Restrict volatile section of block header.

base/metrics/persistent_memory_allocator.h

 // Copyright (c) 2015 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.
 
 #ifndef BASE_METRICS_PERSISTENT_MEMORY_ALLOCATOR_H_
 #define BASE_METRICS_PERSISTENT_MEMORY_ALLOCATOR_H_
 
 #include <stdint.h>
 #include <atomic>
 #include <string>
@@ skipping 231 matching lines @@
  private:
   struct SharedMetadata;
   struct BlockHeader;
   static const uint32_t kAllocAlignment;
   static const Reference kReferenceQueue;
   static const Reference kReferenceNull;
 
   // The shared metadata is always located at the top of the memory segment.
   // These convenience functions eliminate constant casting of the base
   // pointer within the code.
-  const volatile SharedMetadata* shared_meta() const {
-    return reinterpret_cast<const volatile SharedMetadata*>(mem_base_);
+  const SharedMetadata* shared_meta() const {
+    return reinterpret_cast<const SharedMetadata*>(
+        const_cast<const char*>(mem_base_));

[Alexei Svitkine (slow), 2016/02/05 19:31:32]

I don't understand why there's a const_cast here?

   }
-  volatile SharedMetadata* shared_meta() {
-    return reinterpret_cast<volatile SharedMetadata*>(mem_base_);
+  SharedMetadata* shared_meta() {
+    return reinterpret_cast<SharedMetadata*>(const_cast<char*>(mem_base_));
   }
 
   // Actual method for doing the allocation.
   Reference AllocateImpl(size_t size, uint32_t type_id);
 
   // Get the block header associated with a specific reference.
   const volatile BlockHeader* GetBlock(Reference ref, uint32_t type_id,
                                        uint32_t size, bool queue_ok,
                                        bool free_ok) const;
   volatile BlockHeader* GetBlock(Reference ref, uint32_t type_id, uint32_t size,
@@ skipping 57 matching lines @@
   // the rest.
   static bool IsFileAcceptable(const MemoryMappedFile& file);
 
  private:
   scoped_ptr<MemoryMappedFile> mapped_file_;
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_PERSISTENT_MEMORY_ALLOCATOR_H_