124 lines
4.8 KiB
C++
124 lines
4.8 KiB
C++
// Copyright (c) 2014 Marshall A. Greenblatt. Portions copyright (c) 2011
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// Google Inc. All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the name Chromium Embedded
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// Framework nor the names of its contributors may be used to endorse
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// or promote products derived from this software without specific prior
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// written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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// This is a low level implementation of atomic semantics for reference
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// counting. Please use cef_ref_counted.h directly instead.
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//
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// The Chromium implementation includes annotations to avoid some false
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// positives when using data race detection tools. Annotations are not
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// currently supported by the CEF implementation.
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#ifndef CEF_INCLUDE_BASE_CEF_ATOMIC_REF_COUNT_H_
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#define CEF_INCLUDE_BASE_CEF_ATOMIC_REF_COUNT_H_
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#pragma once
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#if defined(USING_CHROMIUM_INCLUDES)
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// When building CEF include the Chromium header directly.
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#include "base/atomic_ref_count.h"
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#else // !USING_CHROMIUM_INCLUDES
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// The following is substantially similar to the Chromium implementation.
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// If the Chromium implementation diverges the below implementation should be
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// updated to match.
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#include <atomic>
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namespace base {
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class AtomicRefCount {
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public:
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constexpr AtomicRefCount() : ref_count_(0) {}
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explicit constexpr AtomicRefCount(int initial_value)
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: ref_count_(initial_value) {}
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///
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/// Increment a reference count.
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/// Returns the previous value of the count.
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///
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int Increment() { return Increment(1); }
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///
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/// Increment a reference count by "increment", which must exceed 0.
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/// Returns the previous value of the count.
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///
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int Increment(int increment) {
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return ref_count_.fetch_add(increment, std::memory_order_relaxed);
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}
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///
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/// Decrement a reference count, and return whether the result is non-zero.
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/// Insert barriers to ensure that state written before the reference count
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/// became zero will be visible to a thread that has just made the count zero.
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///
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bool Decrement() {
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// TODO(jbroman): Technically this doesn't need to be an acquire operation
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// unless the result is 1 (i.e., the ref count did indeed reach zero).
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// However, there are toolchain issues that make that not work as well at
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// present (notably TSAN doesn't like it).
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return ref_count_.fetch_sub(1, std::memory_order_acq_rel) != 1;
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}
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///
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/// Return whether the reference count is one. If the reference count is used
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/// in the conventional way, a refrerence count of 1 implies that the current
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/// thread owns the reference and no other thread shares it. This call
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/// performs the test for a reference count of one, and performs the memory
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/// barrier needed for the owning thread to act on the object, knowing that it
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/// has exclusive access to the object.
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///
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bool IsOne() const { return ref_count_.load(std::memory_order_acquire) == 1; }
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///
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/// Return whether the reference count is zero. With conventional object
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/// referencing counting, the object will be destroyed, so the reference count
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/// should never be zero. Hence this is generally used for a debug check.
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///
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bool IsZero() const {
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return ref_count_.load(std::memory_order_acquire) == 0;
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}
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///
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/// Returns the current reference count (with no barriers). This is subtle,
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/// and should be used only for debugging.
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///
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int SubtleRefCountForDebug() const {
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return ref_count_.load(std::memory_order_relaxed);
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}
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private:
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std::atomic_int ref_count_;
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};
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} // namespace base
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#endif // !USING_CHROMIUM_INCLUDES
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#endif // CEF_INCLUDE_BASE_CEF_ATOMIC_REF_COUNT_H_
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