tor-browser

commit e78b98f730ecd5918e4ee804a70a21abbe478d04
parent 3becf845e53965e579b9ecc48ea9368400907793
Author: Matthew Gaudet <mgaudet@mozilla.com>
Date:   Fri, 28 Nov 2025 16:31:03 +0000

Bug 2002849 - Revert "Bug 1997702 - Remove use of PersistentRooted on JSContext for MicroTaskQueues" r=jonco

For now let's focus on the industry benchmark rather than a microbenchmark.

Bug 2002850 has been opened to track further improvement here.

Differential Revision: https://phabricator.services.mozilla.com/D274351

Diffstat:
M
js/src/vm/JSContext.cpp
 | 
19
++++++-------------
M
js/src/vm/JSContext.h
 | 
4
++--

2 files changed, 8 insertions(+), 15 deletions(-)
diff --git a/js/src/vm/JSContext.cpp b/js/src/vm/JSContext.cpp
@@ -1067,11 +1067,9 @@ void js::MicroTaskQueueElement::trace(JSTracer* trc) {
   auto* queue = cx->jobQueue.ref();
 
   if (!queue || value.isGCThing()) {
-    TraceEdge(trc, &value, "microtask-queue-entry");
+    TraceRoot(trc, &value, "microtask-queue-entry");
   } else {
-    // It's OK to use unbarriered address here because this is not a GC thing
-    // and so there are no worthwhile barriers to consider here.
-    queue->traceNonGCThingMicroTask(trc, value.unbarrieredAddress());
+    queue->traceNonGCThingMicroTask(trc, &value);
   }
 }
 
@@ -1163,7 +1161,7 @@ JS_PUBLIC_API bool JS::HasDebuggerMicroTasks(JSContext* cx) {
 struct SavedMicroTaskQueueImpl : public JS::SavedMicroTaskQueue {
   explicit SavedMicroTaskQueueImpl(JSContext* cx) : savedQueues(cx) {
     savedQueues = js::MakeUnique<js::MicroTaskQueueSet>(cx);
-    std::swap(cx->microTaskQueues, savedQueues.get());
+    std::swap(cx->microTaskQueues.get(), savedQueues.get());
   }
   ~SavedMicroTaskQueueImpl() override = default;
   JS::PersistentRooted<js::UniquePtr<js::MicroTaskQueueSet>> savedQueues;
@@ -1186,7 +1184,7 @@ JS_PUBLIC_API void JS::RestoreMicroTaskQueue(
   // There's only one impl, so we know this is safe.
   SavedMicroTaskQueueImpl* savedQueueImpl =
       static_cast<SavedMicroTaskQueueImpl*>(savedQueue.get());
-  std::swap(savedQueueImpl->savedQueues.get(), cx->microTaskQueues);
+  std::swap(savedQueueImpl->savedQueues.get(), cx->microTaskQueues.get());
 }
 
 JS_PUBLIC_API size_t JS::GetRegularMicroTaskCount(JSContext* cx) {
@@ -1292,7 +1290,8 @@ JSContext::JSContext(JSRuntime* runtime, const JS::ContextOptions& options)
       canSkipEnqueuingJobs(this, false),
       promiseRejectionTrackerCallback(this, nullptr),
       promiseRejectionTrackerCallbackData(this, nullptr),
-      insideExclusiveDebuggerOnEval(this, nullptr) {
+      insideExclusiveDebuggerOnEval(this, nullptr),
+      microTaskQueues(this) {
   MOZ_ASSERT(static_cast<JS::RootingContext*>(this) ==
              JS::RootingContext::get(this));
 }
@@ -1538,12 +1537,6 @@ void JSContext::trace(JSTracer* trc) {
 #ifdef ENABLE_WASM_JSPI
   wasm().promiseIntegration.trace(trc);
 #endif
-
-  // Skip tracing the microtask queues on minor GC as we will be updating
-  // nursery pointers through the store buffer instead.
-  if (!trc->isTenuringTracer() && microTaskQueues) {
-    microTaskQueues->trace(trc);
-  }
 }
 
 JS::NativeStackLimit JSContext::stackLimitForJitCode(JS::StackKind kind) {
diff --git a/js/src/vm/JSContext.h b/js/src/vm/JSContext.h
@@ -166,7 +166,7 @@ struct MicroTaskQueueElement {
   void trace(JSTracer* trc);
 
  private:
-  js::HeapPtr<JS::Value> value;
+  JS::Value value;
 };
 
 // Use TempAllocPolicy to report OOM
@@ -1070,7 +1070,7 @@ struct JS_PUBLIC_API JSContext : public JS::RootingContext,
   bool hasExecutionTracer() { return false; }
 #endif
 
-  js::UniquePtr<js::MicroTaskQueueSet> microTaskQueues;
+  JS::PersistentRooted<js::UniquePtr<js::MicroTaskQueueSet>> microTaskQueues;
 }; /* struct JSContext */
 
 inline JSContext* JSRuntime::mainContextFromOwnThread() {