Delay PersistentHistogramAllocator creation until it's known to be used.

base/metrics/persistent_histogram_allocator.cc

 // Copyright 2016 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.
 
 #include "base/metrics/persistent_histogram_allocator.h"
 
 #include <memory>
 
 #include "base/files/important_file_writer.h"
 #include "base/lazy_instance.h"
@@ skipping 29 matching lines @@
   kTypeIdCountsArray = 0x53215530 + 1,  // SHA1(CountsArray) v1
 };
 
 // The current globally-active persistent allocator for all new histograms.
 // The object held here will obviously not be destructed at process exit
 // but that's best since PersistentMemoryAllocator objects (that underlie
 // GlobalHistogramAllocator objects) are explicitly forbidden from doing
 // anything essential at exit anyway due to the fact that they depend on data
 // managed elsewhere and which could be destructed first.
 GlobalHistogramAllocator* g_allocator = nullptr;
-bool g_allocator_enabled = false;
 
 // Take an array of range boundaries and create a proper BucketRanges object
 // which is returned to the caller. A return of nullptr indicates that the
 // passed boundaries are invalid.
 std::unique_ptr<BucketRanges> CreateRangesFromData(
     HistogramBase::Sample* ranges_data,
     uint32_t ranges_checksum,
     size_t count) {
   // To avoid racy destruction at shutdown, the following may be leaked.
   std::unique_ptr<BucketRanges> ranges(new BucketRanges(count));
@@ skipping 589 matching lines @@
     NOTREACHED();
     return;
   }
 
   Set(WrapUnique(new GlobalHistogramAllocator(
       WrapUnique(new SharedPersistentMemoryAllocator(
           std::move(shm), 0, StringPiece(), /*readonly=*/false)))));
 }
 
 // static
-void GlobalHistogramAllocator::Enable() {
-  DCHECK(g_allocator);
-  g_allocator_enabled = true;
-}
-
-// static
-void GlobalHistogramAllocator::Disable() {
-  DCHECK(g_allocator);
-  g_allocator_enabled = false;
-}
-
-// static
 void GlobalHistogramAllocator::Set(
     std::unique_ptr<GlobalHistogramAllocator> allocator) {
   // Releasing or changing an allocator is extremely dangerous because it
   // likely has histograms stored within it. If the backing memory is also
   // also released, future accesses to those histograms will seg-fault.
   CHECK(!g_allocator);
   g_allocator = allocator.release();
-  g_allocator_enabled = true;
   size_t existing = StatisticsRecorder::GetHistogramCount();
 
   DVLOG_IF(1, existing)
       << existing << " histograms were created before persistence was enabled.";
 }
 
 // static
 GlobalHistogramAllocator* GlobalHistogramAllocator::Get() {
-  return g_allocator_enabled ? g_allocator : nullptr;
-}
-
-// static
-GlobalHistogramAllocator* GlobalHistogramAllocator::GetEvenIfDisabled() {
   return g_allocator;
 }
 
 // static
 std::unique_ptr<GlobalHistogramAllocator>
 GlobalHistogramAllocator::ReleaseForTesting() {
   GlobalHistogramAllocator* histogram_allocator = g_allocator;
   if (!histogram_allocator)
     return nullptr;
   PersistentMemoryAllocator* memory_allocator =
@@ skipping 23 matching lines @@
 
   g_allocator = nullptr;
   return WrapUnique(histogram_allocator);
 };
 
 void GlobalHistogramAllocator::SetPersistentLocation(const FilePath& location) {
   persistent_location_ = location;
 }
 
 bool GlobalHistogramAllocator::WriteToPersistentLocation() {
-  DCHECK(g_allocator_enabled);
-
 #if defined(OS_NACL)
   // NACL doesn't support file operations, including ImportantFileWriter.
   NOTREACHED();
   return false;
 #else
   // Stop if no destination is set.
   if (persistent_location_.empty()) {
     NOTREACHED() << "Could not write \"" << Name() << "\" persistent histograms"
                  << " to file because no location was set.";
     return false;
@@ skipping 31 matching lines @@
   while (true) {
     std::unique_ptr<HistogramBase> histogram =
         import_iterator_.GetNextWithIgnore(record_to_ignore);
     if (!histogram)
       break;
     StatisticsRecorder::RegisterOrDeleteDuplicate(histogram.release());
   }
 }
 
 }  // namespace base