OperationQueue sample

Playground.swift

import UIKit

final class SampleOperation: Operation {
    let message: String

    init(message: String) {
        self.message = message
    }

    override func main() {
        if isCancelled {
            return
        }
        sleep(10)
        print("\(message) \(Date().timeIntervalSince1970)")
    }
}

let sample1 = SampleOperation(message: "foo")
let sample2 = SampleOperation(message: "bar")
let sample3 = SampleOperation(message: "hoge")

let queue = OperationQueue()
// 実行数を1にする
queue.maxConcurrentOperationCount = 1

// queueに追加すると順次実行される
queue.addOperation(sample1)
queue.addOperation(sample2)
if sample1.isExecuting {
    // sample1のOperationが実行中なら、sample2をキャンセルする
    sample2.cancel()
}
queue.addOperation(sample3)

/*
 実行結果
 foo 1611583657.37749
 hoge 1611583667.378951
 */