Elapsed Time Mac OS

The QElapsedTimer class provides a fast way to calculate elapsed times. More.

Aug 28, 2020 I am new Linux and Unix systems user. How do I display the time of the execution of a command/script on Linux or Unix-like operating systems using shell prompt? You need to use the time command to display the elapsed time during the execution of a command or script.donotprint. One of the more common calculations done with time values involves calculating elapsed time — that is, the number of hours and minutes between a start time and an end time. The table in the figure shows a list of start and end times along with calculated elapsed times. You can see that the formula. I'm currently working on a project at work where I need to be able to measure relative elapsed time across cores & threads in the nanosecond resolution range. An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources.

Note: All functions in this class are reentrant.

Public Types

Public Functions

Static Public Members

Detailed Description

The QElapsedTimer class provides a fast way to calculate elapsed times.

The QElapsedTimer class is usually used to quickly calculate how much time has elapsed between two events. Its API is similar to that of QTime, so code that was using that can be ported quickly to the new class.

However, unlike QTime, QElapsedTimer tries to use monotonic clocks if possible. This means it's not possible to convert QElapsedTimer objects to a human-readable time.

The typical use-case for the class is to determine how much time was spent in a slow operation. The simplest example of such a case is for debugging purposes, as in the following example:

In this example, the timer is started by a call to start() and the elapsed timer is calculated by the elapsed() function.

The time elapsed can also be used to recalculate the time available for another operation, after the first one is complete. This is useful when the execution must complete within a certain time period, but several steps are needed. The waitFor-type functions in QIODevice and its subclasses are good examples of such need. In that case, the code could be as follows:

Another use-case is to execute a certain operation for a specific timeslice. For this, QElapsedTimer provides the hasExpired() convenience function, which can be used to determine if a certain number of milliseconds has already elapsed:

Reference clocks

QElapsedTimer will use the platform's monotonic reference clock in all platforms that support it (see QElapsedTimer::isMonotonic()). This has the added benefit that QElapsedTimer is immune to time adjustments, such as the user correcting the time. Also unlike QTime, QElapsedTimer is immune to changes in the timezone settings, such as daylight savings periods.

On the other hand, this means QElapsedTimer values can only be compared with other values that use the same reference. This is especially true if the time since the reference is extracted from the QElapsedTimer object (QElapsedTimer::msecsSinceReference()) and serialised. These values should never be exchanged across the network or saved to disk, since there's no telling whether the computer node receiving the data is the same as the one originating it or if it has rebooted since.

It is, however, possible to exchange the value with other processes running on the same machine, provided that they also use the same reference clock. QElapsedTimer will always use the same clock, so it's safe to compare with the value coming from another process in the same machine. If comparing to values produced by other APIs, you should check that the clock used is the same as QElapsedTimer (see QElapsedTimer::clockType()).

32-bit overflows

Some of the clocks that 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.

See also QTime and QTimer.

Member Type Documentation

enum QElapsedTimer::ClockType

This enum contains the different clock types that QElapsedTimer may use.

QElapsedTimer will always use the same clock type in a particular machine, so this value will not change during the lifetime of a program. It is provided so that QElapsedTimer can be used with other non-Qt implementations, to guarantee that the same reference clock is being used.

SystemTime

The system time clock is purely the real time, expressed in milliseconds since Jan 1, 1970 at 0:00 UTC. It's equivalent to the value returned by the C and POSIX time function, with the milliseconds added. This clock type is currently only used on Unix systems that do not support monotonic clocks (see below).

This is the only non-monotonic clock that QElapsedTimer may use.

MonotonicClock

This is the system's monotonic clock, expressed in milliseconds since an arbitrary point in the past. This clock type is used on Unix systems which support POSIX monotonic clocks (_POSIX_MONOTONIC_CLOCK).

This clock does not overflow.

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 and Symbian platforms. If the high-precision performance counter is available on Windows, the 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's 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.

On Symbian systems, the overflow happens after 2^32 ticks, the duration of which can be obtained from the platform HAL using the constant HAL::ENanoTickPeriod. When comparing values between processes, it's necessary to divide the value by the tick duration and mask off the high 32 bits.

MachAbsoluteTime

This clock type is based on the absolute time presented by Mach kernels, such as that found on Mac OS X. This clock type is presented separately from MonotonicClock since Mac OS X is also a Unix system and may support a POSIX monotonic clock with values differing from the Mach absolute time.

This clock is monotonic and does not overflow.

PerformanceCounter

This clock uses the Windows functions QueryPerformanceCounter and 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 TickCounter clock automatically, if this clock cannot be used.

This clock is monotonic and does not overflow.

See also clockType() and isMonotonic().

Member Function Documentation

[static] ClockType QElapsedTimer::clockType()

Returns the clock type that this QElapsedTimer implementation uses.

See also isMonotonic().

qint64 QElapsedTimer::elapsed() const

Returns the number of milliseconds since this QElapsedTimer was last started. Calling this function in a QElapsedTimer that was invalidated will result in undefined results.

See also start(), restart(), hasExpired(), and invalidate().

bool QElapsedTimer::hasExpired(qint64 timeout) const

Returns true if this QElapsedTimer has already expired by timeout milliseconds (that is, more than timeout milliseconds have elapsed). The value of timeout can be -1 to indicate that this timer does not expire, in which case this function will always return false.

See also elapsed().

void QElapsedTimer::invalidate()

Marks this QElapsedTimer object as invalid.

An invalid object can be checked with isValid(). Calculations of timer elapsed since invalid data are undefined and will likely produce bizarre results.

See also isValid(), start(), and restart().

[static] bool QElapsedTimer::isMonotonic()

Returns true if this is a monotonic clock, false otherwise. Hoard hearder mac os. See the information on the different clock types to understand which ones are monotonic.

See also clockType() and QElapsedTimer::ClockType.

bool QElapsedTimer::isValid() const

Returns false if this object was invalidated by a call to invalidate() and has not been restarted since.

See also invalidate(), start(), and restart().

qint64 QElapsedTimer::msecsSinceReference() const

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).

See also clockType() and elapsed().

qint64 QElapsedTimer::msecsTo(const QElapsedTimer & other) const

Returns the number of milliseconds between this QElapsedTimer and other. If other was started before this object, the returned value will be positive. If it was started later, the returned value will be negative.

The return value is undefined if this object or other were invalidated.

See also secsTo() and elapsed().

qint64 QElapsedTimer::nsecsElapsed() const

Returns the number of nanoseconds since this QElapsedTimer was last started. Calling this function in a QElapsedTimer that was invalidated will result in undefined results.

Epoch ravine (alpha) mac os. On platforms that do not provide nanosecond resolution, the value returned will be the best estimate available.

Mac Os Versions

This function was introduced in Qt 4.8.

See also start(), restart(), hasExpired(), and invalidate().

qint64 QElapsedTimer::restart()

Restarts the timer and returns the time 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.

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:

See also start(), invalidate(), and elapsed().

Elapsed Time Mac Os Catalina

qint64 QElapsedTimer::secsTo(const QElapsedTimer & other) const

Returns the number of seconds between this QElapsedTimer and other. If other was started before this object, the returned value will be positive. If it was started later, the returned value will be negative.

The return value is undefined if this object or other were invalidated.

See also msecsTo() and elapsed().

void QElapsedTimer::start()

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:

Also, starting a timer makes it valid again. How to run google drive on pc.

See also restart(), invalidate(), and elapsed().

bool QElapsedTimer::operator!=(const QElapsedTimer & other) const

Returns true if this object and other contain different times. Meridian coil mac os.

bool QElapsedTimer::operator(const QElapsedTimer & other) const

Returns true if this object and other contain the same time.

Elapsed Time Mac Os Catalina

© 2016 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.

Sending feedback…

We're sorry, an error has occurred.

Please try submitting your feedback later. https://trustnewline.weebly.com/jumper-surviour-mac-os.html.

Mac Os Download

Thank you for providing feedback!

Your input helps improve our developer documentation.