[counters] RuntimeStats: fix wrong bookkeeping when dynamically changing counters.

src/counters-inl.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COUNTERS_INL_H_
 #define V8_COUNTERS_INL_H_
 
 #include "src/counters.h"
 
 namespace v8 {
 namespace internal {
 
+void RuntimeCallTimer::Start(RuntimeCallCounter* counter,
+                             RuntimeCallTimer* parent) {
+  counter_ = counter;
+  parent_.SetValue(parent);
+  if (FLAG_runtime_stats !=
+      v8::tracing::TracingCategoryObserver::ENABLED_BY_SAMPLING) {
+    timer_.Start();
+  }
+}
+
+RuntimeCallTimer* RuntimeCallTimer::Stop() {
+  if (!timer_.IsStarted()) return parent();
+  base::TimeDelta delta = timer_.Elapsed();
+  timer_.Stop();
+  counter_->count++;
+  counter_->time += delta;
+  if (parent()) {
+    // Adjust parent timer so that it does not include sub timer's time.
+    parent()->Subtract(delta);
+  }
+  return parent();
+}
+
+void RuntimeCallTimer::Subtract(base::TimeDelta delta) {
+  // Adjust the current timer instead of directly subtracting the sub-timers
+  // from the current counter. This way we can easily change the counter of an
+  // active timer scope. Otherwise we would end up subtracting the time from the
+  // previous counter and add the own time to the newly changed counter.
+  timer_.Subtract(delta);
+}
+
+void RuntimeCallTimer::Snapshot() {
+  base::TimeTicks now = base::TimeTicks::HighResolutionNow();
+  RuntimeCallTimer* timer = this;
+  base::TimeDelta delta = base::TimeDeltae::FromMicroseconds(0);

[Igor Sheludko, 2016/11/21 10:54:02]

s/TimeDeltae/TimeDelta/

+  // Walk up the timer chain until the the timer doesn't have a parent.
+  while (timer != nullptr) {
+    // Iteration 1:   subtract 0 from the the current timer (this).

[Igor Sheludko, 2016/11/21 10:54:02]

s/the the/the/

+    // Iteration n+1: subtract the time (delta) from the subtimer.

[Igor Sheludko, 2016/11/21 10:54:02]

subtract subtimer's time (delta) from the the current timer.

+    timer->Subtract(delta);
+    delta = timer->timer_.Restart(now);
+    timer->counter_->time += delta;
+    timer = timer->parent();
+  }
+}
+
 RuntimeCallTimerScope::RuntimeCallTimerScope(
     Isolate* isolate, RuntimeCallStats::CounterId counter_id) {
   if (V8_UNLIKELY(FLAG_runtime_stats)) {
     Initialize(isolate->counters()->runtime_call_stats(), counter_id);
   }
 }
 
 RuntimeCallTimerScope::RuntimeCallTimerScope(
     HeapObject* heap_object, RuntimeCallStats::CounterId counter_id) {
   RuntimeCallTimerScope(heap_object->GetIsolate(), counter_id);
 }
 
 RuntimeCallTimerScope::RuntimeCallTimerScope(
     RuntimeCallStats* stats, RuntimeCallStats::CounterId counter_id) {
   if (V8_UNLIKELY(FLAG_runtime_stats)) {
     Initialize(stats, counter_id);
   }
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COUNTERS_INL_H_