Support "shared" histograms between processes.

base/metrics/histogram.h

Index: base/metrics/histogram.h
diff --git a/base/metrics/histogram.h b/base/metrics/histogram.h
index 8840493af098437104ed0ba8693e72e860360ab9..646c377ca6dc151dbbde4f36d751e944407c91ab 100644
--- a/base/metrics/histogram.h
+++ b/base/metrics/histogram.h
@@ -89,10 +89,13 @@ class BooleanHistogram;
 class CustomHistogram;
 class Histogram;
 class LinearHistogram;
+class PersistentMemoryAllocator;
 class Pickle;
 class PickleIterator;
 class SampleVector;
 
+struct PersistentHistogramData;
+
 class BASE_EXPORT Histogram : public HistogramBase {
  public:
   // Initialize maximum number of buckets in histograms as 16,384.
@@ -190,6 +193,13 @@ class BASE_EXPORT Histogram : public HistogramBase {
   void WriteAscii(std::string* output) const override;
 
  protected:
+  // This class, defined entirely within the .cc file, contains all the
+  // common logic for building a Histogram and can be overridden by more
+  // specific types to alter details of how the creation is done. It is
+  // defined as an embedded class (rather than an anonymous one) so it
+  // can access the protected constructors.
+  class Factory;
+
   // |ranges| should contain the underflow and overflow buckets. See top
   // comments for example.
   Histogram(const std::string& name,
@@ -197,6 +207,20 @@ class BASE_EXPORT Histogram : public HistogramBase {
             Sample maximum,
             const BucketRanges* ranges);
 
+  // Traditionally, histograms allocate their own memory for the bucket
+  // vector but "shared" histograms use memory regions allocated from a
+  // special memory segment that is passed in here.  It is assumed that
+  // the life of this memory is managed externally and exceeds the lifetime
+  // of this object. Practically, this memory is never released until the
+  // process exits and the OS cleans it up.
+  Histogram(const std::string& name,
+            Sample minimum,
+            Sample maximum,
+            const BucketRanges* ranges,
+            HistogramBase::AtomicCount* counts,
+            size_t counts_size,
+            HistogramSamples::Metadata* meta);
+
   ~Histogram() override;
 
   // HistogramBase implementation:
@@ -225,6 +249,9 @@ class BASE_EXPORT Histogram : public HistogramBase {
   friend class StatisticsRecorder;  // To allow it to delete duplicates.
   friend class StatisticsRecorderTest;
 
+  friend BASE_EXPORT HistogramBase* CreatePersistentHistogram(
+      PersistentMemoryAllocator* allocator,
+      PersistentHistogramData* histogram_data);
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
@@ -279,8 +306,6 @@ class BASE_EXPORT Histogram : public HistogramBase {
 // buckets.
 class BASE_EXPORT LinearHistogram : public Histogram {
  public:
-  ~LinearHistogram() override;

[Alexei Svitkine (slow), 2015/12/21 19:32:11]

Why is this removed?

Non-trivial classes should have explicit out of line destructors.

Otherwise, every file that includes the header will generate machine code for it
which has to be deduped at link time, which causes slower build times.

[bcwhite, 2015/12/22 20:50:38]

I removed it because it was the only one of the three derived classes that had
one.  I missed the BucketDescriptionMap member variable.

Restored.

-
   /* minimum should start from 1. 0 is as minimum is invalid. 0 is an implicit
      default underflow bucket. */
   static HistogramBase* FactoryGet(const std::string& name,
@@ -334,11 +359,21 @@ class BASE_EXPORT LinearHistogram : public Histogram {
   HistogramType GetHistogramType() const override;
 
  protected:
+  class Factory;
+
   LinearHistogram(const std::string& name,
                   Sample minimum,
                   Sample maximum,
                   const BucketRanges* ranges);
 
+  LinearHistogram(const std::string& name,
+                  Sample minimum,
+                  Sample maximum,
+                  const BucketRanges* ranges,
+                  HistogramBase::AtomicCount* counts,
+                  size_t counts_size,
+                  HistogramSamples::Metadata* meta);
+
   double GetBucketSize(Count current, size_t i) const override;
 
   // If we have a description for a bucket, then return that.  Otherwise
@@ -350,6 +385,9 @@ class BASE_EXPORT LinearHistogram : public Histogram {
   bool PrintEmptyBucket(size_t index) const override;
 
  private:
+  friend BASE_EXPORT HistogramBase* CreatePersistentHistogram(
+      PersistentMemoryAllocator* allocator,
+      PersistentHistogramData* histogram_data);
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
@@ -377,9 +415,19 @@ class BASE_EXPORT BooleanHistogram : public LinearHistogram {
 
   HistogramType GetHistogramType() const override;
 
+ protected:
+  class Factory;
+
  private:
   BooleanHistogram(const std::string& name, const BucketRanges* ranges);
-
+  BooleanHistogram(const std::string& name,
+                   const BucketRanges* ranges,
+                   HistogramBase::AtomicCount* counts,
+                   HistogramSamples::Metadata* meta);
+
+  friend BASE_EXPORT HistogramBase* CreatePersistentHistogram(
+      PersistentMemoryAllocator* allocator,
+      PersistentHistogramData* histogram_data);
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
@@ -419,22 +467,31 @@ class BASE_EXPORT CustomHistogram : public Histogram {
   static std::vector<Sample> ArrayToCustomRanges(const Sample* values,
                                                  size_t num_values);
  protected:
+  class Factory;
+
   CustomHistogram(const std::string& name,
                   const BucketRanges* ranges);
 
+  CustomHistogram(const std::string& name,
+                  const BucketRanges* ranges,
+                  HistogramBase::AtomicCount* counts,
+                  size_t counts_size,
+                  HistogramSamples::Metadata* meta);
+
   // HistogramBase implementation:
   bool SerializeInfoImpl(base::Pickle* pickle) const override;
 
   double GetBucketSize(Count current, size_t i) const override;
 
  private:
+  friend BASE_EXPORT HistogramBase* CreatePersistentHistogram(
+      PersistentMemoryAllocator* allocator,
+      PersistentHistogramData* histogram_data);
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
 
   static bool ValidateCustomRanges(const std::vector<Sample>& custom_ranges);
-  static BucketRanges* CreateBucketRangesFromCustomRanges(
-      const std::vector<Sample>& custom_ranges);
 
   DISALLOW_COPY_AND_ASSIGN(CustomHistogram);
 };