Factor out a Histogram class from HistogramTimer, and use it to measure external fragmentation

src/counters.h

Index: src/counters.h
diff --git a/src/counters.h b/src/counters.h
index 6498a0242f9246a1d638bcd55f620971bf135740..f31b12db4884d5cc53b1d7cc7333eee2fbfff29f 100644
--- a/src/counters.h
+++ b/src/counters.h
@@ -199,25 +199,27 @@ struct StatsCounterTimer {
   }
 };
 
-// A HistogramTimer allows distributions of results to be created
-// HistogramTimer t = { L"foo", NULL, false, 0, 0 };
-struct HistogramTimer {
+// Similar to StatsCounter, the class Histogram represents a dynamically

[Michael Starzinger, 2012/07/02 21:09:56]

Can we remove the reference to StatsCounter here? Just "A Histogram represents
[...]"

[jochen (gone - plz use gerrit), 2012/07/13 09:48:08]

Done.

+// created histogram in the StatsTable.
+//
+// This class is designed to be POD initialized.  It will be registered with
+// the histogram system on first use.  For example:
+//   Histogram h = { "myhist", 0, 10000, 50, NULL, false };
+struct Histogram {
   const char* name_;
+  int min_;
+  int max_;
+  int num_buckets_;
   void* histogram_;
   bool lookup_done_;
 
-  int64_t start_time_;
-  int64_t stop_time_;
-
-  // Start the timer.
-  void Start();
+  // Add a single sample to this histogram.
+  void AddSample(int sample);
 
-  // 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);
+  // Is this histogram enabled?
+  // Returns false if table is full.

[Michael Starzinger, 2012/07/02 21:09:56]

Let's turn that into just one line: "Returns true if this histogram is enabled."

[jochen (gone - plz use gerrit), 2012/07/13 09:48:08]

Done.

+  bool Enabled() {
+    return GetHistogram() != NULL;
   }
 
  protected:
@@ -234,6 +236,26 @@ struct HistogramTimer {
   void* CreateHistogram() const;
 };
 
+// A HistogramTimer allows distributions of results to be created
+// HistogramTimer t = { {L"foo", 0, 10000, 50, NULL, false}, 0, 0 };
+struct HistogramTimer {
+  Histogram histogram_;
+
+  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_.Enabled() && (start_time_ != 0) && (stop_time_ == 0);
+  }
+};
+
 // Helper class for scoping a HistogramTimer.
 class HistogramTimerScope BASE_EMBEDDED {
  public: