diff options
Diffstat (limited to 'src/corelib/thread/qmutex.cpp')
| -rw-r--r-- | src/corelib/thread/qmutex.cpp | 107 |
1 files changed, 53 insertions, 54 deletions
diff --git a/src/corelib/thread/qmutex.cpp b/src/corelib/thread/qmutex.cpp index b85a22d..1009f7b 100644 --- a/src/corelib/thread/qmutex.cpp +++ b/src/corelib/thread/qmutex.cpp @@ -45,6 +45,7 @@ #ifndef QT_NO_THREAD #include "qatomic.h" +#include "qelapsedtimer.h" #include "qthread.h" #include "qmutex_p.h" @@ -157,15 +158,12 @@ void QMutex::lock() return; } - bool isLocked = d->contenders.fetchAndAddAcquire(1) == 0; + bool isLocked = d->contenders.testAndSetAcquire(0, 1); if (!isLocked) { // didn't get the lock, wait for it isLocked = d->wait(); Q_ASSERT_X(isLocked, "QMutex::lock", "Internal error, infinite wait has timed out."); - - // don't need to wait for the lock anymore - d->contenders.deref(); } d->owner = self; @@ -174,8 +172,7 @@ void QMutex::lock() return; } - - bool isLocked = d->contenders == 0 && d->contenders.testAndSetAcquire(0, 1); + bool isLocked = d->contenders.testAndSetAcquire(0, 1); if (!isLocked) { lockInternal(); } @@ -211,7 +208,7 @@ bool QMutex::tryLock() return true; } - bool isLocked = d->contenders == 0 && d->contenders.testAndSetAcquire(0, 1); + bool isLocked = d->contenders.testAndSetAcquire(0, 1); if (!isLocked) { // some other thread has the mutex locked, or we tried to // recursively lock an non-recursive mutex @@ -224,13 +221,7 @@ bool QMutex::tryLock() return isLocked; } - bool isLocked = d->contenders == 0 && d->contenders.testAndSetAcquire(0, 1); - if (!isLocked) { - // some other thread has the mutex locked, or we tried to - // recursively lock an non-recursive mutex - return isLocked; - } - return isLocked; + return d->contenders.testAndSetAcquire(0, 1); } /*! \overload @@ -269,13 +260,10 @@ bool QMutex::tryLock(int timeout) return true; } - bool isLocked = d->contenders.fetchAndAddAcquire(1) == 0; + bool isLocked = d->contenders.testAndSetAcquire(0, 1); if (!isLocked) { // didn't get the lock, wait for it isLocked = d->wait(timeout); - - // don't need to wait for the lock anymore - d->contenders.deref(); if (!isLocked) return false; } @@ -286,17 +274,9 @@ bool QMutex::tryLock(int timeout) return true; } - bool isLocked = d->contenders.fetchAndAddAcquire(1) == 0; - if (!isLocked) { - // didn't get the lock, wait for it - isLocked = d->wait(timeout); - - // don't need to wait for the lock anymore - d->contenders.deref(); - if (!isLocked) - return false; - } - return true; + return (d->contenders.testAndSetAcquire(0, 1) + // didn't get the lock, wait for it + || d->wait(timeout)); } @@ -310,7 +290,6 @@ bool QMutex::tryLock(int timeout) void QMutex::unlock() { QMutexPrivate *d = static_cast<QMutexPrivate *>(this->d); - if (d->recursive) { if (!--d->count) { d->owner = 0; @@ -451,37 +430,57 @@ void QMutex::unlock() void QMutex::lockInternal() { QMutexPrivate *d = static_cast<QMutexPrivate *>(this->d); - int spinCount = 0; - int lastSpinCount = d->lastSpinCount; - enum { AdditionalSpins = 20, SpinCountPenalizationDivisor = 4 }; - const int maximumSpinCount = lastSpinCount + AdditionalSpins; + if (QThread::idealThreadCount() == 1) { + // don't spin on single cpu machines + bool isLocked = d->wait(); + Q_ASSERT_X(isLocked, "QMutex::lock", + "Internal error, infinite wait has timed out."); + Q_UNUSED(isLocked); + return; + } + QElapsedTimer elapsedTimer; + elapsedTimer.start(); do { - if (spinCount++ > maximumSpinCount) { - // puts("spinning useless, sleeping"); - bool isLocked = d->contenders.fetchAndAddAcquire(1) == 0; - if (!isLocked) { - - // didn't get the lock, wait for it - isLocked = d->wait(); - Q_ASSERT_X(isLocked, "QMutex::lock", - "Internal error, infinite wait has timed out."); - - // don't need to wait for the lock anymore - d->contenders.deref(); + qint64 spinTime = elapsedTimer.nsecsElapsed(); + if (spinTime > d->maximumSpinTime) { + // didn't get the lock, wait for it, since we're not going to gain anything by spinning more + elapsedTimer.start(); + bool isLocked = d->wait(); + Q_ASSERT_X(isLocked, "QMutex::lock", + "Internal error, infinite wait has timed out."); + Q_UNUSED(isLocked); + + qint64 maximumSpinTime = d->maximumSpinTime; + qint64 averageWaitTime = d->averageWaitTime; + qint64 actualWaitTime = elapsedTimer.nsecsElapsed(); + if (actualWaitTime < (QMutexPrivate::MaximumSpinTimeThreshold * 3 / 2)) { + // measure the wait times + averageWaitTime = d->averageWaitTime = qMin((averageWaitTime + actualWaitTime) / 2, qint64(QMutexPrivate::MaximumSpinTimeThreshold)); } - // decrease the lastSpinCount since we didn't actually get the lock by spinning - spinCount = -d->lastSpinCount / SpinCountPenalizationDivisor; - break; + + // adjust the spin count when spinning does not benefit contention performance + if ((spinTime + actualWaitTime) - qint64(QMutexPrivate::MaximumSpinTimeThreshold) >= qint64(QMutexPrivate::MaximumSpinTimeThreshold)) { + // long waits, stop spinning + d->maximumSpinTime = 0; + } else { + // allow spinning if wait times decrease, but never spin more than the average wait time (otherwise we may perform worse) + d->maximumSpinTime = qBound(qint64(averageWaitTime * 3 / 2), maximumSpinTime / 2, qint64(QMutexPrivate::MaximumSpinTimeThreshold)); + } + return; } + // be a good citizen... yielding lets something else run if there is something to run, but may also relieve memory pressure if not + QThread::yieldCurrentThread(); } while (d->contenders != 0 || !d->contenders.testAndSetAcquire(0, 1)); - // adjust the last spin lock count - lastSpinCount = d->lastSpinCount; - d->lastSpinCount = spinCount >= 0 - ? qMax(lastSpinCount, spinCount) - : lastSpinCount + spinCount; + // spinning is working, do not change the spin time (unless we are using much less time than allowed to spin) + qint64 maximumSpinTime = d->maximumSpinTime; + qint64 spinTime = elapsedTimer.nsecsElapsed(); + if (spinTime < maximumSpinTime / 2) { + // we are using much less time than we need, adjust the limit + d->maximumSpinTime = qBound(qint64(d->averageWaitTime * 3 / 2), maximumSpinTime / 2, qint64(QMutexPrivate::MaximumSpinTimeThreshold)); + } } /*! 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