozilla::ReentrantMonitorAutoEnter autoEnter(mDelegateMonitor);
+  if (mDelegate) {
+    nsCOMPtr<nsIRunnable> releaser = new nsHtml5StreamParserReleaser(mDelegate);
+    if (NS_FAILED(mDelegate->DispatchToMain(releaser.forget()))) {
+      NS_WARNING("Failed to dispatch releaser event.");
+    }
+    mDelegate = nullptr;
+  }
+}
+
+nsHtml5StreamParser* nsHtml5StreamListener::GetDelegate() {
+  MOZ_ASSERT(NS_IsMainThread(), "Wrong thread!");
+  // Let's acquire the monitor in order to always access mDelegate
+  // with monitor held. Since this can be called only on the main
+  // thread and DropDelegate() can only be called on the main thread
+  // it's OK that the monitor here doesn't protect the use of the
+  // return value.
+  mozilla::ReentrantMonitorAutoEnter autoEnter(mDelegateMonitor);
+  return mDelegate;
 }
 
 NS_IMETHODIMP
@@ -35,6 +63,7 @@ nsHtml5StreamListener::CheckListenerChain() {
 
 NS_IMETHODIMP
 nsHtml5StreamListener::OnStartRequest(nsIRequest* aRequest) {
+  mozilla::ReentrantMonitorAutoEnter autoEnter(mDelegateMonitor);
   if (MOZ_UNLIKELY(!mDelegate)) {
     return NS_ERROR_NOT_AVAILABLE;
   }
@@ -43,6 +72,7 @@ nsHtml5StreamListener::OnStartRequest(nsIRequest* aRequest) {
 
 NS_IMETHODIMP
 nsHtml5StreamListener::OnStopRequest(nsIRequest* aRequest, nsresult aStatus) {
+  mozilla::ReentrantMonitorAutoEnter autoEnter(mDelegateMonitor);
   if (MOZ_UNLIKELY(!mDelegate)) {
     return NS_ERROR_NOT_AVAILABLE;
   }
@@ -54,6 +84,7 @@ nsHtml5StreamListener::OnDataAvailable(nsIRequest* aRequest,
                                        nsIInputStream* aInStream,
                                        uint64_t aSourceOffset,
                                        uint32_t aLength) {
+  mozilla::ReentrantMonitorAutoEnter autoEnter(mDelegateMonitor);
   if (MOZ_UNLIKELY(!mDelegate)) {
     return NS_ERROR_NOT_AVAILABLE;
   }

parser/html/nsHtml5StreamListener.h

@@ -7,8 +7,8 @@
 
 #include "nsIStreamListener.h"
 #include "nsIThreadRetargetableStreamListener.h"
-#include "nsHtml5StreamParserPtr.h"
 #include "nsHtml5StreamParser.h"
+#include "mozilla/ReentrantMonitor.h"
 
 /**
  * The purpose of this class is to reconcile the problem that
@@ -38,14 +38,23 @@ class nsHtml5StreamListener : public nsIStreamListener,
   NS_DECL_NSISTREAMLISTENER
   NS_DECL_NSITHREADRETARGETABLESTREAMLISTENER
 
-  inline nsHtml5StreamParser* GetDelegate() { return mDelegate; }
+  // Main-thread-only
+  nsHtml5StreamParser* GetDelegate();
 
+  // Main-thread-only
   void DropDelegate();
 
  private:
+  void DropDelegateImpl();
   virtual ~nsHtml5StreamListener();
 
-  nsHtml5StreamParserPtr mDelegate;
+  // ReentrantMonitor instead of Mutex, because `GetDelegate()`
+  // can be called from within the Necko callbacks when Necko events
+  // are delivered on the main thread.
+  mozilla::ReentrantMonitor mDelegateMonitor;
+  // Owning pointer with manually-managed refcounting, protected by
+  // mDelegateMonitor.
+  nsHtml5StreamParser* mDelegate;
 };
 
 #endif  // nsHtml5StreamListener_h

parser/html/nsHtml5StreamParser.h

@@ -191,6 +191,7 @@ class nsHtml5StreamParser final : public nsISupports {
   friend class nsHtml5StreamParserContinuation;
   friend class nsHtml5TimerKungFu;
   friend class nsHtml5StreamParserPtr;
+  friend class nsHtml5StreamListener;
 
  public:
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS

parser/html/nsHtml5StreamParserPtr.h

@@ -7,22 +7,10 @@
 #define nsHtml5StreamParserPtr_h
 
 #include "nsHtml5StreamParser.h"
+#include "nsHtml5StreamParserReleaser.h"
 #include "nsThreadUtils.h"
 #include "mozilla/dom/DocGroup.h"
 
-class nsHtml5StreamParserReleaser : public mozilla::Runnable {
- private:
-  nsHtml5StreamParser* mPtr;
-
- public:
-  explicit nsHtml5StreamParserReleaser(nsHtml5StreamParser* aPtr)
-      : mozilla::Runnable("nsHtml5StreamParserReleaser"), mPtr(aPtr) {}
-  NS_IMETHOD Run() override {
-    mPtr->Release();
-    return NS_OK;
-  }
-};
-
 /**
  * Like nsRefPtr except release is proxied to the main
  * thread. Mostly copied from nsRefPtr.

parser/html/nsHtml5StreamParserReleaser.h

@@ -0,0 +1,25 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsHtml5StreamParserReleaser_h
+#define nsHtml5StreamParserReleaser_h
+
+#include "nsHtml5StreamParser.h"
+#include "nsThreadUtils.h"
+
+class nsHtml5StreamParserReleaser : public mozilla::Runnable {
+ private:
+  nsHtml5StreamParser* mPtr;
+
+ public:
+  explicit nsHtml5StreamParserReleaser(nsHtml5StreamParser* aPtr)
+      : mozilla::Runnable("nsHtml5StreamParserReleaser"), mPtr(aPtr) {}
+  NS_IMETHOD Run() override {
+    mPtr->Release();
+    return NS_OK;
+  }
+};
+
+#endif // nsHtml5StreamParserReleaser_h