Reland "Expose the number of microtasks from RunMicrotasks"

This is a reland of 516d9068

Original change's description:
> Expose the number of microtasks from RunMicrotasks
>
> This CL adds the number of processed microtasks to the tracing marker
> of RunMicrotasks, plus let RunMicrotasks return the number.
>
> Bug: v8:7804, v8:8124
> Change-Id: Ie584e22964121fbda3a822379d760e7518fc54a7
> Reviewed-on: https://chromium-review.googlesource.com/c/1425277
> Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#59017}

Bug: v8:7804, v8:8124
Change-Id: I4a57ba3e23973f6b46414c4502244091c42cf532
Reviewed-on: https://chromium-review.googlesource.com/c/1430399Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59148}

src/builtins/builtins-microtask-queue-gen.cc

@@ -35,6 +35,7 @@ class MicrotaskQueueBuiltinsAssembler : public CodeStubAssembler {
                                            TNode<IntPtrT> index);
   void RunSingleMicrotask(TNode<Context> current_context,
                           TNode<Microtask> microtask);
+  void IncrementFinishedMicrotaskCount(TNode<RawPtrT> microtask_queue);
 
   TNode<Context> GetCurrentContext();
   void SetCurrentContext(TNode<Context> context);
@@ -311,6 +312,17 @@ void MicrotaskQueueBuiltinsAssembler::RunSingleMicrotask(
   BIND(&done);
 }
 
+void MicrotaskQueueBuiltinsAssembler::IncrementFinishedMicrotaskCount(
+    TNode<RawPtrT> microtask_queue) {
+  TNode<IntPtrT> count = UncheckedCast<IntPtrT>(
+      Load(MachineType::IntPtr(), microtask_queue,
+           IntPtrConstant(MicrotaskQueue::kFinishedMicrotaskCountOffset)));
+  TNode<IntPtrT> new_count = IntPtrAdd(count, IntPtrConstant(1));
+  StoreNoWriteBarrier(
+      MachineType::PointerRepresentation(), microtask_queue,
+      IntPtrConstant(MicrotaskQueue::kFinishedMicrotaskCountOffset), new_count);
+}
+
 TNode<Context> MicrotaskQueueBuiltinsAssembler::GetCurrentContext() {
   auto ref = ExternalReference::Create(kContextAddress, isolate());
   return TNode<Context>::UncheckedCast(
@@ -531,6 +543,7 @@ TF_BUILTIN(RunMicrotasks, MicrotaskQueueBuiltinsAssembler) {
   SetMicrotaskQueueStart(microtask_queue, new_start);
 
   RunSingleMicrotask(current_context, microtask);
+  IncrementFinishedMicrotaskCount(microtask_queue);
   Goto(&loop);
 
   BIND(&done);

src/microtask-queue.cc

@@ -25,6 +25,8 @@ const size_t MicrotaskQueue::kCapacityOffset =
     OFFSET_OF(MicrotaskQueue, capacity_);
 const size_t MicrotaskQueue::kSizeOffset = OFFSET_OF(MicrotaskQueue, size_);
 const size_t MicrotaskQueue::kStartOffset = OFFSET_OF(MicrotaskQueue, start_);
+const size_t MicrotaskQueue::kFinishedMicrotaskCountOffset =
+    OFFSET_OF(MicrotaskQueue, finished_microtask_count_);
 
 const intptr_t MicrotaskQueue::kMinimumCapacity = 8;
 
@@ -114,20 +116,27 @@ int MicrotaskQueue::RunMicrotasks(Isolate* isolate) {
     return 0;
   }
 
+  intptr_t base_count = finished_microtask_count_;
+
   HandleScope handle_scope(isolate);
   MaybeHandle<Object> maybe_exception;
 
   MaybeHandle<Object> maybe_result;
 
+  int processed_microtask_count;
   {
     SetIsRunningMicrotasks scope(&is_running_microtasks_);
     v8::Isolate::SuppressMicrotaskExecutionScope suppress(
         reinterpret_cast<v8::Isolate*>(isolate));
     HandleScopeImplementer::EnteredContextRewindScope rewind_scope(
         isolate->handle_scope_implementer());
-    TRACE_EVENT0("v8.execute", "RunMicrotasks");
+    TRACE_EVENT_BEGIN0("v8.execute", "RunMicrotasks");
     TRACE_EVENT_CALL_STATS_SCOPED(isolate, "v8", "V8.RunMicrotasks");
     maybe_result = Execution::TryRunMicrotasks(isolate, this, &maybe_exception);
+    processed_microtask_count =
+        static_cast<int>(finished_microtask_count_ - base_count);
+    TRACE_EVENT_END1("v8.execute", "RunMicrotasks", "microtask_count",
+                     processed_microtask_count);
   }
 
   // If execution is terminating, clean up and propagate that to TryCatch scope.
@@ -144,8 +153,7 @@ int MicrotaskQueue::RunMicrotasks(Isolate* isolate) {
   DCHECK_EQ(0, size());
   OnCompleted(isolate);
 
-  // TODO(tzik): Return the number of microtasks run in this round.
-  return 0;
+  return processed_microtask_count;
 }
 
 void MicrotaskQueue::IterateMicrotasks(RootVisitor* visitor) {

src/microtask-queue.h

@@ -37,9 +37,9 @@ class V8_EXPORT_PRIVATE MicrotaskQueue {
 
   void EnqueueMicrotask(Microtask microtask);
 
-  // Returns -1 if the execution is terminating, otherwise, returns 0.
-  // TODO(tzik): Update the implementation to return the number of processed
-  // microtasks.
+  // Runs all queued Microtasks.
+  // Returns -1 if the execution is terminating, otherwise, returns the number
+  // of microtasks that ran in this round.
   int RunMicrotasks(Isolate* isolate);
 
   // Iterate all pending Microtasks in this queue as strong roots, so that
@@ -86,6 +86,7 @@ class V8_EXPORT_PRIVATE MicrotaskQueue {
   static const size_t kCapacityOffset;
   static const size_t kSizeOffset;
   static const size_t kStartOffset;
+  static const size_t kFinishedMicrotaskCountOffset;
 
   static const intptr_t kMinimumCapacity;
 
@@ -103,6 +104,9 @@ class V8_EXPORT_PRIVATE MicrotaskQueue {
   intptr_t start_ = 0;
   Address* ring_buffer_ = nullptr;
 
+  // The number of finished microtask.
+  intptr_t finished_microtask_count_ = 0;
+
   // MicrotaskQueue instances form a doubly linked list loop, so that all
   // instances are reachable through |next_|.
   MicrotaskQueue* next_ = nullptr;

test/unittests/microtask-queue-unittest.cc

@@ -88,7 +88,7 @@ TEST_F(MicrotaskQueueTest, EnqueueAndRun) {
   }));
   EXPECT_EQ(MicrotaskQueue::kMinimumCapacity, microtask_queue()->capacity());
   EXPECT_EQ(1, microtask_queue()->size());
-  microtask_queue()->RunMicrotasks(isolate());
+  EXPECT_EQ(1, microtask_queue()->RunMicrotasks(isolate()));
   EXPECT_TRUE(ran);
   EXPECT_EQ(0, microtask_queue()->size());
 }
@@ -100,7 +100,7 @@ TEST_F(MicrotaskQueueTest, BufferGrowth) {
   // Enqueue and flush the queue first to have non-zero |start_|.
   microtask_queue()->EnqueueMicrotask(
       *NewMicrotask([&count] { EXPECT_EQ(0, count++); }));
-  microtask_queue()->RunMicrotasks(isolate());
+  EXPECT_EQ(1, microtask_queue()->RunMicrotasks(isolate()));
 
   EXPECT_LT(0, microtask_queue()->capacity());
   EXPECT_EQ(0, microtask_queue()->size());
@@ -122,7 +122,8 @@ TEST_F(MicrotaskQueueTest, BufferGrowth) {
   EXPECT_EQ(MicrotaskQueue::kMinimumCapacity + 1, microtask_queue()->size());
 
   // Run all pending Microtasks to ensure they run in the proper order.
-  microtask_queue()->RunMicrotasks(isolate());
+  EXPECT_EQ(MicrotaskQueue::kMinimumCapacity + 1,
+            microtask_queue()->RunMicrotasks(isolate()));
   EXPECT_EQ(MicrotaskQueue::kMinimumCapacity + 2, count);
 }
 
@@ -163,7 +164,8 @@ TEST_F(MicrotaskQueueTest, VisitRoot) {
   for (int i = 0; i < MicrotaskQueue::kMinimumCapacity / 2 + 1; ++i) {
     microtask_queue()->EnqueueMicrotask(*NewMicrotask([] {}));
   }
-  microtask_queue()->RunMicrotasks(isolate());
+  EXPECT_EQ(MicrotaskQueue::kMinimumCapacity / 2 + 1,
+            microtask_queue()->RunMicrotasks(isolate()));
 
   std::vector<Object> expected;
   for (int i = 0; i < MicrotaskQueue::kMinimumCapacity / 2 + 1; ++i) {