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Diffstat (limited to 'src/corelib/thread/qmutex_linux.cpp')
| -rw-r--r-- | src/corelib/thread/qmutex_linux.cpp | 182 |
1 files changed, 0 insertions, 182 deletions
diff --git a/src/corelib/thread/qmutex_linux.cpp b/src/corelib/thread/qmutex_linux.cpp deleted file mode 100644 index 72002838cf..0000000000 --- a/src/corelib/thread/qmutex_linux.cpp +++ /dev/null @@ -1,182 +0,0 @@ -/**************************************************************************** -** -** Copyright (C) 2016 The Qt Company Ltd. -** 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. -** -** $QT_END_LICENSE$ -** -****************************************************************************/ - -#include "qplatformdefs.h" -#include "qmutex.h" -#include "qatomic.h" -#include "qmutex_p.h" -#include "qfutex_p.h" - -#ifndef QT_ALWAYS_USE_FUTEX -# error "Qt build is broken: qmutex_linux.cpp is being built but futex support is not wanted" -#endif - -#ifndef FUTEX_PRIVATE_FLAG -# define FUTEX_PRIVATE_FLAG 0 -#endif - -QT_BEGIN_NAMESPACE - -using namespace QtFutex; - -/* - * QBasicMutex implementation on Linux with futexes - * - * QBasicMutex contains one pointer value, which can contain one of four - * different values: - * 0x0 unlocked, non-recursive mutex - * 0x1 locked non-recursive mutex, no waiters - * 0x3 locked non-recursive mutex, at least one waiter - * > 0x3 recursive mutex, points to a QMutexPrivate object - * - * LOCKING (non-recursive): - * - * A non-recursive mutex starts in the 0x0 state, indicating that it's - * unlocked. When the first thread attempts to lock it, it will perform a - * testAndSetAcquire from 0x0 to 0x1. If that succeeds, the caller concludes - * that it successfully locked the mutex. That happens in fastTryLock(). - * - * If that testAndSetAcquire fails, QBasicMutex::lockInternal is called. - * - * lockInternal will examine the value of the pointer. Otherwise, it will use - * futexes to sleep and wait for another thread to unlock. To do that, it needs - * to set a pointer value of 0x3, which indicates that thread is waiting. It - * does that by a simple fetchAndStoreAcquire operation. - * - * If the pointer value was 0x0, it means we succeeded in acquiring the mutex. - * For other values, it will then call FUTEX_WAIT and with an expected value of - * 0x3. - * - * If the pointer value changed before futex(2) managed to sleep, it will - * return -1 / EWOULDBLOCK, in which case we have to start over. And even if we - * are woken up directly by a FUTEX_WAKE, we need to acquire the mutex, so we - * start over again. - * - * UNLOCKING (non-recursive): - * - * To unlock, we need to set a value of 0x0 to indicate it's unlocked. The - * first attempt is a testAndSetRelease operation from 0x1 to 0x0. If that - * succeeds, we're done. - * - * If it fails, unlockInternal() is called. The only possibility is that the - * mutex value was 0x3, which indicates some other thread is waiting or was - * waiting in the past. We then set the mutex to 0x0 and perform a FUTEX_WAKE. - */ - -static inline QMutexData *dummyFutexValue() -{ - return reinterpret_cast<QMutexData *>(quintptr(3)); -} - -template <bool IsTimed> static inline -bool lockInternal_helper(QBasicAtomicPointer<QMutexData> &d_ptr, int timeout = -1, QElapsedTimer *elapsedTimer = nullptr) noexcept -{ - if (!IsTimed) - timeout = -1; - - // we're here because fastTryLock() has just failed - if (timeout == 0) - return false; - - // the mutex is locked already, set a bit indicating we're waiting - if (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) == nullptr) - return true; - - qint64 nstimeout = timeout * Q_INT64_C(1000) * 1000; - qint64 remainingTime = nstimeout; - forever { - // successfully set the waiting bit, now sleep - if (IsTimed && nstimeout >= 0) { - bool r = futexWait(d_ptr, dummyFutexValue(), remainingTime); - if (!r) - return false; - - // we got woken up, so try to acquire the mutex - // note we must set to dummyFutexValue because there could be other threads - // also waiting - if (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) == nullptr) - return true; - - // recalculate the timeout - remainingTime = nstimeout - elapsedTimer->nsecsElapsed(); - if (remainingTime <= 0) - return false; - } else { - futexWait(d_ptr, dummyFutexValue()); - - // we got woken up, so try to acquire the mutex - // note we must set to dummyFutexValue because there could be other threads - // also waiting - if (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) == nullptr) - return true; - } - } - - Q_ASSERT(d_ptr.loadRelaxed()); - return true; -} - -void QBasicMutex::lockInternal() noexcept -{ - Q_ASSERT(!isRecursive()); - lockInternal_helper<false>(d_ptr); -} - -bool QBasicMutex::lockInternal(int timeout) noexcept -{ - Q_ASSERT(!isRecursive()); - QElapsedTimer elapsedTimer; - elapsedTimer.start(); - return lockInternal_helper<true>(d_ptr, timeout, &elapsedTimer); -} - -void QBasicMutex::unlockInternal() noexcept -{ - QMutexData *d = d_ptr.loadRelaxed(); - Q_ASSERT(d); //we must be locked - Q_ASSERT(d != dummyLocked()); // testAndSetRelease(dummyLocked(), 0) failed - Q_UNUSED(d); - Q_ASSERT(!isRecursive()); - - d_ptr.storeRelease(nullptr); - futexWakeOne(d_ptr); -} - -QT_END_NAMESPACE |