ios - Xcode instrument time profiler total time estimated wrong when using third party pods libraries

Question

I am using Xcode instrument time profiler to measure the performance of my app. At the same time, I am also using CFAbsoluteTimeGetCurrent function in my code to print the time I used. However, I have found that sometimes the execution time of a function measured by these two methods are the same, but sometimes there is a big difference.

Here is an example

import UIKit
import ZippyJSON

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    override func viewDidAppear(_ animated: Bool) {
        let encoder = JSONEncoder()
        var students = [Student]()
        var scores = [Int]()
        for _ in 0...100 {
            scores.append(99984)
        }
        for _ in 0...100 {
            students.append(Student(name: "StudentName", age: 99, scores: scores))
        }
        var dataList = [Data]()
        for _ in 0...100 {
            let data = try! encoder.encode(students)
            dataList.append(data)
        }
        testJson(dataList: dataList)
    }
}

func testJson(dataList: [Data]) {
    let t1 = CFAbsoluteTimeGetCurrent()
    let decoder = JSONDecoder()
    var results = [[Student]]()
    for data in dataList {
        let r1 = CFAbsoluteTimeGetCurrent()
        let result = try! decoder.decode([Student].self, from: data)
        let r2 = CFAbsoluteTimeGetCurrent()
        results.append(result)
        print("single time (r2 - r1)")
    }
    let t2 = CFAbsoluteTimeGetCurrent()
    print("total time (t2 - t1)")
}

At this time, I am using Apple's JSONDecoder to decode the data created by me. The printing of the program is

total time 1.428820013999939

And it corresponds to what Time Profiler produce

However, if I change to use a third party library ZippyJSONDecoder to decode the data

func testJson(dataList: [Data]) {
    let t1 = CFAbsoluteTimeGetCurrent()
    let decoder = ZippyJSONDecoder()
    var results = [[Student]]()
    for data in dataList {
        let r1 = CFAbsoluteTimeGetCurrent()
        let result = try! decoder.decode([Student].self, from: data)
        let r2 = CFAbsoluteTimeGetCurrent()
        results.append(result)
        print("single time (r2 - r1)")
    }
    let t2 = CFAbsoluteTimeGetCurrent()
    print("total time (t2 - t1)")
}

The printing of the program is

total time 3.199104905128479

But the Time Profile produces this result

It is only 325ms, totally different from what produces by the measurement of CFAbsoluteTimeGetCurrent

I am wondering why this problem occured? Which result is the correct one?

question from:https://stackoverflow.com/questions/65912772/xcode-instrument-time-profiler-total-time-estimated-wrong-when-using-third-party

Answer 1

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