diff options
Diffstat (limited to 'src/corelib/thread/qatomic_cxx11.h')
| -rw-r--r-- | src/corelib/thread/qatomic_cxx11.h | 63 |
1 files changed, 21 insertions, 42 deletions
diff --git a/src/corelib/thread/qatomic_cxx11.h b/src/corelib/thread/qatomic_cxx11.h index bf487bbf1f..47a7bc9a10 100644 --- a/src/corelib/thread/qatomic_cxx11.h +++ b/src/corelib/thread/qatomic_cxx11.h @@ -1,47 +1,12 @@ -/**************************************************************************** -** -** Copyright (C) 2011 Thiago Macieira <thiago@kde.org> -** Copyright (C) 2016 Intel Corporation. -** Contact: https://www.qt.io/licensing/ -** -** This file is part of the QtCore module of the Qt Toolkit. -** -** $QT_BEGIN_LICENSE:LGPL$ -** Commercial License Usage -** Licensees holding valid commercial Qt licenses may use this file in -** accordance with the commercial license agreement provided with the -** Software or, alternatively, in accordance with the terms contained in -** a written agreement between you and The Qt Company. For licensing terms -** and conditions see https://www.qt.io/terms-conditions. For further -** information use the contact form at https://www.qt.io/contact-us. -** -** GNU Lesser General Public License Usage -** Alternatively, this file may be used under the terms of the GNU Lesser -** General Public License version 3 as published by the Free Software -** Foundation and appearing in the file LICENSE.LGPL3 included in the -** packaging of this file. Please review the following information to -** ensure the GNU Lesser General Public License version 3 requirements -** will be met: https://www.gnu.org/licenses/lgpl-3.0.html. -** -** GNU General Public License Usage -** Alternatively, this file may be used under the terms of the GNU -** General Public License version 2.0 or (at your option) the GNU General -** Public license version 3 or any later version approved by the KDE Free -** Qt Foundation. The licenses are as published by the Free Software -** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3 -** included in the packaging of this file. Please review the following -** information to ensure the GNU General Public License requirements will -** be met: https://www.gnu.org/licenses/gpl-2.0.html and -** https://www.gnu.org/licenses/gpl-3.0.html. -** -** $QT_END_LICENSE$ -** -****************************************************************************/ +// Copyright (C) 2011 Thiago Macieira <thiago@kde.org> +// Copyright (C) 2016 Intel Corporation. +// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only #ifndef QATOMIC_CXX11_H #define QATOMIC_CXX11_H #include <QtCore/qgenericatomic.h> +#include <QtCore/qyieldcpu.h> #include <atomic> QT_BEGIN_NAMESPACE @@ -185,7 +150,7 @@ template <> inline bool QAtomicTraits<2>::isLockFree() { return false; } #endif -#if QT_CONFIG(std_atomic64) +#if !defined(QT_BOOTSTRAPPED) && QT_CONFIG(std_atomic64) template<> struct QAtomicOpsSupport<8> { enum { IsSupported = 1 }; }; # define Q_ATOMIC_INT64_IS_SUPPORTED # if ATOMIC_LLONG_LOCK_FREE == 2 @@ -278,13 +243,27 @@ template <typename X> struct QAtomicOps template <typename T> static inline bool ref(std::atomic<T> &_q_value) { - return ++_q_value != 0; + /* Conceptually, we want to + * return ++_q_value != 0; + * However, that would be sequentially consistent, and thus stronger + * than what we need. Based on + * http://eel.is/c++draft/atomics.types.memop#6, we know that + * pre-increment is equivalent to fetch_add(1) + 1. Unlike + * pre-increment, fetch_add takes a memory order argument, so we can get + * the desired acquire-release semantics. + * One last gotcha is that fetch_add(1) + 1 would need to be converted + * back to T, because it's susceptible to integer promotion. To sidestep + * this issue and to avoid UB on signed overflow, we rewrite the + * expression to: + */ + return _q_value.fetch_add(1, std::memory_order_acq_rel) != T(-1); } template <typename T> static inline bool deref(std::atomic<T> &_q_value) noexcept { - return --_q_value != 0; + // compare with ref + return _q_value.fetch_sub(1, std::memory_order_acq_rel) != T(1); } static inline bool isTestAndSetNative() noexcept |