[RCS] Make runtime call stats work with --prof.

... by avoiding reads through timer objects allocated on stack of another thread and
explicitly maintaining current RuntimeCallCounter object in RuntimeCallStats instead.

Change-Id: I54eaf078dc1e77dc47ded963903d54ffb583f377
Reviewed-on: https://chromium-review.googlesource.com/471667Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44491}

src/counters.cc

@@ -416,6 +416,7 @@ void RuntimeCallStats::Enter(RuntimeCallStats* stats, RuntimeCallTimer* timer,
   DCHECK(counter->name() != nullptr);
   timer->Start(counter, stats->current_timer_.Value());
   stats->current_timer_.SetValue(timer);
+  stats->current_counter_.SetValue(counter);
 }
 
 // static
@@ -431,6 +432,15 @@ void RuntimeCallStats::Leave(RuntimeCallStats* stats, RuntimeCallTimer* timer) {
     if (next == nullptr) return;
     next->set_parent(timer->Stop());
   }
+
+  {
+    RuntimeCallTimer* cur_timer = stats->current_timer_.Value();
+    if (cur_timer == nullptr) {
+      stats->current_counter_.SetValue(nullptr);
+    } else {
+      stats->current_counter_.SetValue(cur_timer->counter());
+    }
+  }
 }
 
 void RuntimeCallStats::Add(RuntimeCallStats* other) {
@@ -448,7 +458,9 @@ void RuntimeCallStats::CorrectCurrentCounterId(RuntimeCallStats* stats,
   RuntimeCallTimer* timer = stats->current_timer_.Value();
   // When RCS are enabled dynamically there might be no current timer set up.
   if (timer == nullptr) return;
-  timer->set_counter(&(stats->*counter_id));
+  RuntimeCallCounter* counter = &(stats->*counter_id);
+  timer->set_counter(counter);
+  stats->current_counter_.SetValue(counter);
 }
 
 void RuntimeCallStats::Print(std::ostream& os) {

src/counters.h

@@ -859,11 +859,14 @@ class RuntimeCallStats final : public ZoneObject {
   V8_NOINLINE void Dump(v8::tracing::TracedValue* value);
 
   RuntimeCallTimer* current_timer() { return current_timer_.Value(); }
+  RuntimeCallCounter* current_counter() { return current_counter_.Value(); }
   bool InUse() { return in_use_; }
 
  private:
-  // Counter to track recursive time events.
+  // Top of a stack of active timers.
   base::AtomicValue<RuntimeCallTimer*> current_timer_;
+  // Active counter object associated with current timer.
+  base::AtomicValue<RuntimeCallCounter*> current_counter_;
   // Used to track nested tracing scopes.
   bool in_use_;
 };

src/log.cc

@@ -1295,9 +1295,7 @@ void Logger::HeapSampleItemEvent(const char* type, int number, int bytes) {
 
 void Logger::RuntimeCallTimerEvent() {
   RuntimeCallStats* stats = isolate_->counters()->runtime_call_stats();
-  RuntimeCallTimer* timer = stats->current_timer();
-  if (timer == nullptr) return;
-  RuntimeCallCounter* counter = timer->counter();
+  RuntimeCallCounter* counter = stats->current_counter();
   if (counter == nullptr) return;
   Log::MessageBuilder msg(log_);
   msg.Append("active-runtime-timer,");