Collect information about failing histogram factory calls.

base/metrics/histogram.cc

 // 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).
 // See header file for details and examples.
 
 #include "base/metrics/histogram.h"
@@ skipping 136 matching lines @@
 };
 
 HistogramBase* Histogram::Factory::Build() {
   // Import histograms from known persistent storage. Histograms could have
   // been added by other processes and they must be fetched and recognized
   // locally in order to be found by FindHistograms() below. If the persistent
   // memory segment is not shared between processes, this call does nothing.
   ImportPersistentHistograms();
 
   HistogramBase* histogram = StatisticsRecorder::FindHistogram(name_);
+
+  // crbug.com/588946 debugging. See comment at end of function.
+  const BucketRanges* created_ranges;

[Alexei Svitkine (slow), 2016/02/26 19:12:50]

Please initialize these to nullptr or something, else these will have garbage
values if the if below doesn't run.

[bcwhite, 2016/02/26 20:31:18]

Done.

+  const BucketRanges* registered_ranges;
+  PersistentMemoryAllocator::Reference histogram_ref;
+  HistogramBase* tentative_histogram;
+  PersistentMemoryAllocator* allocator;
+
   if (!histogram) {
     // To avoid racy destruction at shutdown, the following will be leaked.
-    const BucketRanges* created_ranges = CreateRanges();
-    const BucketRanges* registered_ranges =
+    created_ranges = CreateRanges();
+    registered_ranges =
         StatisticsRecorder::RegisterOrDeleteDuplicateRanges(created_ranges);
 
     // In most cases, the bucket-count, minimum, and maximum values are known
     // when the code is written and so are passed in explicitly. In other
     // cases (such as with a CustomHistogram), they are calculated dynamically
     // at run-time. In the latter case, those ctor parameters are zero and
     // the results extracted from the result of CreateRanges().
     if (bucket_count_ == 0) {
       bucket_count_ = static_cast<uint32_t>(registered_ranges->bucket_count());
       minimum_ = registered_ranges->range(1);
       maximum_ = registered_ranges->range(bucket_count_ - 1);
     }
 
     // Try to create the histogram using a "persistent" allocator. As of
     // 2015-01-14, the availability of such is controlled by a base::Feature
     // that is off by default. If the allocator doesn't exist or if
     // allocating from it fails, code below will allocate the histogram from
     // the process heap.
-    PersistentMemoryAllocator::Reference histogram_ref = 0;
-    HistogramBase* tentative_histogram = nullptr;
-    PersistentMemoryAllocator* allocator =
+    histogram_ref = 0;
+    tentative_histogram = nullptr;
+    allocator =
         GetPersistentHistogramMemoryAllocator();
     if (allocator) {
       flags_ |= HistogramBase::kIsPersistent;
       tentative_histogram = AllocatePersistentHistogram(
           allocator,
           histogram_type_,
           name_,
           minimum_,
           maximum_,
           registered_ranges,
@@ skipping 24 matching lines @@
   DCHECK_EQ(histogram_type_, histogram->GetHistogramType());
   if (bucket_count_ != 0 &&
       !histogram->HasConstructionArguments(minimum_, maximum_, bucket_count_)) {
     // The construction arguments do not match the existing histogram.  This can
     // come about if an extension updates in the middle of a chrome run and has
     // changed one of them, or simply by bad code within Chrome itself.  We
     // return NULL here with the expectation that bad code in Chrome will crash
     // on dereference, but extension/Pepper APIs will guard against NULL and not
     // crash.
     DLOG(ERROR) << "Histogram " << name_ << " has bad construction arguments";
-    return nullptr;
+    histogram = nullptr;
   }
+
+#if !DCHECK_IS_ON()  // Don't affect tests, only release builds.
+  // For the moment, crash here so that collected crash reports have access
+  // to the construction values in order to figure out why this is failing.
+  // TODO(bcwhite): Remove this once crbug.com/588946 is resolved. Also remove
+  // from beta-branch because we don't want crashes due to misbehaving
+  // extensions (see comment above).
+  if (!histogram) {
+    HistogramType histogram_type = histogram_type_;
+    HistogramBase::Sample minimum = minimum_;
+    HistogramBase::Sample maximum = maximum_;
+    uint32_t bucket_count = bucket_count_;
+    int32_t flags = flags_;
+    CHECK(histogram);
+    base::debug::Alias(&histogram_type);
+    base::debug::Alias(&minimum);
+    base::debug::Alias(&maximum);
+    base::debug::Alias(&bucket_count);
+    base::debug::Alias(&flags);
+    base::debug::Alias(&created_ranges);
+    base::debug::Alias(&registered_ranges);
+    base::debug::Alias(&histogram_ref);
+    base::debug::Alias(&tentative_histogram);
+    base::debug::Alias(&allocator);
+    base::debug::Alias(&tentative_histogram);
+  }
+#endif
+
   return histogram;
 }
 
 HistogramBase* Histogram::FactoryGet(const std::string& name,
                                      Sample minimum,
                                      Sample maximum,
                                      uint32_t bucket_count,
                                      int32_t flags) {
   bool valid_arguments =
       InspectConstructionArguments(name, &minimum, &maximum, &bucket_count);
@@ skipping 917 matching lines @@
     Sample sample = custom_ranges[i];
     if (sample < 0 || sample > HistogramBase::kSampleType_MAX - 1)
       return false;
     if (sample != 0)
       has_valid_range = true;
   }
   return has_valid_range;
 }
 
 }  // namespace base