From 2e8a4708cd7fa884c04727b66bea2d6166ca3e0f Mon Sep 17 00:00:00 2001
From: Michael Layzell <michael@thelayzells.com>
Date: Tue, 20 Jun 2017 15:59:46 -0400
Subject: [PATCH] Bug 1343728 - Part 3: Add StableStateEventTarget, an event
 target which runs dispatched runnables at the next stable state, r=smaug

MozReview-Commit-ID: 8dlo5Z60qsG
---
 dom/base/nsContentUtils.cpp | 59 +++++++++++++++++++++++++++++++++++++
 dom/base/nsContentUtils.h   | 12 ++++++++
 2 files changed, 71 insertions(+)

diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 931ca8fae063..b2dd845f69e1 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -326,6 +326,7 @@ nsHtml5StringParser* nsContentUtils::sHTMLFragmentParser = nullptr;
 nsIParser* nsContentUtils::sXMLFragmentParser = nullptr;
 nsIFragmentContentSink* nsContentUtils::sXMLFragmentSink = nullptr;
 bool nsContentUtils::sFragmentParsingActive = false;
+nsISerialEventTarget* nsContentUtils::sStableStateEventTarget = nullptr;
 
 #if !(defined(DEBUG) || defined(MOZ_ENABLE_JS_DUMP))
 bool nsContentUtils::sDOMWindowDumpEnabled;
@@ -519,6 +520,52 @@ class SameOriginCheckerImpl final : public nsIChannelEventSink,
   NS_DECL_NSIINTERFACEREQUESTOR
 };
 
+class StableStateEventTarget final : public nsISerialEventTarget
+{
+public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIEVENTTARGET_FULL
+private:
+  ~StableStateEventTarget() {}
+};
+
+NS_IMPL_ISUPPORTS(StableStateEventTarget, nsISerialEventTarget);
+
+bool
+StableStateEventTarget::IsOnCurrentThreadInfallible()
+{
+  return true;
+}
+
+NS_IMETHODIMP
+StableStateEventTarget::IsOnCurrentThread(bool* aResult)
+{
+  *aResult = true;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StableStateEventTarget::Dispatch(already_AddRefed<nsIRunnable> aEvent, uint32_t aFlags)
+{
+  if (NS_WARN_IF(!CycleCollectedJSContext::Get())) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  nsContentUtils::RunInStableState(Move(aEvent));
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StableStateEventTarget::DispatchFromScript(nsIRunnable* aEvent, uint32_t aFlags)
+{
+  return Dispatch(nsCOMPtr<nsIRunnable>(aEvent).forget(), aFlags);
+}
+
+NS_IMETHODIMP
+StableStateEventTarget::DelayedDispatch(already_AddRefed<nsIRunnable> aEvent, uint32_t aDelay)
+{
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
 } // namespace
 
 /**
@@ -730,6 +777,9 @@ nsContentUtils::Init()
 
   Unused << nsRFPService::GetOrCreate();
 
+  RefPtr<StableStateEventTarget> stableStateEventTarget = new StableStateEventTarget();
+  stableStateEventTarget.forget(&sStableStateEventTarget);
+
   nsCOMPtr<nsIUUIDGenerator> uuidGenerator =
     do_GetService("@mozilla.org/uuid-generator;1", &rv);
   if (NS_WARN_IF(NS_FAILED(rv))) {
@@ -2156,6 +2206,8 @@ nsContentUtils::Shutdown()
 
   NS_IF_RELEASE(sSameOriginChecker);
 
+  NS_IF_RELEASE(sStableStateEventTarget);
+
   if (sUserInteractionObserver) {
     sUserInteractionObserver->Shutdown();
     NS_RELEASE(sUserInteractionObserver);
@@ -5661,6 +5713,13 @@ nsContentUtils::RunInMetastableState(already_AddRefed<nsIRunnable> aRunnable)
   CycleCollectedJSContext::Get()->RunInMetastableState(Move(aRunnable));
 }
 
+/* static */
+nsISerialEventTarget*
+nsContentUtils::GetStableStateEventTarget()
+{
+  return sStableStateEventTarget;
+}
+
 void
 nsContentUtils::EnterMicroTask()
 {
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index ae3c5fd2ad18..da3b8c3ecb4d 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -1879,6 +1879,16 @@ public:
    */
   static void RunInMetastableState(already_AddRefed<nsIRunnable> aRunnable);
 
+  /**
+   * Returns a nsISerialEventTarget which will run any event dispatched to it
+   * once the event loop has reached a "stable state". Runnables dispatched to
+   * this event target must not cause any queued events to be processed (i.e.
+   * must not spin the event loop).
+   *
+   * See RunInStableState for more information about stable states
+   */
+  static nsISerialEventTarget* GetStableStateEventTarget();
+
   // Call EnterMicroTask when you're entering JS execution.
   // Usually the best way to do this is to use nsAutoMicroTask.
   static void EnterMicroTask();
@@ -3227,6 +3237,8 @@ private:
    */
   static bool sFragmentParsingActive;
 
+  static nsISerialEventTarget* sStableStateEventTarget;
+
   static nsString* sShiftText;
   static nsString* sControlText;
   static nsString* sMetaText;