diff options
Diffstat (limited to 'src/corelib/kernel/qelapsedtimer.cpp')
| -rw-r--r-- | src/corelib/kernel/qelapsedtimer.cpp | 329 |
1 files changed, 244 insertions, 85 deletions
diff --git a/src/corelib/kernel/qelapsedtimer.cpp b/src/corelib/kernel/qelapsedtimer.cpp index af26a523c0..511b81a04e 100644 --- a/src/corelib/kernel/qelapsedtimer.cpp +++ b/src/corelib/kernel/qelapsedtimer.cpp @@ -1,41 +1,5 @@ -/**************************************************************************** -** -** Copyright (C) 2016 The Qt Company Ltd. -** 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) 2016 The Qt Company Ltd. +// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only #include "qelapsedtimer.h" @@ -111,19 +75,7 @@ QT_BEGIN_NAMESPACE that the clock used is the same as QElapsedTimer (see QElapsedTimer::clockType()). - \section2 32-bit overflows - - Some of the clocks used by QElapsedTimer have a limited range and may - overflow after hitting the upper limit (usually 32-bit). QElapsedTimer - deals with this overflow issue and presents a consistent timing. However, - when extracting the time since reference from QElapsedTimer, two - different processes in the same machine may have different understanding - of how much time has actually elapsed. - - The information on which clocks types may overflow and how to remedy that - issue is documented along with the clock types. - - \sa QTime, QTimer, QDeadlineTimer + \sa QTime, QChronoTimer, QDeadlineTimer */ /*! @@ -138,10 +90,13 @@ QT_BEGIN_NAMESPACE used. \value SystemTime The human-readable system time. This clock is not monotonic. - \value MonotonicClock The system's monotonic clock, usually found in Unix systems. This clock is monotonic and does not overflow. - \value TickCounter The system's tick counter, used on Windows systems. This clock may overflow. - \value MachAbsoluteTime The Mach kernel's absolute time (\macos and iOS). This clock is monotonic and does not overflow. - \value PerformanceCounter The high-resolution performance counter provided by Windows. This clock is monotonic and does not overflow. + \value MonotonicClock The system's monotonic clock, usually found in Unix systems. + This clock is monotonic. + \value TickCounter Not used anymore. + \value MachAbsoluteTime The Mach kernel's absolute time (\macos and iOS). + This clock is monotonic. + \value PerformanceCounter The performance counter provided by Windows. + This clock is monotonic. \section2 SystemTime @@ -159,26 +114,6 @@ QT_BEGIN_NAMESPACE arbitrary point in the past. This clock type is used on Unix systems which support POSIX monotonic clocks (\tt{_POSIX_MONOTONIC_CLOCK}). - This clock does not overflow. - - \section2 TickCounter - - The tick counter clock type is based on the system's or the processor's - tick counter, multiplied by the duration of a tick. This clock type is - used on Windows platforms. If the high-precision performance - counter is available on Windows, the \tt{PerformanceCounter} clock type - is used instead. - - The TickCounter clock type is the only clock type that may overflow. - Windows Vista and Windows Server 2008 support the extended 64-bit tick - counter, which allows avoiding the overflow. - - On Windows systems, the clock overflows after 2^32 milliseconds, which - corresponds to roughly 49.7 days. This means two processes' reckoning of - the time since the reference may be different by multiples of 2^32 - milliseconds. When comparing such values, it's recommended that the high - 32 bits of the millisecond count be masked off. - \section2 MachAbsoluteTime This clock type is based on the absolute time presented by Mach kernels, @@ -187,17 +122,14 @@ QT_BEGIN_NAMESPACE a POSIX monotonic clock with values differing from the Mach absolute time. - This clock is monotonic and does not overflow. + This clock is monotonic. \section2 PerformanceCounter This clock uses the Windows functions \tt{QueryPerformanceCounter} and - \tt{QueryPerformanceFrequency} to access the system's high-precision - performance counter. Since this counter may not be available on all - systems, QElapsedTimer will fall back to the \tt{TickCounter} clock - automatically, if this clock cannot be used. + \tt{QueryPerformanceFrequency} to access the system's performance counter. - This clock is monotonic and does not overflow. + This clock is monotonic. \sa clockType(), isMonotonic() */ @@ -233,9 +165,229 @@ QT_BEGIN_NAMESPACE function will return false. */ +/*! + \fn QElapsedTimer::clockType() noexcept + + Returns the clock type that this QElapsedTimer implementation uses. + + Since Qt 6.6, QElapsedTimer uses \c{std::chrono::steady_clock}, so the + clock type is always \l MonotonicClock. + + \sa isMonotonic() +*/ + +QElapsedTimer::ClockType QElapsedTimer::clockType() noexcept +{ + // we use std::chrono::steady_clock + return MonotonicClock; +} + +/*! + \fn QElapsedTimer::isMonotonic() noexcept + + Returns \c true if this is a monotonic clock, false otherwise. See the + information on the different clock types to understand which ones are + monotonic. + + Since Qt 6.6, QElapsedTimer uses \c{std::chrono::steady_clock}, so this + function now always returns true. + + \sa clockType(), QElapsedTimer::ClockType +*/ +bool QElapsedTimer::isMonotonic() noexcept +{ + // We trust std::chrono::steady_clock to be steady (monotonic); if the + // Standard Library is lying to us, users must complain to their vendor. + return true; +} + +/*! + \typealias QElapsedTimer::Duration + Synonym for \c std::chrono::nanoseconds. +*/ + +/*! + \typealias QElapsedTimer::TimePoint + Synonym for \c {std::chrono::time_point<std::chrono::steady_clock, Duration>}. +*/ + +/*! + Starts this timer. Once started, a timer value can be checked with elapsed() or msecsSinceReference(). + + Normally, a timer is started just before a lengthy operation, such as: + \snippet qelapsedtimer/main.cpp 0 + + Also, starting a timer makes it valid again. + + \sa restart(), invalidate(), elapsed() +*/ +void QElapsedTimer::start() noexcept +{ + static_assert(sizeof(t1) == sizeof(Duration::rep)); + + // This assignment will work so long as TimePoint uses the same time + // duration or one of finer granularity than steady_clock::time_point. That + // means it will work until the first steady_clock using picoseconds. + TimePoint now = std::chrono::steady_clock::now(); + t1 = now.time_since_epoch().count(); + QT6_ONLY(t2 = 0); +} + +/*! + Restarts the timer and returns the number of milliseconds elapsed since + the previous start. + This function is equivalent to obtaining the elapsed time with elapsed() + and then starting the timer again with start(), but it does so in one + single operation, avoiding the need to obtain the clock value twice. + + Calling this function on a QElapsedTimer that is invalid + results in undefined behavior. + + The following example illustrates how to use this function to calibrate a + parameter to a slow operation (for example, an iteration count) so that + this operation takes at least 250 milliseconds: + + \snippet qelapsedtimer/main.cpp 3 + + \sa start(), invalidate(), elapsed(), isValid() +*/ +qint64 QElapsedTimer::restart() noexcept +{ + QElapsedTimer old = *this; + start(); + return old.msecsTo(*this); +} + +/*! + \since 6.6 + + Returns a \c{std::chrono::nanoseconds} with the time since this QElapsedTimer was last + started. + + Calling this function on a QElapsedTimer that is invalid + results in undefined behavior. + + On platforms that do not provide nanosecond resolution, the value returned + will be the best estimate available. + + \sa start(), restart(), hasExpired(), invalidate() +*/ +auto QElapsedTimer::durationElapsed() const noexcept -> Duration +{ + TimePoint then{Duration(t1)}; + return std::chrono::steady_clock::now() - then; +} + +/*! + \since 4.8 + + Returns the number of nanoseconds since this QElapsedTimer was last + started. + + Calling this function on a QElapsedTimer that is invalid + results in undefined behavior. + + On platforms that do not provide nanosecond resolution, the value returned + will be the best estimate available. + + \sa start(), restart(), hasExpired(), invalidate() +*/ +qint64 QElapsedTimer::nsecsElapsed() const noexcept +{ + return durationElapsed().count(); +} + +/*! + Returns the number of milliseconds since this QElapsedTimer was last + started. + + Calling this function on a QElapsedTimer that is invalid + results in undefined behavior. + + \sa start(), restart(), hasExpired(), isValid(), invalidate() +*/ +qint64 QElapsedTimer::elapsed() const noexcept +{ + using namespace std::chrono; + return duration_cast<milliseconds>(durationElapsed()).count(); +} + +/*! + Returns the number of milliseconds between last time this QElapsedTimer + object was started and its reference clock's start. + + This number is usually arbitrary for all clocks except the + QElapsedTimer::SystemTime clock. For that clock type, this number is the + number of milliseconds since January 1st, 1970 at 0:00 UTC (that is, it + is the Unix time expressed in milliseconds). + + On Linux, Windows and Apple platforms, this value is usually the time + since the system boot, though it usually does not include the time the + system has spent in sleep states. + + \sa clockType(), elapsed() +*/ +qint64 QElapsedTimer::msecsSinceReference() const noexcept +{ + using namespace std::chrono; + return duration_cast<milliseconds>(Duration(t1)).count(); +} + +/*! + \since 6.6 + + Returns the time difference between this QElapsedTimer and \a other as a + \c{std::chrono::nanoseconds}. If \a other was started before this object, + the returned value will be negative. If it was started later, the returned + value will be positive. + + The return value is undefined if this object or \a other were invalidated. + + \sa secsTo(), elapsed() +*/ +auto QElapsedTimer::durationTo(const QElapsedTimer &other) const noexcept -> Duration +{ + Duration d1(t1); + Duration d2(other.t1); + return d2 - d1; +} + +/*! + Returns the number of milliseconds between this QElapsedTimer and \a + other. If \a other was started before this object, the returned value + will be negative. If it was started later, the returned value will be + positive. + + The return value is undefined if this object or \a other were invalidated. + + \sa secsTo(), elapsed() +*/ +qint64 QElapsedTimer::msecsTo(const QElapsedTimer &other) const noexcept +{ + using namespace std::chrono; + return duration_cast<milliseconds>(durationTo(other)).count(); +} + +/*! + Returns the number of seconds between this QElapsedTimer and \a other. If + \a other was started before this object, the returned value will be + negative. If it was started later, the returned value will be positive. + + Calling this function on or with a QElapsedTimer that is invalid + results in undefined behavior. + + \sa msecsTo(), elapsed() +*/ +qint64 QElapsedTimer::secsTo(const QElapsedTimer &other) const noexcept +{ + using namespace std::chrono; + return duration_cast<seconds>(durationTo(other)).count(); +} + static const qint64 invalidData = Q_INT64_C(0x8000000000000000); /*! + \fn QElapsedTimer::invalidate() noexcept Marks this QElapsedTimer object as invalid. An invalid object can be checked with isValid(). Calculations of timer @@ -261,10 +413,12 @@ bool QElapsedTimer::isValid() const noexcept } /*! - Returns \c true if this QElapsedTimer has already expired by \a timeout - milliseconds (that is, more than \a timeout milliseconds have elapsed). - The value of \a timeout can be -1 to indicate that this timer does not - expire, in which case this function will always return false. + Returns \c true if elapsed() exceeds the given \a timeout, otherwise \c false. + + A negative \a timeout is interpreted as infinite, so \c false is returned in + this case. Otherwise, this is equivalent to \c {elapsed() > timeout}. You + can do the same for a duration by comparing durationElapsed() to a duration + timeout. \sa elapsed(), QDeadlineTimer */ @@ -275,4 +429,9 @@ bool QElapsedTimer::hasExpired(qint64 timeout) const noexcept return quint64(elapsed()) > quint64(timeout); } +bool operator<(const QElapsedTimer &lhs, const QElapsedTimer &rhs) noexcept +{ + return lhs.t1 < rhs.t1; +} + QT_END_NAMESPACE |