Bug 1406922 - Make CycleCollectedJSContext to handle microtasks and make MutationObserver to use them

Tag UXP Issue #1344

5 files changed, 164 insertions, 48 deletions

diff --git a/dom/base/nsDOMMutationObserver.cpp b/dom/base/nsDOMMutationObserver.cpp
index 858a30ce5..4c4731c11 100644
--- a/dom/base/nsDOMMutationObserver.cpp
+++ b/dom/base/nsDOMMutationObserver.cpp
@@ -32,8 +32,6 @@ using mozilla::dom::Element;
 AutoTArray<RefPtr<nsDOMMutationObserver>, 4>*
   nsDOMMutationObserver::sScheduledMutationObservers = nullptr;
 
-nsDOMMutationObserver* nsDOMMutationObserver::sCurrentObserver = nullptr;
-
 uint32_t nsDOMMutationObserver::sMutationLevel = 0;
 uint64_t nsDOMMutationObserver::sCount = 0;
 
@@ -597,10 +595,32 @@ nsDOMMutationObserver::ScheduleForRun()
   RescheduleForRun();
 }
 
+class MutationObserverMicroTask final : public MicroTaskRunnable
+{
+public:
+  virtual void Run(AutoSlowOperation& aAso) override
+  {
+    nsDOMMutationObserver::HandleMutations(aAso);
+  }
+
+  virtual bool Suppressed() override
+  {
+    return nsDOMMutationObserver::AllScheduledMutationObserversAreSuppressed();
+  }
+};
+
 void
 nsDOMMutationObserver::RescheduleForRun()
 {
   if (!sScheduledMutationObservers) {
+    CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
+    if (!ccjs) {
+      return;
+    }
+
+    RefPtr<MutationObserverMicroTask> momt =
+      new MutationObserverMicroTask();
+    ccjs->DispatchMicroTaskRunnable(momt.forget());
     sScheduledMutationObservers = new AutoTArray<RefPtr<nsDOMMutationObserver>, 4>;
   }
 
@@ -862,36 +882,9 @@ nsDOMMutationObserver::HandleMutation()
   mCallback->Call(this, mutations, *this);
 }
 
-class AsyncMutationHandler : public mozilla::Runnable
-{
-public:
-  NS_IMETHOD Run() override
-  {
-    nsDOMMutationObserver::HandleMutations();
-    return NS_OK;
-  }
-};
-
 void
-nsDOMMutationObserver::HandleMutationsInternal()
+nsDOMMutationObserver::HandleMutationsInternal(AutoSlowOperation& aAso)
 {
-  if (!nsContentUtils::IsSafeToRunScript()) {
-    nsContentUtils::AddScriptRunner(new AsyncMutationHandler());
-    return;
-  }
-  static RefPtr<nsDOMMutationObserver> sCurrentObserver;
-  if (sCurrentObserver && !sCurrentObserver->Suppressed()) {
-    // In normal cases sScheduledMutationObservers will be handled
-    // after previous mutations are handled. But in case some
-    // callback calls a sync API, which spins the eventloop, we need to still
-    // process other mutations happening during that sync call.
-    // This does *not* catch all cases, but should work for stuff running
-    // in separate tabs.
-    return;
-  }
-
-  mozilla::AutoSlowOperation aso;
-
   nsTArray<RefPtr<nsDOMMutationObserver> >* suppressedObservers = nullptr;
 
   while (sScheduledMutationObservers) {
@@ -899,20 +892,21 @@ nsDOMMutationObserver::HandleMutationsInternal()
       sScheduledMutationObservers;
     sScheduledMutationObservers = nullptr;
     for (uint32_t i = 0; i < observers->Length(); ++i) {
-      sCurrentObserver = static_cast<nsDOMMutationObserver*>((*observers)[i]);
-      if (!sCurrentObserver->Suppressed()) {
-        sCurrentObserver->HandleMutation();
+      RefPtr<nsDOMMutationObserver> currentObserver =
+        static_cast<nsDOMMutationObserver*>((*observers)[i]);
+      if (!currentObserver->Suppressed()) {
+        currentObserver->HandleMutation();
       } else {
         if (!suppressedObservers) {
           suppressedObservers = new nsTArray<RefPtr<nsDOMMutationObserver> >;
         }
-        if (!suppressedObservers->Contains(sCurrentObserver)) {
-          suppressedObservers->AppendElement(sCurrentObserver);
+        if (!suppressedObservers->Contains(currentObserver)) {
+          suppressedObservers->AppendElement(currentObserver);
         }
       }
     }
     delete observers;
-    aso.CheckForInterrupt();
+    aAso.CheckForInterrupt();
   }
 
   if (suppressedObservers) {
@@ -923,7 +917,6 @@ nsDOMMutationObserver::HandleMutationsInternal()
     delete suppressedObservers;
     suppressedObservers = nullptr;
   }
-  sCurrentObserver = nullptr;
 }
 
 nsDOMMutationRecord*
diff --git a/dom/base/nsDOMMutationObserver.h b/dom/base/nsDOMMutationObserver.h
index cde32c57b..a8babc603 100644
--- a/dom/base/nsDOMMutationObserver.h
+++ b/dom/base/nsDOMMutationObserver.h
@@ -552,13 +552,29 @@ public:
   }
 
   // static methods
-  static void HandleMutations()
+  static void HandleMutations(mozilla::AutoSlowOperation& aAso)
   {
     if (sScheduledMutationObservers) {
-      HandleMutationsInternal();
+      HandleMutationsInternal(aAso);
     }
   }
 
+  static bool AllScheduledMutationObserversAreSuppressed()
+  {
+    if (sScheduledMutationObservers) {
+      uint32_t len = sScheduledMutationObservers->Length();
+      if (len > 0) {
+        for (uint32_t i = 0; i < len; ++i) {
+          if (!(*sScheduledMutationObservers)[i]->Suppressed()) {
+            return false;
+          }
+        }
+        return true;
+      }
+    }
+    return false;
+  }
+
   static void EnterMutationHandling();
   static void LeaveMutationHandling();
 
@@ -594,7 +610,7 @@ protected:
     return false;
   }
 
-  static void HandleMutationsInternal();
+  static void HandleMutationsInternal(mozilla::AutoSlowOperation& aAso);
 
   static void AddCurrentlyHandlingObserver(nsDOMMutationObserver* aObserver,
                                            uint32_t aMutationLevel);
@@ -622,7 +638,6 @@ protected:
 
   static uint64_t                                    sCount;
   static AutoTArray<RefPtr<nsDOMMutationObserver>, 4>* sScheduledMutationObservers;
-  static nsDOMMutationObserver*                      sCurrentObserver;
 
   static uint32_t                                    sMutationLevel;
   static AutoTArray<AutoTArray<RefPtr<nsDOMMutationObserver>, 4>, 4>*
diff --git a/dom/base/test/test_mutationobservers.html b/dom/base/test/test_mutationobservers.html
index a6de89595..7e4c99423 100644
--- a/dom/base/test/test_mutationobservers.html
+++ b/dom/base/test/test_mutationobservers.html
@@ -362,7 +362,7 @@ function testChildList5() {
       is(records[5].previousSibling, c3, "");
       is(records[5].nextSibling, c5, "");
       observer.disconnect();
-      then(testAdoptNode);
+      then(testNestedMutations);
       m = null;
     });
   m.observe(div, { childList: true, subtree: true });
@@ -375,6 +375,37 @@ function testChildList5() {
   div.appendChild(emptyDF); // empty document shouldn't cause mutation records
 }
 
+function testNestedMutations() {
+  div.textContent = null;
+  div.appendChild(document.createTextNode("foo"));
+  var m2WasCalled = false;
+  m = new M(function(records, observer) {
+    is(records[0].type, "characterData", "Should have got characterData");
+    observer.disconnect();
+    m = null;
+    m3 = new M(function(records, observer) {
+      ok(m2WasCalled, "m2 should have been called before m3!");
+      is(records[0].type, "characterData", "Should have got characterData");
+      observer.disconnect();
+      then(testAdoptNode);
+      m3 = null;
+    });
+    m3.observe(div, { characterData: true, subtree: true});
+    div.firstChild.data = "foo";
+  });
+  m2 = new M(function(records, observer) {
+    m2WasCalled = true;
+    is(records[0].type, "characterData", "Should have got characterData");
+    observer.disconnect();
+    m2 = null;
+  });
+  m2.observe(div, { characterData: true, subtree: true});
+  div.appendChild(document.createTextNode("foo"));
+  m.observe(div, { characterData: true, subtree: true });
+
+  div.firstChild.data = "bar";
+}
+
 function testAdoptNode() {
   var d1 = document.implementation.createHTMLDocument(null);
   var d2 = document.implementation.createHTMLDocument(null);
diff --git a/xpcom/base/CycleCollectedJSContext.cpp b/xpcom/base/CycleCollectedJSContext.cpp
index 0a85ae6ac..033ca562a 100644
--- a/xpcom/base/CycleCollectedJSContext.cpp
+++ b/xpcom/base/CycleCollectedJSContext.cpp
@@ -440,6 +440,7 @@ CycleCollectedJSContext::CycleCollectedJSContext()
   , mDoingStableStates(false)
   , mDisableMicroTaskCheckpoint(false)
   , mMicroTaskLevel(0)
+  , mMicroTaskRecursionDepth(0)
   , mOutOfMemoryState(OOMState::OK)
   , mLargeAllocationFailureState(OOMState::OK)
 {
@@ -1380,8 +1381,8 @@ CycleCollectedJSContext::AfterProcessTask(uint32_t aRecursionDepth)
 
   // Step 4.1: Execute microtasks.
   if (!mDisableMicroTaskCheckpoint) {
+    PerformMicroTaskCheckPoint();
     if (NS_IsMainThread()) {
-      PerformMainThreadMicroTaskCheckpoint();
       Promise::PerformMicroTaskCheckpoint();
     } else {
       Promise::PerformWorkerMicroTaskCheckpoint();
@@ -1661,12 +1662,70 @@ CycleCollectedJSContext::DispatchToMicroTask(already_AddRefed<nsIRunnable> aRunn
   mPromiseMicroTaskQueue.push(runnable.forget());
 }
 
+class AsyncMutationHandler final : public mozilla::Runnable
+{
+public:
+  NS_IMETHOD Run() override
+  {
+    CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
+    if (ccjs) {
+      ccjs->PerformMicroTaskCheckPoint();
+    }
+    return NS_OK;
+  }
+};
+
 void
-CycleCollectedJSContext::PerformMainThreadMicroTaskCheckpoint()
+CycleCollectedJSContext::PerformMicroTaskCheckPoint()
 {
-  MOZ_ASSERT(NS_IsMainThread());
+  if (mPendingMicroTaskRunnables.empty()) {
+    // Nothing to do, return early.
+    return;
+  }
+
+  uint32_t currentDepth = RecursionDepth();
+  if (mMicroTaskRecursionDepth >= currentDepth) {
+    // We are already executing microtasks for the current recursion depth.
+    return;
+  }
 
-  nsDOMMutationObserver::HandleMutations();
+  if (NS_IsMainThread() && !nsContentUtils::IsSafeToRunScript()) {
+    // Special case for main thread where DOM mutations may happen when
+    // it is not safe to run scripts.
+    nsContentUtils::AddScriptRunner(new AsyncMutationHandler());
+    return;
+  }
+
+  mozilla::AutoRestore<uint32_t> restore(mMicroTaskRecursionDepth);
+  MOZ_ASSERT(currentDepth > 0);
+  mMicroTaskRecursionDepth = currentDepth;
+
+  AutoSlowOperation aso;
+
+  std::queue<RefPtr<MicroTaskRunnable>> suppressed;
+  while (!mPendingMicroTaskRunnables.empty()) {
+    RefPtr<MicroTaskRunnable> runnable =
+      mPendingMicroTaskRunnables.front().forget();
+    mPendingMicroTaskRunnables.pop();
+    if (runnable->Suppressed()) {
+      suppressed.push(runnable);
+    } else {
+      runnable->Run(aso);
+    }
+  }
+
+  // Put back the suppressed microtasks so that they will be run later.
+  // Note, it is possible that we end up keeping these suppressed tasks around
+  // for some time, but no longer than spinning the event loop nestedly
+  // (sync XHR, alert, etc.)
+  mPendingMicroTaskRunnables.swap(suppressed);
+}
+
+void
+CycleCollectedJSContext::DispatchMicroTaskRunnable(
+  already_AddRefed<MicroTaskRunnable> aRunnable)
+{
+  mPendingMicroTaskRunnables.push(aRunnable);
 }
 
 void
diff --git a/xpcom/base/CycleCollectedJSContext.h b/xpcom/base/CycleCollectedJSContext.h
index 2197eae92..4cd1479ed 100644
--- a/xpcom/base/CycleCollectedJSContext.h
+++ b/xpcom/base/CycleCollectedJSContext.h
@@ -33,6 +33,7 @@ struct Class;
 } // namespace js
 
 namespace mozilla {
+class AutoSlowOperation;
 
 class JSGCThingParticipant: public nsCycleCollectionParticipant
 {
@@ -134,6 +135,17 @@ struct CycleCollectorResults
   uint32_t mNumSlices;
 };
 
+class MicroTaskRunnable
+{
+public:
+  MicroTaskRunnable() {}
+  NS_INLINE_DECL_REFCOUNTING(MicroTaskRunnable)
+  virtual void Run(AutoSlowOperation& aAso) = 0;
+  virtual bool Suppressed() { return false; }
+protected:
+  virtual ~MicroTaskRunnable() {}
+};
+
 class CycleCollectedJSContext
 {
   friend class JSGCThingParticipant;
@@ -412,7 +424,7 @@ public:
   void LeaveMicroTask()
   {
     if (--mMicroTaskLevel == 0) {
-      PerformMainThreadMicroTaskCheckpoint();
+      PerformMicroTaskCheckPoint();
     }
   }
 
@@ -431,7 +443,9 @@ public:
     mMicroTaskLevel = aLevel;
   }
 
-  void PerformMainThreadMicroTaskCheckpoint();
+  void PerformMicroTaskCheckPoint();
+
+  void DispatchMicroTaskRunnable(already_AddRefed<MicroTaskRunnable> aRunnable);
 
   // Storage for watching rejected promises waiting for some client to
   // consume their rejection.
@@ -484,6 +498,10 @@ private:
   bool mDisableMicroTaskCheckpoint;
 
   uint32_t mMicroTaskLevel;
+  std::queue<RefPtr<MicroTaskRunnable>> mPendingMicroTaskRunnables;
+
+  uint32_t mMicroTaskRecursionDepth;
+
   OOMState mOutOfMemoryState;
   OOMState mLargeAllocationFailureState;