内容

• 公共类型
• 公共函数
• 静态公共成员
• 相关非成员
• 详细描述
• 参考时钟
• 计时器类型
• std::chrono 兼容性

QDeadlineTimer 类

The QDeadlineTimer class marks a deadline in the future. 更多...

头：	#include <QDeadlineTimer>
qmake:	QT += core
Since:	Qt 5.8

• 所有成员列表，包括继承成员

注意： 此类的所有函数 可重入 .

公共类型

enum	ForeverConstant { Forever }

公共函数

	QDeadlineTimer (Qt::TimerType timerType = Qt::CoarseTimer)
	QDeadlineTimer (ForeverConstant forever , Qt::TimerType timerType = Qt::CoarseTimer)
	QDeadlineTimer (qint64 msecs , Qt::TimerType type = Qt::CoarseTimer)
	QDeadlineTimer (std::chrono::time_point<Clock, Duration> deadline , Qt::TimerType type = Qt::CoarseTimer)
	QDeadlineTimer (std::chrono::duration<Rep, Period> remaining , Qt::TimerType type = Qt::CoarseTimer)
qint64	deadline () const
std::chrono::time_point<Clock, Duration>	deadline () const
qint64	deadlineNSecs () const
bool	hasExpired () const
bool	isForever () const
qint64	remainingTime () const
std::chrono::nanoseconds	remainingTimeAsDuration () const
qint64	remainingTimeNSecs () const
void	setDeadline (qint64 msecs , Qt::TimerType timerType = Qt::CoarseTimer)
void	setDeadline (std::chrono::time_point<Clock, Duration> deadline , Qt::TimerType type = Qt::CoarseTimer)
void	setPreciseDeadline (qint64 secs , qint64 nsecs = 0, Qt::TimerType timerType = Qt::CoarseTimer)
void	setPreciseRemainingTime (qint64 secs , qint64 nsecs = 0, Qt::TimerType timerType = Qt::CoarseTimer)
void	setRemainingTime (qint64 msecs , Qt::TimerType timerType = Qt::CoarseTimer)
void	setRemainingTime (std::chrono::duration<Rep, Period> remaining , Qt::TimerType type = Qt::CoarseTimer)
void	setTimerType (Qt::TimerType timerType )
void	swap (QDeadlineTimer & other )
Qt::TimerType	timerType () const
QDeadlineTimer &	operator+= (qint64 msecs )
QDeadlineTimer &	operator-= (qint64 msecs )
QDeadlineTimer &	operator= (std::chrono::time_point<Clock, Duration> deadline_ )
QDeadlineTimer &	operator= (std::chrono::duration<Rep, Period> remaining )

静态公共成员

QDeadlineTimer	addNSecs (QDeadlineTimer dt , qint64 nsecs )
QDeadlineTimer	current (Qt::TimerType timerType = Qt::CoarseTimer)

相关非成员

bool	operator!= (QDeadlineTimer d1 , QDeadlineTimer d2 )
QDeadlineTimer	operator+ (QDeadlineTimer dt , qint64 msecs )
QDeadlineTimer	operator+ (qint64 msecs , QDeadlineTimer dt )
QDeadlineTimer	operator- (QDeadlineTimer dt , qint64 msecs )
bool	operator< (QDeadlineTimer d1 , QDeadlineTimer d2 )
bool	operator<= (QDeadlineTimer d1 , QDeadlineTimer d2 )
bool	operator== (QDeadlineTimer d1 , QDeadlineTimer d2 )
bool	operator> (QDeadlineTimer d1 , QDeadlineTimer d2 )
bool	operator>= (QDeadlineTimer d1 , QDeadlineTimer d2 )

详细描述

The QDeadlineTimer class marks a deadline in the future.

The QDeadlineTimer class is usually used to calculate future deadlines and verify whether the deadline has expired. QDeadlineTimer can also be used for deadlines without expiration ("forever"). It forms a counterpart to QElapsedTimer ，计算已消耗多少时间从 QElapsedTimer::start () 被调用。

QDeadlineTimer provides a more convenient API compared to QElapsedTimer::hasExpired ().

The typical use-case for the class is to create a QDeadlineTimer before the operation in question is started, and then use remainingTime () 或 hasExpired () to determine whether to continue trying the operation. QDeadlineTimer objects can be passed to functions being called to execute this operation so they know how long to still operate.

void executeOperation(int msecs)
{
    QDeadlineTimer deadline(msecs);
    do {
        if (readFromDevice(deadline.remainingTime())
            break;
        waitForReadyRead(deadline);
    } while (!deadline.hasExpired());
}
					

Many QDeadlineTimer functions deal with time out values, which all are measured in milliseconds. There are two special values, the same as many other Qt functions named waitFor 或类似：

• 0：没有剩余时间，过期
• -1：无限剩余时间，计时器从不过期

参考时钟

QDeadlineTimer will use the same clock as QElapsedTimer (见 QElapsedTimer::clockType () 和 QElapsedTimer::isMonotonic ()).

计时器类型

像 QTimer , QDeadlineTimer can select among different levels of coarseness on the timers. You can select precise timing by passing Qt::PreciseTimer to the functions that set of change the timer, or you can select coarse timing by passing Qt::CoarseTimer . Qt::VeryCoarseTimer is currently interpreted the same way as Qt::CoarseTimer .

This feature is dependent on support from the operating system: if the OS does not support a coarse timer functionality, then QDeadlineTimer will behave like Qt::PreciseTimer was passed.

QDeadlineTimer 默认为 Qt::CoarseTimer because on operating systems that do support coarse timing, making timing calls to that clock source is often much more efficient. The level of coarseness depends on the operating system, but should be in the order of a couple of milliseconds.

std::chrono 兼容性

QDeadlineTimer is compatible with the std::chrono API from C++11 and can be constructed from or compared to both std::chrono::duration and std::chrono::time_point objects. In addition, it is fully compatible with the time literals from C++14, which allow one to write code as:

using namespace std::chrono;
using namespace std::chrono_literals;
QDeadlineTimer deadline(30s);
device->waitForReadyRead(deadline);
if (deadline.remainingTime<nanoseconds>() > 300ms)
    cleanup();
					

As can be seen in the example above, QDeadlineTimer offers a templated version of remainingTime () 和 deadline () that can be used to return std::chrono 对象。

Note that comparing to time_point is not as efficient as comparing to duration , since QDeadlineTimer may need to convert from its own internal clock source to the clock source used by the time_point object. Also note that, due to this conversion, the deadlines will not be precise, so the following code is not expected to compare equally:

using namespace std::chrono;
using namespace std::chrono_literals;
auto now = steady_clock::now();
QDeadlineTimer deadline(now + 1s);
Q_ASSERT(deadline == now + 1s);
					

另请参阅 QTime , QTimer , QDeadlineTimer ，和 Qt::TimerType .

成员类型文档编制

enum QDeadlineTimer:: ForeverConstant

常量	值	描述
QDeadlineTimer::Forever	0	使用当创建 QDeadlineTimer 以指示截止日期不应该过期

成员函数文档编制

QDeadlineTimer:: QDeadlineTimer ( Qt::TimerType timerType = Qt::CoarseTimer)

Constructs an expired QDeadlineTimer object. For this object, remainingTime () will return 0.

The timer type timerType may be ignored, since the timer is already expired. Similarly, for optimization purposes, this function will not attempt to obtain the current time and will use a value known to be in the past. Therefore, deadline () may return an unexpected value and this object cannot be used in calculation of how long it is overdue. If that functionality is required, use QDeadlineTimer::current ().

另请参阅 hasExpired (), remainingTime (), Qt::TimerType ，和 current ().

QDeadlineTimer:: QDeadlineTimer ( ForeverConstant forever , Qt::TimerType timerType = Qt::CoarseTimer)

QDeadlineTimer objects created with parameter forever never expire. For such objects, remainingTime () will return -1, deadline () will return the maximum value, and isForever () will return true.

The timer type timerType may be ignored, since the timer is already expired.

另请参阅 ForeverConstant , hasExpired (), isForever (), remainingTime ()，和 timerType ().

QDeadlineTimer:: QDeadlineTimer ( qint64 msecs , Qt::TimerType type = Qt::CoarseTimer)

构造 QDeadlineTimer object with an expiry time of msecs msecs from the moment of the creation of this object, if msecs is positive. If msecs is zero, this QDeadlineTimer will be marked as expired, causing remainingTime () to return zero and deadline () to return an indeterminate time point in the past. If msecs is -1, the timer will be set it to never expire, causing remainingTime () to return -1 and deadline () to return the maximum value.

The QDeadlineTimer object will be constructed with the specified timer type .

For optimization purposes, if msecs is zero, this function may skip obtaining the current time and may instead use a value known to be in the past. If that happens, deadline () may return an unexpected value and this object cannot be used in calculation of how long it is overdue. If that functionality is required, use QDeadlineTimer::current () and add time to it.

另请参阅 hasExpired (), isForever (), remainingTime ()，和 setRemainingTime ().

QDeadlineTimer:: QDeadlineTimer ( std::chrono::time_point < Clock , Duration > deadline , Qt::TimerType type = Qt::CoarseTimer)

构造 QDeadlineTimer object with a deadline at deadline time point, converting from the clock source Clock to Qt's internal clock source (see QElapsedTimer::clcokType()).

若 deadline is in the past, this QDeadlineTimer object is set to expired, whereas if deadline 等于 Duration::max() , then this object is set to never expire.

The QDeadlineTimer object will be constructed with the specified timer type .

另请参阅 hasExpired (), isForever (), remainingTime ()，和 setDeadline ().

QDeadlineTimer:: QDeadlineTimer ( std::chrono::duration < Rep , Period > remaining , Qt::TimerType type = Qt::CoarseTimer)

构造 QDeadlineTimer object with a remaining time of remaining 。若 remaining is zero or negative, this QDeadlineTimer object will be mark as expired, whereas if remaining 等于 duration::max() , the object will be set to never expire.

The QDeadlineTimer object will be constructed with the specified timer type .

此构造函数可以用于 C++ 14 的用户定义时间文字，譬如在：

using namespace std::chrono_literals;
QDeadlineTimer deadline(250ms);
					

For optimization purposes, if remaining is zero or negative, this function may skip obtaining the current time and may instead use a value known to be in the past. If that happens, deadline () may return an unexpected value and this object cannot be used in calculation of how long it is overdue. If that functionality is required, use QDeadlineTimer::current () and add time to it.

另请参阅 hasExpired (), isForever (), remainingTime ()，和 setRemainingTime ().

[static] QDeadlineTimer QDeadlineTimer:: addNSecs ( QDeadlineTimer dt , qint64 nsecs )

返回 QDeadlineTimer object whose deadline is extended from dt 's deadline by nsecs nanoseconds. If dt was set to never expire, this function returns a QDeadlineTimer that will not expire either.

注意： if dt was created as expired, its deadline is indeterminate and adding an amount of time may or may not cause it to become unexpired.

[static] QDeadlineTimer QDeadlineTimer:: current ( Qt::TimerType timerType = Qt::CoarseTimer)

返回 QDeadlineTimer that is expired but is guaranteed to contain the current time. Objects created by this function can participate in the calculation of how long a timer is overdue, using the deadline () 函数。

The QDeadlineTimer object will be constructed with the specified timerType .

qint64 QDeadlineTimer:: deadline () const

Returns the absolute time point for the deadline stored in QDeadlineTimer object, calculated in milliseconds relative to the reference clock, the same as QElapsedTimer::msecsSinceReference (). The value will be in the past if this QDeadlineTimer has expired.

若此 QDeadlineTimer never expires, this function returns std::numeric_limits<qint64>::max() .

This function can be used to calculate the amount of time a timer is overdue, by subtracting QDeadlineTimer::current () 或 QElapsedTimer::msecsSinceReference (), as in the following example:

qint64 realTimeLeft = deadline.deadline();
if (realTimeLeft != (std::numeric_limits<qint64>::max)()) {
    realTimeLeft -= QDeadlineTimer::current().deadline();
    // or:
    //QElapsedTimer timer;
    //timer.start();
    //realTimeLeft -= timer.msecsSinceReference();
}
					

注意： Timers that were created as expired have an indetermine time point in the past as their deadline, so the above calculation may not work.

另请参阅 remainingTime (), deadlineNSecs ()，和 setDeadline ().

std::chrono::time_point < Clock , Duration > QDeadlineTimer:: deadline () const

qint64 QDeadlineTimer:: deadlineNSecs () const

Returns the absolute time point for the deadline stored in QDeadlineTimer object, calculated in nanoseconds relative to the reference clock, the same as QElapsedTimer::msecsSinceReference (). The value will be in the past if this QDeadlineTimer has expired.

若此 QDeadlineTimer never expires, this function returns std::numeric_limits<qint64>::max() .

This function can be used to calculate the amount of time a timer is overdue, by subtracting QDeadlineTimer::current (), as in the following example:

qint64 realTimeLeft = deadline.deadlineNSecs();
if (realTimeLeft != std::numeric_limits<qint64>::max())
    realTimeLeft -= QDeadlineTimer::current().deadlineNSecs();
					

注意： Timers that were created as expired have an indetermine time point in the past as their deadline, so the above calculation may not work.

另请参阅 remainingTime () and deadlineNSecs().

bool QDeadlineTimer:: hasExpired () const

返回 true，若此 QDeadlineTimer object has expired, false if there remains time left. For objects that have expired, remainingTime () will return zero and deadline () will return a time point in the past.

QDeadlineTimer objects created with the ForeverConstant never expire and this function always returns false for them.

另请参阅 isForever () 和 remainingTime ().

bool QDeadlineTimer:: isForever () const

返回 true，若此 QDeadlineTimer object never expires, false otherwise. For timers that never expire, remainingTime () always returns -1 and deadline () returns the maximum value.

另请参阅 ForeverConstant , hasExpired ()，和 remainingTime ().

qint64 QDeadlineTimer:: remainingTime () const

返回剩余时间在此 QDeadlineTimer object in milliseconds. If the timer has already expired, this function will return zero and it is not possible to obtain the amount of time overdue with this function (to do that, see deadline ()). If the timer was set to never expire, this function returns -1.

This function is suitable for use in Qt APIs that take a millisecond timeout, such as the many QIODevice waitFor functions or the timed lock functions in QMutex , QWaitCondition , QSemaphore ，或 QReadWriteLock 。例如：

mutex.tryLock(deadline.remainingTime());
					

另请参阅 setRemainingTime (), remainingTimeNSecs (), isForever ()，和 hasExpired ().

std::chrono::nanoseconds QDeadlineTimer:: remainingTimeAsDuration () const

返回截止日期之前的剩余时间。

qint64 QDeadlineTimer:: remainingTimeNSecs () const

返回剩余时间在此 QDeadlineTimer object in nanoseconds. If the timer has already expired, this function will return zero and it is not possible to obtain the amount of time overdue with this function. If the timer was set to never expire, this function returns -1.

另请参阅 remainingTime (), isForever ()，和 hasExpired ().

void QDeadlineTimer:: setDeadline ( qint64 msecs , Qt::TimerType timerType = Qt::CoarseTimer)

设置截止日期为此 QDeadlineTimer object to be the msecs absolute time point, counted in milliseconds since the reference clock (the same as QElapsedTimer::msecsSinceReference ()), and the timer type to timerType . If the value is in the past, this QDeadlineTimer will be marked as expired.

若 msecs is std::numeric_limits<qint64>::max() , this QDeadlineTimer will be set to never expire.

另请参阅 setPreciseDeadline (), deadline (), deadlineNSecs ()，和 setRemainingTime ().

void QDeadlineTimer:: setDeadline ( std::chrono::time_point < Clock , Duration > deadline , Qt::TimerType type = Qt::CoarseTimer)

设置此 QDeadlineTimer to the deadline marked by deadline time point, converting from the clock source Clock to Qt's internal clock source (see QElapsedTimer::clcokType()).

若 deadline is in the past, this QDeadlineTimer object is set to expired, whereas if deadline 等于 Duration::max() , then this object is set to never expire.

The timer type for this QDeadlineTimer object will be set to the specified type .

另请参阅 hasExpired (), isForever ()，和 remainingTime ().

void QDeadlineTimer:: setPreciseDeadline ( qint64 secs , qint64 nsecs = 0, Qt::TimerType timerType = Qt::CoarseTimer)

设置截止日期为此 QDeadlineTimer object to be secs seconds and nsecs nanoseconds since the reference clock epoch (the same as QElapsedTimer::msecsSinceReference ()), and the timer type to timerType . If the value is in the past, this QDeadlineTimer will be marked as expired.

若 secs or nsecs is std::numeric_limits<qint64>::max() , this QDeadlineTimer will be set to never expire. If nsecs is more than 1 billion nanoseconds (1 second), then secs will be adjusted accordingly.

另请参阅 setDeadline (), deadline (), deadlineNSecs ()，和 setRemainingTime ().

void QDeadlineTimer:: setPreciseRemainingTime ( qint64 secs , qint64 nsecs = 0, Qt::TimerType timerType = Qt::CoarseTimer)

设置剩余时间为此 QDeadlineTimer 对象到 secs seconds plus nsecs nanoseconds from now, if secs has a positive value. If secs is -1, this QDeadlineTimer will be set it to never expire. If both parameters are zero, this QDeadlineTimer will be marked as expired.

The timer type for this QDeadlineTimer object will be set to the specified timerType .

另请参阅 setRemainingTime (), hasExpired (), isForever ()，和 remainingTime ().

void QDeadlineTimer:: setRemainingTime ( qint64 msecs , Qt::TimerType timerType = Qt::CoarseTimer)

设置剩余时间为此 QDeadlineTimer 对象到 msecs milliseconds from now, if msecs has a positive value. If msecs is zero, this QDeadlineTimer object will be marked as expired, whereas a value of -1 will set it to never expire.

The timer type for this QDeadlineTimer object will be set to the specified timerType .

另请参阅 setPreciseRemainingTime (), hasExpired (), isForever ()，和 remainingTime ().

void QDeadlineTimer:: setRemainingTime ( std::chrono::duration < Rep , Period > remaining , Qt::TimerType type = Qt::CoarseTimer)

这是重载函数。

设置剩余时间为此 QDeadlineTimer 对象到 remaining 。若 remaining is zero or negative, this QDeadlineTimer object will be mark as expired, whereas if remaining 等于 duration::max() , the object will be set to never expire.

The timer type for this QDeadlineTimer object will be set to the specified type .

This function can be used with C++14's user-defined literals for time, such as in:

using namespace std::chrono_literals;
deadline.setRemainingTime(250ms);
					

另请参阅 setDeadline (), remainingTime (), hasExpired ()，和 isForever ().

void QDeadlineTimer:: setTimerType ( Qt::TimerType timerType )

Changes the timer type for this object to timerType .

The behavior for each possible value of timerType is operating-system dependent. Qt::PreciseTimer will use the most precise timer that Qt can find, with resolution of 1 millisecond or better, whereas QDeadlineTimer will try to use a more coarse timer for Qt::CoarseTimer and Qt::VeryCoarseTimer .

另请参阅 timerType () 和 Qt::TimerType .

void QDeadlineTimer:: swap ( QDeadlineTimer & other )

Swaps this deadline timer with the other deadline timer.

Qt::TimerType QDeadlineTimer:: timerType () const

Returns the timer type is active for this object.

另请参阅 setTimerType ().

QDeadlineTimer &QDeadlineTimer:: operator+= ( qint64 msecs )

Extends this QDeadlineTimer object by msecs milliseconds and returns itself. If this object is set to never expire, this function does nothing.

To add times of precision greater than 1 millisecond, use addNSecs ().

QDeadlineTimer &QDeadlineTimer:: operator-= ( qint64 msecs )

Shortens this QDeadlineTimer object by msecs milliseconds and returns itself. If this object is set to never expire, this function does nothing.

To subtract times of precision greater than 1 millisecond, use addNSecs ().

QDeadlineTimer &QDeadlineTimer:: operator= ( std::chrono::time_point < Clock , Duration > deadline_ )

赋值 deadline_ 到此截止日期计时器。

QDeadlineTimer &QDeadlineTimer:: operator= ( std::chrono::duration < Rep , Period > remaining )

Sets this deadline timer to the remaining time.

相关非成员

bool operator!= ( QDeadlineTimer d1 , QDeadlineTimer d2 )

Returns true if the deadline on d1 and the deadline in d2 are diferent, false otherwise. The timer type used to create the two deadlines is ignored. This function is equivalent to:

return d1.deadlineNSecs() != d2.deadlineNSecs();
					

注意： 比较 QDeadlineTimer objects with different timer types is not supported and may result in unpredictable behavior.

QDeadlineTimer operator+ ( QDeadlineTimer dt , qint64 msecs )

返回 QDeadlineTimer object whose deadline is msecs later than the deadline stored in dt 。若 dt is set to never expire, this function returns a QDeadlineTimer that does not expire either.

To add times of precision greater than 1 millisecond, use addNSecs().

QDeadlineTimer operator+ ( qint64 msecs , QDeadlineTimer dt )

返回 QDeadlineTimer object whose deadline is msecs later than the deadline stored in dt 。若 dt is set to never expire, this function returns a QDeadlineTimer that does not expire either.

To add times of precision greater than 1 millisecond, use addNSecs().

QDeadlineTimer operator- ( QDeadlineTimer dt , qint64 msecs )

返回 QDeadlineTimer object whose deadline is msecs before the deadline stored in dt 。若 dt is set to never expire, this function returns a QDeadlineTimer that does not expire either.

To subtract times of precision greater than 1 millisecond, use addNSecs().

bool operator< ( QDeadlineTimer d1 , QDeadlineTimer d2 )

Returns true if the deadline on d1 is earlier than the deadline in d2 , false otherwise. The timer type used to create the two deadlines is ignored. This function is equivalent to:

return d1.deadlineNSecs() < d2.deadlineNSecs();
					

注意： 比较 QDeadlineTimer objects with different timer types is not supported and may result in unpredictable behavior.

bool operator<= ( QDeadlineTimer d1 , QDeadlineTimer d2 )

Returns true if the deadline on d1 is earlier than or the same as the deadline in d2 , false otherwise. The timer type used to create the two deadlines is ignored. This function is equivalent to:

return d1.deadlineNSecs() <= d2.deadlineNSecs();
					

注意： 比较 QDeadlineTimer objects with different timer types is not supported and may result in unpredictable behavior.

bool operator== ( QDeadlineTimer d1 , QDeadlineTimer d2 )

Returns true if the deadline on d1 and the deadline in d2 are the same, false otherwise. The timer type used to create the two deadlines is ignored. This function is equivalent to:

return d1.deadlineNSecs() == d2.deadlineNSecs();
					

注意： 比较 QDeadlineTimer objects with different timer types is not supported and may result in unpredictable behavior.

bool operator> ( QDeadlineTimer d1 , QDeadlineTimer d2 )

Returns true if the deadline on d1 is later than the deadline in d2 , false otherwise. The timer type used to create the two deadlines is ignored. This function is equivalent to:

return d1.deadlineNSecs() > d2.deadlineNSecs();
					

注意： 比较 QDeadlineTimer objects with different timer types is not supported and may result in unpredictable behavior.

bool operator>= ( QDeadlineTimer d1 , QDeadlineTimer d2 )

Returns true if the deadline on d1 is later than or the same as the deadline in d2 , false otherwise. The timer type used to create the two deadlines is ignored. This function is equivalent to:

return d1.deadlineNSecs() >= d2.deadlineNSecs();
					

注意： 比较 QDeadlineTimer objects with different timer types is not supported and may result in unpredictable behavior.