Return a NULL histogram pointer on construction error

base/metrics/histogram.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Histogram is an object that aggregates statistics, and can summarize them in
 // various forms, including ASCII graphical, HTML, and numerically (as a
 // vector of numbers corresponding to each of the aggregating buckets).
 
 // It supports calls to accumulate either time intervals (which are processed
 // as integral number of milliseconds), or arbitrary integral units.
@@ skipping 367 matching lines @@
   //----------------------------------------------------------------------------
   // For a valid histogram, input should follow these restrictions:
   // minimum > 0 (if a minimum below 1 is specified, it will implicitly be
   //              normalized up to 1)
   // maximum > minimum
   // buckets > 2 [minimum buckets needed: underflow, overflow and the range]
   // Additionally,
   // buckets <= (maximum - minimum + 2) - this is to ensure that we don't have
   // more buckets than the range of numbers; having more buckets than 1 per
   // value in the range would be nonsensical.
-  static HistogramBase* FactoryGet(const std::string& name,
-                                   Sample minimum,
-                                   Sample maximum,
-                                   size_t bucket_count,
-                                   int32 flags);
-  static HistogramBase* FactoryTimeGet(const std::string& name,
-                                       base::TimeDelta minimum,
-                                       base::TimeDelta maximum,
-                                       size_t bucket_count,
-                                       int32 flags);
+  static HistogramBase* FactoryGet(
+      const std::string& name,
+      Sample minimum,
+      Sample maximum,
+      size_t bucket_count,
+      int32 flags,
+      int32 construction_behavior = kDoNotAllowBadConstruction);

[jar (doing other things), 2014/01/24 16:15:09]

Sadly, this is a violation of the style guide.

Perhaps instead of using a CHECK() in the method, we can return a NULL pointer
when there is a violation.  That would then effectively CHECK (crash) if the
caller was not prepared for "bad construction".  If the caller could tolerate
bad construction, and wanted the flow to continue, then they could replace the
NULL pointer with the planned "dummy_histogram".

[elijahtaylor1, 2014/01/24 20:37:22]

If allowing NULL dereference is ok for what we're considering bad code in
Chrome, this approach makes everything much simpler.  Both the extension and
Pepper API do a FactoryGet then immediately Add, they don't keep the object
around, so we can just guard against NULL dereference there and everything
should be good.

+  static HistogramBase* FactoryTimeGet(
+      const std::string& name,
+      base::TimeDelta minimum,
+      base::TimeDelta maximum,
+      size_t bucket_count,
+      int32 flags,
+      int32 construction_behavior = kDoNotAllowBadConstruction);
 
   // Time call for use with DHISTOGRAM*.
   // Returns TimeTicks::Now() in debug and TimeTicks() in release build.
   static TimeTicks DebugNow();
 
   static void InitializeBucketRanges(Sample minimum,
                                      Sample maximum,
                                      BucketRanges* ranges);
 
   // This constant if for FindCorruption. Since snapshots of histograms are
@@ skipping 131 matching lines @@
 //------------------------------------------------------------------------------
 
 // LinearHistogram is a more traditional histogram, with evenly spaced
 // buckets.
 class BASE_EXPORT LinearHistogram : public Histogram {
  public:
   virtual ~LinearHistogram();
 
   /* 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,
-                                   Sample minimum,
-                                   Sample maximum,
-                                   size_t bucket_count,
-                                   int32 flags);
+  static HistogramBase* FactoryGet(
+      const std::string& name,
+      Sample minimum,
+      Sample maximum,
+      size_t bucket_count,
+      int32 flags,
+      int32 construction_behavior = kDoNotAllowBadConstruction);
   static HistogramBase* FactoryTimeGet(const std::string& name,
-                                       TimeDelta minimum,
-                                       TimeDelta maximum,
-                                       size_t bucket_count,
-                                       int32 flags);
+      TimeDelta minimum,
+      TimeDelta maximum,
+      size_t bucket_count,
+      int32 flags,
+      int32 construction_behavior = kDoNotAllowBadConstruction);
 
   struct DescriptionPair {
     Sample sample;
     const char* description;  // Null means end of a list of pairs.
   };
 
   // Create a LinearHistogram and store a list of number/text values for use in
   // writing the histogram graph.
   // |descriptions| can be NULL, which means no special descriptions to set. If
   // it's not NULL, the last element in the array must has a NULL in its
   // "description" field.
   static HistogramBase* FactoryGetWithRangeDescription(
       const std::string& name,
       Sample minimum,
       Sample maximum,
       size_t bucket_count,
       int32 flags,
-      const DescriptionPair descriptions[]);
+      const DescriptionPair descriptions[],
+      int32 construction_behavior = kDoNotAllowBadConstruction);
 
   static void InitializeBucketRanges(Sample minimum,
                                      Sample maximum,
                                      BucketRanges* ranges);
 
   // Overridden from Histogram:
   virtual HistogramType GetHistogramType() const OVERRIDE;
 
  protected:
   LinearHistogram(const std::string& name,
@@ skipping 85 matching lines @@
   static bool ValidateCustomRanges(const std::vector<Sample>& custom_ranges);
   static BucketRanges* CreateBucketRangesFromCustomRanges(
       const std::vector<Sample>& custom_ranges);
 
   DISALLOW_COPY_AND_ASSIGN(CustomHistogram);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_H_