Use lock-free lazy initialization for static histogram references

net/disk_cache/stats.cc

-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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 "net/disk_cache/stats.h"
 
 #include "base/format_macros.h"
 #include "base/logging.h"
 #include "base/string_util.h"
 #include "base/stringprintf.h"
 #include "net/disk_cache/backend_impl.h"
@@ skipping 97 matching lines @@
   // If we have more than 512 bytes of counters, change kDiskSignature so we
   // don't overwrite something else (LoadStats must fail).
   COMPILE_ASSERT(sizeof(*stats) <= 256 * 2, use_more_blocks);
   memset(stats, 0, sizeof(*stats));
   stats->signature = kDiskSignature;
   stats->size = sizeof(*stats);
 
   return StoreStats(backend, *address, stats);
 }
 
-Stats::Stats() : backend_(NULL) {
+Stats::Stats() : backend_(NULL), size_histogram_(NULL) {
 }
 
 Stats::~Stats() {
 }
 
 bool Stats::Init(BackendImpl* backend, uint32* storage_addr) {
   OnDiskStats stats;
   Addr address(*storage_addr);
   if (address.is_initialized()) {
     if (!LoadStats(backend, address, &stats))
       return false;
   } else {
     if (!CreateStats(backend, &address, &stats))
       return false;
     *storage_addr = address.value();
   }
 
   storage_addr_ = address.value();
   backend_ = backend;
 
   memcpy(data_sizes_, stats.data_sizes, sizeof(data_sizes_));
   memcpy(counters_, stats.counters, sizeof(counters_));
 
   // It seems impossible to support this histogram for more than one
   // simultaneous objects with the current infrastructure.
   static bool first_time = true;
   if (first_time) {
     first_time = false;
     // ShouldReportAgain() will re-enter this object.
-    if (!size_histogram_.get() && backend->cache_type() == net::DISK_CACHE &&
+    if (!size_histogram_ && backend->cache_type() == net::DISK_CACHE &&
         backend->ShouldReportAgain()) {
       // Stats may be reused when the cache is re-created, but we want only one
       // histogram at any given time.
       size_histogram_ =
           StatsHistogram::StatsHistogramFactoryGet("DiskCache.SizeStats");
       size_histogram_->Init(this);
     }
   }
 
   return true;
@@ skipping 160 matching lines @@
 int Stats::GetRatio(Counters hit, Counters miss) const {
   int64 ratio = GetCounter(hit) * 100;
   if (!ratio)
     return 0;
 
   ratio /= (GetCounter(hit) + GetCounter(miss));
   return static_cast<int>(ratio);
 }
 
 }  // namespace disk_cache