Struct qt_core::q_elapsed_timer::ClockType
source · pub struct ClockType(/* private fields */);Expand description
This enum contains the different clock types that QElapsedTimer may use.
C++ 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 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' 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.
MachAbsoluteTime
This clock type is based on the absolute time presented by Mach kernels, such as that found on macOS. This clock type is presented separately from MonotonicClock since macOS and iOS are also Unix systems 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().
Implementations§
source§impl ClockType
impl ClockType
sourcepub const SystemTime: ClockType = _
pub const SystemTime: ClockType = _
The human-readable system time. This clock is not monotonic. (C++ enum variant: SystemTime = 0)
sourcepub const MonotonicClock: ClockType = _
pub const MonotonicClock: ClockType = _
The system’s monotonic clock, usually found in Unix systems. This clock is monotonic and does not overflow. (C++ enum variant: MonotonicClock = 1)
sourcepub const TickCounter: ClockType = _
pub const TickCounter: ClockType = _
The system’s tick counter, used on Windows systems. This clock may overflow. (C++ enum variant: TickCounter = 2)
sourcepub const MachAbsoluteTime: ClockType = _
pub const MachAbsoluteTime: ClockType = _
The Mach kernel’s absolute time (macOS and iOS). This clock is monotonic and does not overflow. (C++ enum variant: MachAbsoluteTime = 3)
sourcepub const PerformanceCounter: ClockType = _
pub const PerformanceCounter: ClockType = _
The high-resolution performance counter provided by Windows. This clock is monotonic and does not overflow. (C++ enum variant: PerformanceCounter = 4)