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       1             : /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
       2             : /* This Source Code Form is subject to the terms of the Mozilla Public
       3             :  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
       4             :  * You can obtain one at http://mozilla.org/MPL/2.0/. */
       5             : 
       6             : #ifndef MOZILLA_SHAREDBUFFER_H_
       7             : #define MOZILLA_SHAREDBUFFER_H_
       8             : 
       9             : #include "mozilla/CheckedInt.h"
      10             : #include "mozilla/mozalloc.h"
      11             : #include "nsCOMPtr.h"
      12             : 
      13             : namespace mozilla {
      14             : 
      15             : class AudioBlockBuffer;
      16             : 
      17             : /**
      18             :  * Base class for objects with a thread-safe refcount and a virtual
      19             :  * destructor.
      20             :  */
      21           0 : class ThreadSharedObject {
      22             : public:
      23           0 :   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadSharedObject)
      24             : 
      25           0 :   bool IsShared() { return mRefCnt.get() > 1; }
      26             : 
      27           0 :   virtual AudioBlockBuffer* AsAudioBlockBuffer() { return nullptr; };
      28             : 
      29           0 :   virtual size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
      30             :   {
      31           0 :     return 0;
      32             :   }
      33             : 
      34           0 :   virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
      35             :   {
      36           0 :     return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
      37             :   }
      38             : protected:
      39             :   // Protected destructor, to discourage deletion outside of Release():
      40           0 :   virtual ~ThreadSharedObject() {}
      41             : };
      42             : 
      43             : /**
      44             :  * Heap-allocated chunk of arbitrary data with threadsafe refcounting.
      45             :  * Typically you would allocate one of these, fill it in, and then treat it as
      46             :  * immutable while it's shared.
      47             :  * This only guarantees 4-byte alignment of the data. For alignment we simply
      48             :  * assume that the memory from malloc is at least 4-byte aligned and the
      49             :  * refcount's size is large enough that SharedBuffer's size is divisible by 4.
      50             :  */
      51           0 : class SharedBuffer : public ThreadSharedObject {
      52             : public:
      53           0 :   void* Data() { return this + 1; }
      54             : 
      55           0 :   static already_AddRefed<SharedBuffer> Create(size_t aSize)
      56             :   {
      57           0 :     CheckedInt<size_t> size = sizeof(SharedBuffer);
      58           0 :     size += aSize;
      59           0 :     if (!size.isValid()) {
      60           0 :       MOZ_CRASH();
      61             :     }
      62           0 :     void* m = moz_xmalloc(size.value());
      63           0 :     RefPtr<SharedBuffer> p = new (m) SharedBuffer();
      64           0 :     NS_ASSERTION((reinterpret_cast<char*>(p.get() + 1) - reinterpret_cast<char*>(p.get())) % 4 == 0,
      65             :                  "SharedBuffers should be at least 4-byte aligned");
      66           0 :     return p.forget();
      67             :   }
      68             : 
      69           0 :   size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const override
      70             :   {
      71           0 :     return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
      72             :   }
      73             : 
      74             : private:
      75           0 :   SharedBuffer() {}
      76             : };
      77             : 
      78             : } // namespace mozilla
      79             : 
      80             : #endif /* MOZILLA_SHAREDBUFFER_H_ */