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86ee89f73e
On a 32bit system, this reduces the allocation size of the flag down from 12 bytes to 8, and removes the need for a vtable (the extra 4 bytes are the vtable pointer). The downside is that this change makes the binary layout of the flag, less compatible with RefCountedObject<> based reference counting objects and thus we don't immediately get the benefits of identical COMDAT folding and subsequently there's a slight binary size increase. With wider use, the binary size benefits will come. Bug: none Change-Id: I04129771790a3258d6accaf0ab1258b7a798a55e Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215681 Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org> Commit-Queue: Tommi <tommi@webrtc.org> Cr-Commit-Position: refs/heads/master@{#33793}
89 lines
2.6 KiB
C++
89 lines
2.6 KiB
C++
/*
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* Copyright 2017 The WebRTC Project Authors. All rights reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef API_REF_COUNTED_BASE_H_
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#define API_REF_COUNTED_BASE_H_
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#include <type_traits>
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#include "rtc_base/constructor_magic.h"
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#include "rtc_base/ref_counter.h"
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namespace rtc {
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class RefCountedBase {
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public:
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RefCountedBase() = default;
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void AddRef() const { ref_count_.IncRef(); }
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RefCountReleaseStatus Release() const {
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const auto status = ref_count_.DecRef();
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if (status == RefCountReleaseStatus::kDroppedLastRef) {
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delete this;
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}
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return status;
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}
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protected:
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virtual ~RefCountedBase() = default;
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private:
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mutable webrtc::webrtc_impl::RefCounter ref_count_{0};
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RTC_DISALLOW_COPY_AND_ASSIGN(RefCountedBase);
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};
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// Template based version of `RefCountedBase` for simple implementations that do
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// not need (or want) destruction via virtual destructor or the overhead of a
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// vtable.
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//
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// To use:
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// struct MyInt : public rtc::RefCountedNonVirtual<MyInt> {
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// int foo_ = 0;
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// };
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//
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// rtc::scoped_refptr<MyInt> my_int(new MyInt());
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//
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// sizeof(MyInt) on a 32 bit system would then be 8, int + refcount and no
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// vtable generated.
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template <typename T>
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class RefCountedNonVirtual {
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public:
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RefCountedNonVirtual() = default;
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void AddRef() const { ref_count_.IncRef(); }
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RefCountReleaseStatus Release() const {
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// If you run into this assert, T has virtual methods. There are two
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// options:
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// 1) The class doesn't actually need virtual methods, the type is complete
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// so the virtual attribute(s) can be removed.
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// 2) The virtual methods are a part of the design of the class. In this
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// case you can consider using `RefCountedBase` instead or alternatively
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// use `rtc::RefCountedObject`.
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static_assert(!std::is_polymorphic<T>::value,
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"T has virtual methods. RefCountedBase is a better fit.");
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const auto status = ref_count_.DecRef();
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if (status == RefCountReleaseStatus::kDroppedLastRef) {
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delete static_cast<const T*>(this);
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}
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return status;
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}
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protected:
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~RefCountedNonVirtual() = default;
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private:
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mutable webrtc::webrtc_impl::RefCounter ref_count_{0};
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RTC_DISALLOW_COPY_AND_ASSIGN(RefCountedNonVirtual);
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};
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} // namespace rtc
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#endif // API_REF_COUNTED_BASE_H_
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