Split the timed mutex lock from the non-timed lock functions

Non-timed mutex locks are by far more common, so let's try not to
penalise the locking of those with code that won't get used that
often.

Change-Id: I37f56d6429836467fdec2e588c0fb22d914b5d75
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
This commit is contained in:
Thiago Macieira 2012-08-11 12:18:45 +02:00 committed by Qt by Nokia
parent fc174a3728
commit d8eb52fc45
3 changed files with 91 additions and 6 deletions

View File

@ -361,6 +361,14 @@ bool QBasicMutex::isRecursive()
/*!
\internal helper for lock()
*/
void QBasicMutex::lockInternal() QT_MUTEX_LOCK_NOEXCEPT
{
lockInternal(-1);
}
/*!
\internal helper for lock(int)
*/
bool QBasicMutex::lockInternal(int timeout) QT_MUTEX_LOCK_NOEXCEPT
{
Q_ASSERT(!isRecursive());

View File

@ -89,7 +89,8 @@ private:
return d_ptr.testAndSetRelease(dummyLocked(), 0);
}
bool lockInternal(int timeout = -1) QT_MUTEX_LOCK_NOEXCEPT;
void lockInternal() QT_MUTEX_LOCK_NOEXCEPT;
bool lockInternal(int timeout) QT_MUTEX_LOCK_NOEXCEPT;
void unlockInternal() Q_DECL_NOTHROW;
QBasicAtomicPointer<QMutexData> d_ptr;

View File

@ -1,6 +1,7 @@
/****************************************************************************
**
** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
** Copyright (C) 2012 Intel Corporation
** Contact: http://www.qt-project.org/
**
** This file is part of the QtCore module of the Qt Toolkit.
@ -53,12 +54,71 @@
#include <errno.h>
#include <asm/unistd.h>
#if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
// C++11 mode
# include <type_traits>
static void checkElapsedTimerIsTrivial()
{
Q_STATIC_ASSERT(std::has_trivial_default_constructor<QT_PREPEND_NAMESPACE(QElapsedTimer)>::value);
}
#else
static void checkElapsedTimerIsTrivial()
{
}
#endif
#ifndef QT_LINUX_FUTEX
# error "Qt build is broken: qmutex_linux.cpp is being built but futex support is not wanted"
#endif
QT_BEGIN_NAMESPACE
/*
* 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 QBasicAtomicInt futexFlagSupport = Q_BASIC_ATOMIC_INITIALIZER(-1);
static int checkFutexPrivateSupport()
@ -114,22 +174,25 @@ static inline QMutexData *dummyFutexValue()
return reinterpret_cast<QMutexData *>(quintptr(3));
}
bool QBasicMutex::lockInternal(int timeout) Q_DECL_NOTHROW
template <bool IsTimed> static inline
bool lockInternal_helper(QBasicAtomicPointer<QMutexData> &d_ptr, int timeout = -1) Q_DECL_NOTHROW
{
Q_ASSERT(!isRecursive());
if (!IsTimed)
timeout = -1;
// we're here because fastTryLock() has just failed
if (timeout == 0)
return false;
QElapsedTimer elapsedTimer;
if (timeout >= 1)
checkElapsedTimerIsTrivial();
if (IsTimed)
elapsedTimer.start();
// the mutex is locked already, set a bit indicating we're waiting
while (d_ptr.fetchAndStoreAcquire(dummyFutexValue()) != 0) {
struct timespec ts, *pts = 0;
if (timeout >= 1) {
if (IsTimed) {
// recalculate the timeout
qint64 xtimeout = qint64(timeout) * 1000 * 1000;
xtimeout -= elapsedTimer.nsecsElapsed();
@ -144,7 +207,7 @@ bool QBasicMutex::lockInternal(int timeout) Q_DECL_NOTHROW
// successfully set the waiting bit, now sleep
int r = _q_futex(&d_ptr, FUTEX_WAIT, quintptr(dummyFutexValue()), pts);
if (r != 0 && errno == ETIMEDOUT)
if (IsTimed && r != 0 && errno == ETIMEDOUT)
return false;
// we got woken up, so try to acquire the mutex
@ -156,6 +219,19 @@ bool QBasicMutex::lockInternal(int timeout) Q_DECL_NOTHROW
return true;
}
void QBasicMutex::lockInternal() Q_DECL_NOTHROW
{
Q_ASSERT(!isRecursive());
lockInternal_helper<false>(d_ptr);
}
bool QBasicMutex::lockInternal(int timeout) Q_DECL_NOTHROW
{
Q_ASSERT(!isRecursive());
Q_ASSERT(timeout >= 0);
return lockInternal_helper<true>(d_ptr, timeout);
}
void QBasicMutex::unlockInternal() Q_DECL_NOTHROW
{
QMutexData *d = d_ptr.load();