1 files changed, 70 insertions, 1 deletions
diff --git a/xpcom/base/CycleCollectedJSContext.cpp b/xpcom/base/CycleCollectedJSContext.cpp
index e16c15455..033ca562a 100644
--- a/xpcom/base/CycleCollectedJSContext.cpp
+++ b/xpcom/base/CycleCollectedJSContext.cpp
@@ -79,6 +79,7 @@
 #include "nsCycleCollectionParticipant.h"
 #include "nsCycleCollector.h"
 #include "nsDOMJSUtils.h"
+#include "nsDOMMutationObserver.h"
 #include "nsJSUtils.h"
 #include "nsWrapperCache.h"
 
@@ -438,6 +439,8 @@ CycleCollectedJSContext::CycleCollectedJSContext()
   , mJSHolders(256)
   , mDoingStableStates(false)
   , mDisableMicroTaskCheckpoint(false)
+  , mMicroTaskLevel(0)
+  , mMicroTaskRecursionDepth(0)
   , mOutOfMemoryState(OOMState::OK)
   , mLargeAllocationFailureState(OOMState::OK)
 {
@@ -1378,8 +1381,8 @@ CycleCollectedJSContext::AfterProcessTask(uint32_t aRecursionDepth)
 
   // Step 4.1: Execute microtasks.
   if (!mDisableMicroTaskCheckpoint) {
+    PerformMicroTaskCheckPoint();
     if (NS_IsMainThread()) {
-      nsContentUtils::PerformMainThreadMicroTaskCheckpoint();
       Promise::PerformMicroTaskCheckpoint();
     } else {
       Promise::PerformWorkerMicroTaskCheckpoint();
@@ -1659,6 +1662,72 @@ 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::PerformMicroTaskCheckPoint()
+{
+  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;
+  }
+
+  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
 CycleCollectedJSContext::EnvironmentPreparer::invoke(JS::HandleObject scope,
                                                      js::ScriptEnvironmentPreparer::Closure& closure)