Add SharedMemory version of PersistentMemoryAllocator.

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>
 
 #include "base/atomicops.h"
 #include "base/base_export.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
 
 class HistogramBase;
 class MemoryMappedFile;
+class SharedMemory;
 
 // Simple allocator for pieces of a memory block that may be persistent
 // to some storage or shared across multiple processes. This class resides
 // under base/metrics because it was written for that purpose. It is,
 // however, fully general-purpose and can be freely moved to base/memory
 // if other uses are found.
 //
 // This class provides for thread-secure (i.e. safe against other threads
 // or processes that may be compromised and thus have malicious intent)
 // allocation of memory within a designated block and also a mechanism by
@@ skipping 269 matching lines @@
  public:
   LocalPersistentMemoryAllocator(size_t size, uint64_t id,
                                  const std::string& name);
   ~LocalPersistentMemoryAllocator() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LocalPersistentMemoryAllocator);
 };
 
 
+// This allocator takes a shared-memory object and performs allocation from
+// it. The memory must be previously mapped via Map() or MapAt(). The allocator
+// takes ownership of the memory object.
+class BASE_EXPORT SharedPersistentMemoryAllocator
+    : public PersistentMemoryAllocator {
+ public:
+  SharedPersistentMemoryAllocator(scoped_ptr<SharedMemory> memory, uint64_t id,
+                                  const std::string& name, bool read_only);
+  ~SharedPersistentMemoryAllocator() override;
+
+  SharedMemory* shared_memory() { return shared_memory_.get(); }
+
+  // Ensure that the memory isn't so invalid that it won't crash when passing it
+  // to the allocator. This doesn't guarantee the data is valid, just that it
+  // won't cause the program to abort. The existing IsCorrupt() call will handle
+  // the rest.
+  static bool IsSharedMemoryAcceptable(const SharedMemory& memory);

[Alexei Svitkine (slow), 2016/02/09 19:58:44]

I understand why you don't want to use IsValid() but I find "Acceptable" very
vague and hard to understand without reading the comment.

But looking at the impl, I guess you use "Acceptable" already elsewhere, so I
guess it should be consistent. But I would have suggesting something like
"SanityCheckSharedMemory()" or some other wording that's more precise than
"Acceptable".

[bcwhite, 2016/02/10 16:43:53]

Acknowledged.

+
+ private:
+  scoped_ptr<SharedMemory> shared_memory_;
+  DISALLOW_COPY_AND_ASSIGN(SharedPersistentMemoryAllocator);
+};
+
+
 // This allocator takes a memory-mapped file object and performs allocation
 // from it. The allocator takes ownership of the file object. Only read access
 // is provided due to limitions of the MemoryMappedFile class.
 class BASE_EXPORT FilePersistentMemoryAllocator
     : public PersistentMemoryAllocator {
  public:
-  FilePersistentMemoryAllocator(MemoryMappedFile* file, uint64_t id,
+  FilePersistentMemoryAllocator(scoped_ptr<MemoryMappedFile> file, uint64_t id,
                                 const std::string& name);
   ~FilePersistentMemoryAllocator() override;
 
   // Ensure that the file isn't so invalid that it won't crash when passing it
   // to the allocator. This doesn't guarantee the file is valid, just that it
-  // won't cause program to abort. The existing IsCorrupt() call will handle
+  // won't cause the program to abort. The existing IsCorrupt() call will handle
   // the rest.
   static bool IsFileAcceptable(const MemoryMappedFile& file);
 
  private:
   scoped_ptr<MemoryMappedFile> mapped_file_;
+  DISALLOW_COPY_AND_ASSIGN(FilePersistentMemoryAllocator);

[Alexei Svitkine (slow), 2016/02/09 19:58:44]

Nit: Put an empty line above these lines.

[bcwhite, 2016/02/10 16:43:53]

Done.

 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_PERSISTENT_MEMORY_ALLOCATOR_H_