Fixing --verify-predictable mode.

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index b73ab0bd6a6be5b171a1c1258d65e05c0c8f079f..398eaead9c6bd0793ce95bf3971797d63ac9800c 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -101,6 +101,117 @@ class MockArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
 };
 
 
+class PredictablePlatform : public Platform {
+ public:
+  PredictablePlatform() {}
+  ~PredictablePlatform() override;
+
+  bool PumpMessageLoop(v8::Isolate* isolate);
+
+  // v8::Platform implementation. This is a cut down version of default
+  // platform implementation. All background and foreground tasks are
+  // run immediately. Only delayed tasks are put in a queue.
+
+  void CallOnBackgroundThread(Task* task,
+                              ExpectedRuntime expected_runtime) override {
+    task->Run();
+    delete task;
+  }
+
+  void CallOnForegroundThread(v8::Isolate* isolate, Task* task) override {
+    task->Run();
+    delete task;
+  }
+  void CallDelayedOnForegroundThread(v8::Isolate* isolate, Task* task,
+                                     double delay_in_seconds) override;

[ulan, 2015/11/12 11:38:15]

Maybe disable memory-reducer in predictable mode? (--nomemory-reducer) and just
provide a simple implementation that calls the task immediately?

[Igor Sheludko, 2015/11/12 11:53:30]

Yes, it makes sense to disable the memory reducer in predictable mode, but the
--verify-predictable (when this platform is enabled) and --predictable are
currently two different flags. You can have the former one, but not the latter.

+
+  void CallIdleOnForegroundThread(v8::Isolate* isolate,
+                                  IdleTask* task) override {
+    UNREACHABLE();
+  }
+
+  bool IdleTasksEnabled(v8::Isolate* isolate) override { return false; }
+
+  double MonotonicallyIncreasingTime() override {
+    return synthetic_time_in_sec_ += 0.000001;
+  }
+
+ private:
+  Task* PopTaskInMainThreadDelayedQueue(v8::Isolate* isolate);
+
+  base::Mutex lock_;
+
+  typedef std::pair<double, Task*> DelayedEntry;
+  struct DelayedEntryGreater {
+    bool operator()(const DelayedEntry& a, const DelayedEntry& b) {
+      return a.first > b.first;
+    }
+  };
+  std::map<v8::Isolate*,
+           std::priority_queue<DelayedEntry, std::vector<DelayedEntry>,
+                               DelayedEntryGreater> >
+      main_thread_delayed_queue_;
+
+  double synthetic_time_in_sec_ = 0.0;
+
+  DISALLOW_COPY_AND_ASSIGN(PredictablePlatform);
+};
+
+
+PredictablePlatform::~PredictablePlatform() {
+  base::LockGuard<base::Mutex> guard(&lock_);
+  for (auto i = main_thread_delayed_queue_.begin();
+       i != main_thread_delayed_queue_.end(); ++i) {
+    while (!i->second.empty()) {
+      delete i->second.top().second;
+      i->second.pop();
+    }
+  }
+}
+
+
+Task* PredictablePlatform::PopTaskInMainThreadDelayedQueue(
+    v8::Isolate* isolate) {
+  auto it = main_thread_delayed_queue_.find(isolate);
+  if (it == main_thread_delayed_queue_.end() || it->second.empty()) {
+    return NULL;
+  }
+  double now = MonotonicallyIncreasingTime();
+  DelayedEntry deadline_and_task = it->second.top();
+  if (deadline_and_task.first > now) {
+    return NULL;
+  }
+  it->second.pop();
+  return deadline_and_task.second;
+}
+
+
+bool PredictablePlatform::PumpMessageLoop(v8::Isolate* isolate) {
+  bool executed = false;
+  Task* task = NULL;
+  for (;;) {
+    {
+      base::LockGuard<base::Mutex> guard(&lock_);
+      task = PopTaskInMainThreadDelayedQueue(isolate);
+    }
+    if (task == NULL) break;
+
+    executed = true;
+    task->Run();
+    delete task;
+  }
+  return executed;
+}
+
+
+void PredictablePlatform::CallDelayedOnForegroundThread(
+    v8::Isolate* isolate, Task* task, double delay_in_seconds) {
+  base::LockGuard<base::Mutex> guard(&lock_);
+  double deadline = MonotonicallyIncreasingTime() + delay_in_seconds;
+  main_thread_delayed_queue_[isolate].push(std::make_pair(deadline, task));
+}
+
+
 v8::Platform* g_platform = NULL;
 
 
@@ -425,13 +536,11 @@ int PerIsolateData::RealmIndexOrThrow(
 
 #ifndef V8_SHARED
 // performance.now() returns a time stamp as double, measured in milliseconds.
-// When FLAG_verify_predictable mode is enabled it returns current value
-// of Heap::allocations_count().
+// When FLAG_verify_predictable mode is enabled it returns result of
+// v8::Platform::MonotonicallyIncreasingTime().
 void Shell::PerformanceNow(const v8::FunctionCallbackInfo<v8::Value>& args) {
   if (i::FLAG_verify_predictable) {
-    Isolate* v8_isolate = args.GetIsolate();
-    i::Heap* heap = reinterpret_cast<i::Isolate*>(v8_isolate)->heap();
-    args.GetReturnValue().Set(heap->synthetic_time());
+    args.GetReturnValue().Set(g_platform->MonotonicallyIncreasingTime());
   } else {
     base::TimeDelta delta =
         base::TimeTicks::HighResolutionNow() - kInitialTicks;
@@ -2016,7 +2125,13 @@ void Shell::CollectGarbage(Isolate* isolate) {
 
 
 void Shell::EmptyMessageQueues(Isolate* isolate) {
-  while (v8::platform::PumpMessageLoop(g_platform, isolate)) continue;
+  if (i::FLAG_verify_predictable) {
+    PredictablePlatform* platform =
+        reinterpret_cast<PredictablePlatform*>(g_platform);
+    while (platform->PumpMessageLoop(isolate)) continue;
+  } else {
+    while (v8::platform::PumpMessageLoop(g_platform, isolate)) continue;
+  }
 }
 
 
@@ -2358,7 +2473,9 @@ int Shell::Main(int argc, char* argv[]) {
 #endif  // defined(_WIN32) || defined(_WIN64)
   if (!SetOptions(argc, argv)) return 1;
   v8::V8::InitializeICU(options.icu_data_file);
-  g_platform = v8::platform::CreateDefaultPlatform();
+  g_platform = i::FLAG_verify_predictable
+                   ? new PredictablePlatform()
+                   : v8::platform::CreateDefaultPlatform();
   v8::V8::InitializePlatform(g_platform);
   v8::V8::Initialize();
   if (options.natives_blob || options.snapshot_blob) {