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..608a30d96df05211fc1a237cc8b3dde0f045fa13 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 +193,22 @@ class BASE_EXPORT Histogram : public HistogramBase {
   void WriteAscii(std::string* output) const override;
 
  protected:
+  // This is the basis of all FactoryGet methods, parameterized with three
+  // histogram-type-specific blocks of code to create the ranges, perform
+  // allocation from the heap, and do any post-construction datafill. If
+  // the min/max/count is not known in advance (i.e. it's determined
+  // dynamically in |create_ranges|), pass zero (0) for all three.
+  static HistogramBase* Histogram::FactoryGet(
+    std::function<BucketRanges*()> create_ranges,
+    std::function<HistogramBase*(const BucketRanges*)> heap_alloc,
+    std::function<void(HistogramBase*)> fill_histogram,
+    HistogramType histogram_type,
+    const std::string& name,
+    Sample minimum,
+    Sample maximum,
+    size_t bucket_count,
+    int32 flags);
+
   // |ranges| should contain the underflow and overflow buckets. See top
   // comments for example.
   Histogram(const std::string& name,
@@ -197,6 +216,20 @@ 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 +258,9 @@ 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);
@@ -339,6 +375,14 @@ class BASE_EXPORT LinearHistogram : public Histogram {
                   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 +394,9 @@ 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);
@@ -379,7 +426,14 @@ class BASE_EXPORT BooleanHistogram : public LinearHistogram {
 
  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);
@@ -422,19 +476,26 @@ class BASE_EXPORT CustomHistogram : public Histogram {
   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);
 };