src/counters.h

// Copyright 2007-2008 Google Inc. All Rights Reserved.
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//
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#ifndef V8_COUNTERS_H_
#define V8_COUNTERS_H_

#include <wchar.h>

namespace v8 { namespace internal {

// StatsCounters is an interface for plugging into external
// counters for monitoring.  Counters can be looked up and
// manipulated by name.

class StatsTable : public AllStatic {
 public:
  // Register an application-defined function where
  // counters can be looked up.
  static void SetCounterFunction(CounterLookupCallback f) {
    lookup_function_ = f;
  }

  static bool HasCounterFunction() {
    return lookup_function_ != NULL;
  }

  // Lookup the location of a counter by name.  If the lookup
  // is successful, returns a non-NULL pointer for writing the
  // value of the counter.  Each thread calling this function
  // may receive a different location to store it's counter.
  // The return value must not be cached and re-used across
  // threads, although a single thread is free to cache it.
  static int *FindLocation(const wchar_t* name) {
    if (!lookup_function_) return NULL;
    return lookup_function_(name);
  }

 private:
  static CounterLookupCallback lookup_function_;
};

// StatsCounters are dynamically created values which can be tracked in
// the StatsTable.  They are designed to be lightweight to create and
// easy to use.
//
// The implementation of the StatsTable is external to this module.
//
// Example usage:
//    {
//      StatsCounter request_count("RequestCount");
//      request_count.Increment();
//    }
//
// Internally, a counter represents a value in a row of a StatsTable.
// The row has a 32bit value for each process/thread in the table and also
// a name (stored in the table metadata).  Since the storage location can be
// thread-specific, this class cannot be shared across threads.
//

// StatsCounter represents a counter in the StatsTable class.
class StatsCounter BASE_EMBEDDED {
 public:
  // Create a StatsCounter object.
  explicit StatsCounter(const wchar_t* name, int id) :
      lookup_done_(false),
      ptr_(NULL),
      id_(id) {
    int len = wcslen(name);
    // we prepend the name with 'c:' to indicate that it is a counter.
    name_ = NewArray<wchar_t>(len+3);
    wcscpy(name_, L"c:");
    wcscpy(&name_[2], name);
  };

  ~StatsCounter() {
    DeleteArray(name_);
  }

  // Sets the counter to a specific value.
  void Set(int value) {
    int* loc = GetPtr();
    if (loc) *loc = value;
  }

  // Increments the counter.
  void Increment() {
    int* loc = GetPtr();
    if (loc) (*loc)++;
  }

  void Increment(int value) {
    int* loc = GetPtr();
    if (loc)
      (*loc) += value;
  }

  // Decrements the counter.
  void Decrement() {
    int* loc = GetPtr();
    if (loc) (*loc)--;
  }

  void Decrement(int value) {
    int* loc = GetPtr();
    if (loc) (*loc) -= value;
  }

  // Is this counter enabled?
  // Returns false if table is full.
  bool Enabled() {
    return GetPtr() != NULL;
  }

  // Get the internal pointer to the counter. This is used
  // by the code generator to emit code that manipulates a
  // given counter without calling the runtime system.
  int* GetInternalPointer() {
    int* loc = GetPtr();
    ASSERT(loc != NULL);
    return loc;
  }

  int Id() {
    return id_;
  }

 protected:
  StatsCounter() :
      lookup_done_(false),
      ptr_(NULL) {
  }

  // Returns the cached address of this counter location.
  int* GetPtr() {
    if (lookup_done_)
      return ptr_;
    lookup_done_ = true;
    ptr_ = StatsTable::FindLocation(name_);
    return ptr_;
  }

  wchar_t* name_;
  bool lookup_done_;
  int* ptr_;
  int id_;
};

// A StatsCounterTimer is a StatsCounter which keeps a timer during
// the scope of the StatsCounterTimer.  On destruction, it will record
// its time measurement.
class StatsCounterTimer : StatsCounter {
 public:
  // Constructs and starts the timer.
  explicit StatsCounterTimer(const wchar_t* name);

  // Start the timer.
  void Start();

  // Stop the timer and record the results.
  void Stop();

  // Returns true if the timer is running.
  bool Running() {
    return Enabled() && start_time_ != 0 && stop_time_ == 0;
  }

 private:
  // Compute the delta between start and stop, in milliseconds.
  void Record() {
    int milliseconds = static_cast<int>(stop_time_ - start_time_) / 1000;
    Increment(milliseconds);
  }

  int64_t start_time_;
  int64_t stop_time_;
};


// A StatsRate is a combination of both a timer and a counter so that
// several statistics can be produced:
//    min, max, avg, count, total
class StatsRate BASE_EMBEDDED {
 public:
  // Constructs and starts the timer.
  explicit StatsRate(const wchar_t* name, int id) :
      timer_(name),
      counter_(name, id) {
  }

  // Starts the rate timer.
  void Start() {
    timer_.Start();
  }

  // Stops the rate and records the time.
  void Stop() {
    if (timer_.Running()) {
      timer_.Stop();
      counter_.Increment();
    }
  }

  // Access to the timer.
  StatsCounterTimer& timer() { return timer_; }

 private:
  StatsCounterTimer timer_;
  StatsCounter counter_;
};


// Helper class for scoping a timer.
class StatsTimerScope BASE_EMBEDDED {
 public:
  explicit StatsTimerScope(StatsCounterTimer* timer) :
      timer_(timer) {
    timer_->Start();
  }
  ~StatsTimerScope() {
    timer_->Stop();
  }
 private:
  StatsCounterTimer* timer_;
};

// Helper class for scoping a rate.
class StatsRateScope BASE_EMBEDDED {
 public:
  explicit StatsRateScope(StatsRate* rate) :
      rate_(rate) {
    rate_->Start();
  }
  ~StatsRateScope() {
    rate_->Stop();
  }
 private:
  StatsRate* rate_;
};


} }  // namespace v8::internal

#endif  // V8_COUNTERS_H_