- Account for the possibility of timer objects being nested.

vm/timer.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_TIMER_H_
 #define VM_TIMER_H_
 
 #include "vm/allocation.h"
 #include "vm/flags.h"
 #include "vm/os.h"
 
 namespace dart {
 
 // Timer class allows timing of specific operations in the VM.
 class Timer : public ValueObject {
  public:
   Timer(bool enabled, const char* message)
-      : start_(0), stop_(0), total_(0), enabled_(enabled), message_(message) {}
+      : start_(0), stop_(0), total_(0),
+        enabled_(enabled), running_(false), message_(message) {}
   ~Timer() {}
 
   // Start timer.
   void Start() {
     if (enabled_) {
       start_ = OS::GetCurrentTimeMicros();
+      running_ = true;
     }
   }
 
   // Stop timer.
   void Stop() {
     if (enabled_) {
       ASSERT(start_ != 0);
+      ASSERT(running());
       stop_ = OS::GetCurrentTimeMicros();
       total_ += ElapsedMicros();
+      running_ = false;
     }
   }
 
   // Get total cummulative elapsed time in micros and reset the counters.
   int64_t TotalElapsedTime() {
     if (enabled_) {
       int64_t result = total_;
       Reset();
       return result;
     }
     return 0;
   }
 
   // Accessors.
   bool enabled() const { return enabled_; }
+  bool running() const { return running_; }
   const char* message() const { return message_; }
 
  private:
   int64_t ElapsedMicros() const {
     if (enabled_) {
       ASSERT(start_ != 0);
       ASSERT(stop_ != 0);
       return stop_ - start_;
     }
     return 0;
   }
 
   void Reset() {
     if (enabled_) {
       start_ = 0;
       stop_ = 0;
       total_ = 0;
+      running_ = false;
     }
   }
 
   int64_t start_;
   int64_t stop_;
   int64_t total_;
   bool enabled_;
+  bool running_;
   const char* message_;
 
   DISALLOW_COPY_AND_ASSIGN(Timer);
 };
 
 // List of per isolate timers.
 #define TIMER_LIST(V)                                                          \
   V(time_script_loading, "Script Loading : ")                                  \
   V(time_creating_snapshot, "Snapshot Creation : ")                            \
   V(time_isolate_initialization, "Isolate initialization : ")                  \
@@ skipping 45 matching lines @@
 // It is used as follows:
 // {
 //   TIMERSCOPE(name_of_timer);
 //   ....
 //   .....
 //   code that needs to be timed.
 //   ....
 // }
 class TimerScope : public ValueObject {
  public:
-  TimerScope(bool flag, Timer* timer) : flag_(flag), timer_(timer) {
+  TimerScope(bool flag, Timer* timer)
+      : flag_(flag), nested_(false), timer_(timer) {
     if (flag_) {
-      timer_->Start();
+      if (!timer_->running()) {
+        timer_->Start();
+      } else {
+        nested_ = true;
+      }
     }
   }
   ~TimerScope() {
     if (flag_) {
-      timer_->Stop();
+      if (!nested_) {
+        timer_->Stop();
+      }
     }
   }
 
  private:
   bool flag_;
+  bool nested_;
   Timer* timer_;
   DISALLOW_COPY_AND_ASSIGN(TimerScope);
 };
 
 #define TIMERSCOPE(name)                                                       \
   TimerScope vm_internal_timer_((FLAG_##name || FLAG_time_all),                \
                                 &(Isolate::Current()->timer_list().name()))
 
 }  // namespace dart
 
 #endif  // VM_TIMER_H_