swift iOS / OSX / Swift中的精确计时

Posted 2021-05-19

//: Playground - noun: a place where code can play

import UIKit

//Most precise time keeper
// for more information on the benchmarks go to www.kandelvijaya.com

func timeBlockWithMach(_ block: () -> Void) -> TimeInterval {
    var info = mach_timebase_info()
    guard mach_timebase_info(&info) == KERN_SUCCESS else { return -1 }
    
    let start = mach_absolute_time()
    block()
    let end = mach_absolute_time()
    
    let elapsed = end - start
    
    let nanos = elapsed * UInt64(info.numer) / UInt64(info.denom)
    return TimeInterval(nanos) / TimeInterval(NSEC_PER_SEC)
}


func test() {
    let rtDate = timeBlockWithMach{
        NSDate().timeIntervalSince1970
    }
    
    let rtMedia =  timeBlockWithMach {
        CACurrentMediaTime()
    }
    
    let rtAbsolute = timeBlockWithMach {
        CFAbsoluteTimeGetCurrent()
    }
    
    var time = timeval()
    let rtTimeOfDay = timeBlockWithMach {
        gettimeofday(&time, nil)
    }
    
    let rtTimeWithMach = timeBlockWithMach {
        mach_absolute_time()
    }
    
    let rtTimeWithProcessInfo = timeBlockWithMach {
        ProcessInfo.processInfo.systemUptime
    }
}

test()


// MARK: - Other timing functions
func timeBlockWithDateTime(_ block: () -> Void) -> TimeInterval {
    let start = NSDate().timeIntervalSince1970
    block()
    let end = NSDate().timeIntervalSince1970
    return end - start
}

func timeBlockWithCAMediaTiming(_ block: () -> Void) -> TimeInterval {
    let start = CACurrentMediaTime()
    block()
    let end = CACurrentMediaTime()
    return end - start
}

func timeBlockWithCFTime(_ block: () -> Void) -> TimeInterval {
    let start = CFAbsoluteTimeGetCurrent()
    block()
    let end = CFAbsoluteTimeGetCurrent()
    return end - start
}

func timeBlockWithGetTimeOfDay(_ block: () -> Void) -> TimeInterval {
    var start = timeval()
    gettimeofday(&start, nil)
    block()
    var end = timeval()
    gettimeofday(&end, nil)
    
    return Double(start.tv_usec - end.tv_usec)
}