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+// Copyright 2007-2008 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_COUNTERS_H_
+#define V8_COUNTERS_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;
+  }
+
+  // Register an application-defined function to create
+  // a histogram for passing to the AddHistogramSample function
+  static void SetCreateHistogramFunction(CreateHistogramCallback f) {
+    create_histogram_function_ = f;
+  }
+
+  // Register an application-defined function to add a sample
+  // to a histogram created with CreateHistogram function
+  static void SetAddHistogramSampleFunction(AddHistogramSampleCallback f) {
+    add_histogram_sample_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 char* name) {
+    if (!lookup_function_) return NULL;
+    return lookup_function_(name);
+  }
+
+  // Create a histogram by name. If the create is successful,
+  // returns a non-NULL pointer for use with AddHistogramSample
+  // function. min and max define the expected minimum and maximum
+  // sample values. buckets is the maximum number of buckets
+  // that the samples will be grouped into.
+  static void *CreateHistogram(const char* name,
+                               int min,
+                               int max,
+                               size_t buckets) {
+    if (!create_histogram_function_) return NULL;
+    return create_histogram_function_(name, min, max, buckets);
+  }
+
+  // Add a sample to a histogram created with the CreateHistogram
+  // function.
+  static void AddHistogramSample(void* histogram, int sample) {
+    if (!add_histogram_sample_function_) return;
+    return add_histogram_sample_function_(histogram, sample);
+  }
+
+ private:
+  static CounterLookupCallback lookup_function_;
+  static CreateHistogramCallback create_histogram_function_;
+  static AddHistogramSampleCallback add_histogram_sample_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.
+//
+// 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.
+//
+// This class is designed to be POD initialized.  It will be registered with
+// the counter system on first use.  For example:
+//   StatsCounter c = { "c:myctr", NULL, false };
+struct StatsCounter {
+  const char* name_;
+  int* ptr_;
+  bool lookup_done_;
+
+  // 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;
+  }
+
+ protected:
+  // Returns the cached address of this counter location.
+  int* GetPtr() {
+    if (lookup_done_)
+      return ptr_;
+    lookup_done_ = true;
+    ptr_ = StatsTable::FindLocation(name_);
+    return ptr_;
+  }
+};
+
+// StatsCounterTimer t = { { L"t:foo", NULL, false }, 0, 0 };
+struct StatsCounterTimer {
+  StatsCounter counter_;
+
+  int64_t start_time_;
+  int64_t stop_time_;
+
+  // Start the timer.
+  void Start();
+
+  // Stop the timer and record the results.
+  void Stop();
+
+  // Returns true if the timer is running.
+  bool Running() {
+    return counter_.Enabled() && start_time_ != 0 && stop_time_ == 0;
+  }
+};
+
+// A HistogramTimer allows distributions of results to be created
+// HistogramTimer t = { L"foo", NULL, false, 0, 0 };
+struct HistogramTimer {
+  const char* name_;
+  void* histogram_;
+  bool lookup_done_;
+
+  int64_t start_time_;
+  int64_t stop_time_;
+
+  // Start the timer.
+  void Start();
+
+  // Stop the timer and record the results.
+  void Stop();
+
+  // Returns true if the timer is running.
+  bool Running() {
+    return (histogram_ != NULL) && (start_time_ != 0) && (stop_time_ == 0);
+  }
+
+ protected:
+  // Returns the handle to the histogram.
+  void* GetHistogram() {
+    if (!lookup_done_) {
+      lookup_done_ = true;
+      histogram_ = StatsTable::CreateHistogram(name_, 0, 10000, 50);
+    }
+    return histogram_;
+  }
+};
+
+// Helper class for scoping a HistogramTimer.
+class HistogramTimerScope BASE_EMBEDDED {
+ public:
+  explicit HistogramTimerScope(HistogramTimer* timer) :
+  timer_(timer) {
+    timer_->Start();
+  }
+  ~HistogramTimerScope() {
+    timer_->Stop();
+  }
+ private:
+  HistogramTimer* timer_;
+};
+
+
+} }  // namespace v8::internal
+
+#endif  // V8_COUNTERS_H_