Make sure there is only one instance of the stats histogram at a given time....

net/disk_cache/stats.cc

 // Copyright (c) 2006-2008 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/logging.h"
 #include "base/string_util.h"
 #include "net/disk_cache/backend_impl.h"
 
@@ skipping 56 matching lines @@
     return false;
 
   size_t offset = address.start_block() * address.BlockSize() +
                   kBlockHeaderSize;
   if (!file->Read(stats, sizeof(*stats), offset))
     return false;
 
   if (stats->signature != kDiskSignature)
     return false;
 
-  // We don't want to discard the whole cache everytime we have one extra
+  // We don't want to discard the whole cache every time we have one extra
   // counter; just reset them to zero.
   if (stats->size != sizeof(*stats))
     memset(stats, 0, sizeof(*stats));
 
   return true;
 }
 
 bool StoreStats(BackendImpl* backend, Addr address, OnDiskStats* stats) {
   MappedFile* file = backend->File(address);
   if (!file)
@@ skipping 25 matching lines @@
     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;
-  size_histogram_.reset(new StatsHistogram(L"DiskCache.SizeStats"));
-  size_histogram_->Init(this);
+  if (!size_histogram_.get()) {
+    // Stats may be reused when the cache is re-created, but we want only one
+    // histogram at any given time.
+    size_histogram_.reset(new StatsHistogram(L"DiskCache.SizeStats"));
+    size_histogram_->Init(this);
+  }
 
   memcpy(data_sizes_, stats.data_sizes, sizeof(data_sizes_));
   memcpy(counters_, stats.counters, sizeof(counters_));
 
   return true;
 }
 
 Stats::~Stats() {
   if (!backend_)
     return;
@@ skipping 122 matching lines @@
 
   for (int i = MIN_COUNTER + 1; i < MAX_COUNTER; i++) {
     item.first = kCounterNames[i];
     item.second = StringPrintf("0x%I64x", counters_[i]);
     items->push_back(item);
   }
 }
 
 }  // namespace disk_cache