michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
michael@0:  * You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef MOZILLA_SHAREDBUFFER_H_
michael@0: #define MOZILLA_SHAREDBUFFER_H_
michael@0: 
michael@0: #include "mozilla/CheckedInt.h"
michael@0: #include "mozilla/mozalloc.h"
michael@0: #include "nsCOMPtr.h"
michael@0: #include "nsAutoPtr.h"
michael@0: 
michael@0: namespace mozilla {
michael@0: 
michael@0: /**
michael@0:  * Base class for objects with a thread-safe refcount and a virtual
michael@0:  * destructor.
michael@0:  */
michael@0: class ThreadSharedObject {
michael@0: public:
michael@0:   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadSharedObject)
michael@0: 
michael@0:   bool IsShared() { return mRefCnt.get() > 1; }
michael@0: 
michael@0:   virtual size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
michael@0:   {
michael@0:     return 0;
michael@0:   }
michael@0: 
michael@0:   virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
michael@0:   {
michael@0:     return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
michael@0:   }
michael@0: protected:
michael@0:   // Protected destructor, to discourage deletion outside of Release():
michael@0:   virtual ~ThreadSharedObject() {}
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * Heap-allocated chunk of arbitrary data with threadsafe refcounting.
michael@0:  * Typically you would allocate one of these, fill it in, and then treat it as
michael@0:  * immutable while it's shared.
michael@0:  * This only guarantees 4-byte alignment of the data. For alignment we
michael@0:  * simply assume that the refcount is at least 4-byte aligned and its size
michael@0:  * is divisible by 4.
michael@0:  */
michael@0: class SharedBuffer : public ThreadSharedObject {
michael@0: public:
michael@0:   void* Data() { return this + 1; }
michael@0: 
michael@0:   static already_AddRefed<SharedBuffer> Create(size_t aSize)
michael@0:   {
michael@0:     CheckedInt<size_t> size = sizeof(SharedBuffer);
michael@0:     size += aSize;
michael@0:     if (!size.isValid()) {
michael@0:       MOZ_CRASH();
michael@0:     }
michael@0:     void* m = moz_xmalloc(size.value());
michael@0:     nsRefPtr<SharedBuffer> p = new (m) SharedBuffer();
michael@0:     NS_ASSERTION((reinterpret_cast<char*>(p.get() + 1) - reinterpret_cast<char*>(p.get())) % 4 == 0,
michael@0:                  "SharedBuffers should be at least 4-byte aligned");
michael@0:     return p.forget();
michael@0:   }
michael@0: 
michael@0:   virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const MOZ_OVERRIDE
michael@0:   {
michael@0:     return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
michael@0:   }
michael@0: 
michael@0: private:
michael@0:   SharedBuffer() {}
michael@0: };
michael@0: 
michael@0: }
michael@0: 
michael@0: #endif /* MOZILLA_SHAREDBUFFER_H_ */