[heap] Do not scan main thread handles when starting marking

We do not need to scan main thread handles when starting incremental
marking. This reduces the time to start incremental marking.

Bug: v8:11645
Change-Id: Ib99a13e7875f50fbfe5346ac0e186d8960ea1337
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2826124Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73994}

src/heap/heap.cc

@@ -4493,8 +4493,10 @@ void Heap::IterateRoots(RootVisitor* v, base::EnumSet<SkipRoot> options) {
     // Iterate over local handles in handle scopes.
     FixStaleLeftTrimmedHandlesVisitor left_trim_visitor(this);
 #ifndef V8_ENABLE_CONSERVATIVE_STACK_SCANNING
-    isolate_->handle_scope_implementer()->Iterate(&left_trim_visitor);
-    isolate_->handle_scope_implementer()->Iterate(v);
+    if (!options.contains(SkipRoot::kMainThreadHandles)) {
+      isolate_->handle_scope_implementer()->Iterate(&left_trim_visitor);
+      isolate_->handle_scope_implementer()->Iterate(v);
+    }
 #endif
 
     safepoint_->Iterate(&left_trim_visitor);

src/heap/heap.h

@@ -176,6 +176,7 @@ enum class SkipRoot {
   kGlobalHandles,
   kOldGeneration,
   kStack,
+  kMainThreadHandles,
   kUnserializable,
   kWeak
 };

src/heap/incremental-marking.cc

@@ -318,7 +318,9 @@ void IncrementalMarking::MarkRoots() {
 
   IncrementalMarkingRootMarkingVisitor visitor(this);
   heap_->IterateRoots(
-      &visitor, base::EnumSet<SkipRoot>{SkipRoot::kStack, SkipRoot::kWeak});
+      &visitor,
+      base::EnumSet<SkipRoot>{SkipRoot::kStack, SkipRoot::kMainThreadHandles,
+                              SkipRoot::kWeak});
 }
 
 bool IncrementalMarking::ShouldRetainMap(Map map, int age) {

test/cctest/heap/test-array-buffer-tracker.cc

@@ -269,6 +269,10 @@ TEST(ArrayBuffer_LivePromotion) {
       Handle<JSArrayBuffer> buf = v8::Utils::OpenHandle(*ab);
       root->set(0, *buf);  // Buffer that should be promoted as live.
     }
+    // Store array in Global such that it is part of the root set when
+    // starting incremental marking.
+    v8::Global<Value> global_root(CcTest::isolate(),
+                                  Utils::ToLocal(Handle<Object>::cast(root)));
     heap::SimulateIncrementalMarking(heap, true);
     CHECK(IsTracked(heap, JSArrayBuffer::cast(root->get(0))));
     heap::GcAndSweep(heap, NEW_SPACE);

test/cctest/heap/test-concurrent-marking.cc

@@ -112,6 +112,12 @@ TEST(ConcurrentMarkingMarkedBytes) {
   Handle<FixedArray> root = isolate->factory()->NewFixedArray(1000000);
   CcTest::CollectAllGarbage();
   if (!heap->incremental_marking()->IsStopped()) return;
+
+  // Store array in Global such that it is part of the root set when
+  // starting incremental marking.
+  v8::Global<Value> global_root(CcTest::isolate(),
+                                Utils::ToLocal(Handle<Object>::cast(root)));
+
   heap::SimulateIncrementalMarking(heap, false);
   heap->concurrent_marking()->Join();
   CHECK_GE(heap->concurrent_marking()->TotalMarkedBytes(), root->Size());

test/cctest/heap/test-heap.cc

@@ -2304,6 +2304,11 @@ TEST(InstanceOfStubWriteBarrier) {
   v8::HandleScope outer_scope(CcTest::isolate());
   v8::Local<v8::Context> ctx = CcTest::isolate()->GetCurrentContext();
 
+  // Store native context in global as well to make it part of the root set when
+  // starting incremental marking. This will ensure that function will be part
+  // of the transitive closure during incremental marking.
+  v8::Global<v8::Context> global_ctx(CcTest::isolate(), ctx);
+
   {
     v8::HandleScope scope(CcTest::isolate());
     CompileRun(
@@ -5218,6 +5223,10 @@ void CheckMapRetainingFor(int n) {
   Handle<Context> context = Utils::OpenHandle(*ctx);
   CHECK(context->IsNativeContext());
   Handle<NativeContext> native_context = Handle<NativeContext>::cast(context);
+  // This global is used to visit the object's constructor alive when starting
+  // incremental marking. The native context keeps the constructor alive. The
+  // constructor needs to be alive to retain the map.
+  v8::Global<v8::Context> global_ctxt(CcTest::isolate(), ctx);
 
   ctx->Enter();
   Handle<WeakFixedArray> array_with_map =
@@ -5702,11 +5711,17 @@ TEST(Regress598319) {
           get().set(i, *tmp);
         }
       }
+      global_root.Reset(CcTest::isolate(),
+                        Utils::ToLocal(Handle<Object>::cast(root)));
     }
 
     FixedArray get() { return FixedArray::cast(root->get(0)); }
 
     Handle<FixedArray> root;
+
+    // Store array in global as well to make it part of the root set when
+    // starting incremental marking.
+    v8::Global<Value> global_root;
   } arr(isolate, kNumberOfObjects);
 
   CHECK_EQ(arr.get().length(), kNumberOfObjects);

test/cctest/heap/test-write-barrier.cc

@@ -75,7 +75,11 @@ HEAP_TEST(WriteBarrier_MarkingExtension) {
   CHECK(collector->marking_state()->IsWhite(host));
   CHECK(!extension->IsMarked());
   WriteBarrier::Marking(host, extension);
+  // Concurrent marking barrier should mark this object.
   CHECK_EQ(V8_CONCURRENT_MARKING_BOOL, extension->IsMarked());
+  // Keep object alive using the global handle.
+  v8::Global<ArrayBuffer> global_host(CcTest::isolate(),
+                                      Utils::ToLocal(handle(host, isolate)));
   heap::SimulateIncrementalMarking(CcTest::heap(), true);
   CHECK(collector->marking_state()->IsBlack(host));
   CHECK(extension->IsMarked());

test/cctest/test-js-weak-refs.cc

@@ -892,6 +892,11 @@ TEST(JSWeakRefScavengedInWorklist) {
       weak_ref = inner_scope.CloseAndEscape(inner_weak_ref);
     }
 
+    // Store weak_ref in Global such that it is part of the root set when
+    // starting incremental marking.
+    v8::Global<Value> global_weak_ref(
+        CcTest::isolate(), Utils::ToLocal(Handle<Object>::cast(weak_ref)));
+
     // Do marking. This puts the WeakRef above into the js_weak_refs worklist
     // since its target isn't marked.
     CHECK(
@@ -934,6 +939,10 @@ TEST(JSWeakRefTenuredInWorklist) {
 
     weak_ref = inner_scope.CloseAndEscape(inner_weak_ref);
   }
+  // Store weak_ref such that it is part of the root set when starting
+  // incremental marking.
+  v8::Global<Value> global_weak_ref(
+      CcTest::isolate(), Utils::ToLocal(Handle<Object>::cast(weak_ref)));
   JSWeakRef old_weak_ref_location = *weak_ref;
 
   // Do marking. This puts the WeakRef above into the js_weak_refs worklist