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

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?