The Tor Browser: content/media/SharedBuffer.h@44a2da4a2ab2

Replace accessor implementation with direct member state manipulation, by
request https://trac.torproject.org/projects/tor/ticket/9701#comment:32

     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/. */

     6 #ifndef MOZILLA_SHAREDBUFFER_H_

     7 #define MOZILLA_SHAREDBUFFER_H_

     9 #include "mozilla/CheckedInt.h"

    10 #include "mozilla/mozalloc.h"

    11 #include "nsCOMPtr.h"

    12 #include "nsAutoPtr.h"

    14 namespace mozilla {

    16 /**

    17  * Base class for objects with a thread-safe refcount and a virtual

    18  * destructor.

    19  */

    20 class ThreadSharedObject {

    21 public:

    22   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadSharedObject)

    24   bool IsShared() { return mRefCnt.get() > 1; }

    26   virtual size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const

    27   {

    28     return 0;

    29   }

    31   virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const

    32   {

    33     return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);

    34   }

    35 protected:

    36   // Protected destructor, to discourage deletion outside of Release():

    37   virtual ~ThreadSharedObject() {}

    38 };

    40 /**

    41  * Heap-allocated chunk of arbitrary data with threadsafe refcounting.

    42  * Typically you would allocate one of these, fill it in, and then treat it as

    43  * immutable while it's shared.

    44  * This only guarantees 4-byte alignment of the data. For alignment we

    45  * simply assume that the refcount is at least 4-byte aligned and its size

    46  * is divisible by 4.

    47  */

    48 class SharedBuffer : public ThreadSharedObject {

    49 public:

    50   void* Data() { return this + 1; }

    52   static already_AddRefed<SharedBuffer> Create(size_t aSize)

    53   {

    54     CheckedInt<size_t> size = sizeof(SharedBuffer);

    55     size += aSize;

    56     if (!size.isValid()) {

    57       MOZ_CRASH();

    58     }

    59     void* m = moz_xmalloc(size.value());

    60     nsRefPtr<SharedBuffer> p = new (m) SharedBuffer();

    61     NS_ASSERTION((reinterpret_cast<char*>(p.get() + 1) - reinterpret_cast<char*>(p.get())) % 4 == 0,

    62                  "SharedBuffers should be at least 4-byte aligned");

    63     return p.forget();

    64   }

    66   virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const MOZ_OVERRIDE

    67   {

    68     return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);

    69   }

    71 private:

    72   SharedBuffer() {}

    73 };

    75 }

    77 #endif /* MOZILLA_SHAREDBUFFER_H_ */

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