From da5496eedf82806a095b1cdad085128768797e30 Mon Sep 17 00:00:00 2001
From: Kyle Huey <khuey@kylehuey.com>
Date: Mon, 6 Jun 2016 06:51:15 -0700
Subject: [PATCH] Bug 1273737: Shutdown the refresh driver when there are no
 more refresh drivers. r=dbaron,mchang

---
 layout/base/nsPresContext.cpp    | 13 +++++-------
 layout/base/nsRefreshDriver.cpp  | 36 +++++++++++++++++++++++++++-----
 layout/base/nsRefreshDriver.h    | 11 ++++------
 layout/build/nsLayoutStatics.cpp |  4 ----
 4 files changed, 40 insertions(+), 24 deletions(-)

diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index 42b4ac22ebdd..e5e33e655bb6 100644
--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -330,14 +330,7 @@ nsPresContext::Destroy()
                                   "nglayout.debug.paint_flashing_chrome",
                                   this);
 
-  // Disconnect the refresh driver *after* the transition manager, which
-  // needs it.
-  if (mRefreshDriver) {
-    if (mRefreshDriver->PresContext() == this) {
-      mRefreshDriver->Disconnect();
-    }
-    mRefreshDriver = nullptr;
-  }
+  mRefreshDriver = nullptr;
 }
 
 nsPresContext::~nsPresContext()
@@ -982,6 +975,10 @@ nsPresContext::SetShell(nsIPresShell* aShell)
       mRestyleManager->Disconnect();
       mRestyleManager = nullptr;
     }
+    if (mRefreshDriver && mRefreshDriver->PresContext() == this) {
+      mRefreshDriver->Disconnect();
+      // Can't null out the refresh driver here.
+    }
 
     if (IsRoot()) {
       nsRootPresContext* thisRoot = static_cast<nsRootPresContext*>(this);
diff --git a/layout/base/nsRefreshDriver.cpp b/layout/base/nsRefreshDriver.cpp
index a070f4c92f07..644e3397ab26 100644
--- a/layout/base/nsRefreshDriver.cpp
+++ b/layout/base/nsRefreshDriver.cpp
@@ -104,6 +104,11 @@ namespace {
   // vsync to the main thread has been delayed by at least 2^i ms. Use
   // GetJankLevels to grab a copy of this array.
   uint64_t sJankLevels[12];
+
+  // The number outstanding nsRefreshDrivers (that have been created but not
+  // disconnected). When this reaches zero we will call
+  // nsRefreshDriver::Shutdown.
+  static uint32_t sRefreshDriverCount = 0;
 }
 
 namespace mozilla {
@@ -889,11 +894,6 @@ GetFirstFrameDelay(imgIRequest* req)
   return static_cast<uint32_t>(delay);
 }
 
-/* static */ void
-nsRefreshDriver::InitializeStatics()
-{
-}
-
 /* static */ void
 nsRefreshDriver::Shutdown()
 {
@@ -1024,18 +1024,29 @@ nsRefreshDriver::nsRefreshDriver(nsPresContext* aPresContext)
     mSkippedPaints(false),
     mResizeSuppressed(false)
 {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(mPresContext,
+             "Need a pres context to tell us to call Disconnect() later "
+             "and decrement sRefreshDriverCount.");
+
   mMostRecentRefreshEpochTime = JS_Now();
   mMostRecentRefresh = TimeStamp::Now();
   mMostRecentTick = mMostRecentRefresh;
   mNextThrottledFrameRequestTick = mMostRecentTick;
   mNextRecomputeVisibilityTick = mMostRecentTick;
+
+  --sRefreshDriverCount;
 }
 
 nsRefreshDriver::~nsRefreshDriver()
 {
+  MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(ObserverCount() == 0,
              "observers should have unregistered");
   MOZ_ASSERT(!mActiveTimer, "timer should be gone");
+  MOZ_ASSERT(!mPresContext,
+             "Should have called Disconnect() and decremented "
+             "sRefreshDriverCount!");
 
   if (mRootRefresh) {
     mRootRefresh->RemoveRefreshObserver(this, Flush_Style);
@@ -2207,6 +2218,21 @@ nsRefreshDriver::CancelPendingEvents(nsIDocument* aDocument)
   }
 }
 
+void
+nsRefreshDriver::Disconnect()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+
+  StopTimer();
+
+  if (mPresContext) {
+    mPresContext = nullptr;
+    if (--sRefreshDriverCount == 0) {
+      Shutdown();
+    }
+  }
+}
+
 /* static */ bool
 nsRefreshDriver::IsJankCritical()
 {
diff --git a/layout/base/nsRefreshDriver.h b/layout/base/nsRefreshDriver.h
index cff0c19ea7d1..218d2026ab1c 100644
--- a/layout/base/nsRefreshDriver.h
+++ b/layout/base/nsRefreshDriver.h
@@ -77,9 +77,6 @@ public:
   explicit nsRefreshDriver(nsPresContext *aPresContext);
   ~nsRefreshDriver();
 
-  static void InitializeStatics();
-  static void Shutdown();
-
   /**
    * Methods for testing, exposed via nsIDOMWindowUtils.  See
    * nsIDOMWindowUtils.advanceTimeAndRefresh for description.
@@ -248,10 +245,7 @@ public:
    * should stop its timer and forget about its pres context.  This may
    * be called from within a refresh.
    */
-  void Disconnect() {
-    StopTimer();
-    mPresContext = nullptr;
-  }
+  void Disconnect();
 
   bool IsFrozen() { return mFreezeCount > 0; }
 
@@ -334,6 +328,7 @@ public:
   NS_IMETHOD_(MozExternalRefCountType) AddRef(void) override { return TransactionIdAllocator::AddRef(); }
   NS_IMETHOD_(MozExternalRefCountType) Release(void) override { return TransactionIdAllocator::Release(); }
   virtual void WillRefresh(mozilla::TimeStamp aTime) override;
+
 private:
   typedef nsTObserverArray<nsARefreshObserver*> ObserverArray;
   typedef nsTHashtable<nsISupportsHashKey> RequestTable;
@@ -463,6 +458,8 @@ private:
   void ConfigureHighPrecision();
   void SetHighPrecisionTimersEnabled(bool aEnable);
 
+  static void Shutdown();
+
   // `true` if we are currently in jank-critical mode.
   //
   // In jank-critical mode, any iteration of the event loop that takes
diff --git a/layout/build/nsLayoutStatics.cpp b/layout/build/nsLayoutStatics.cpp
index fd51537639ac..99e05c4d9b95 100644
--- a/layout/build/nsLayoutStatics.cpp
+++ b/layout/build/nsLayoutStatics.cpp
@@ -109,7 +109,6 @@ using namespace mozilla::system;
 #include "nsJSEnvironment.h"
 #include "nsContentSink.h"
 #include "nsFrameMessageManager.h"
-#include "nsRefreshDriver.h"
 #include "nsDOMMutationObserver.h"
 #include "nsHyphenationManager.h"
 #include "nsEditorSpellCheck.h"
@@ -271,7 +270,6 @@ nsLayoutStatics::Initialize()
   nsLayoutUtils::Initialize();
   nsIPresShell::InitializeStatics();
   TouchManager::InitializeStatics();
-  nsRefreshDriver::InitializeStatics();
   nsPrincipal::InitializeStatics();
 
   nsCORSListenerProxy::Startup();
@@ -434,8 +432,6 @@ nsLayoutStatics::Shutdown()
 
   ContentParent::ShutDown();
 
-  nsRefreshDriver::Shutdown();
-
   DisplayItemClip::Shutdown();
 
   nsDocument::XPCOMShutdown();