1、多線程的概念
Multithreading多線程是指從軟件或硬件上,實現多個線程併發執行的技術。使得能夠同步完成多項任務,提高資源使用效率。
1.1 任務、進程和線程
- 任務Task:應用程序完成的一個活動,一個task既可以是一個進程,也可以是一個線程;
- 進程Process:系統進行資源分配和調度的一個獨立單位,在內存中有完備的數據空間和代碼空間;
- 線程Thread:進程中的一個實體,CPU調度和分派的基本單位;
1.2 線程的Stack space
系統中每一個進程都有自己的內存空間,同個進程中多個線程共用進程的內存空間。
- 在Mac OS中,主線程的棧空間爲8MB;
- 在Ios中,主線程的棧空間爲1MB;
應用程序子線程默認棧空間大小爲512KB,子線程允許分配的最小棧空間爲16KB,並且必須是4KB的整數倍。開發者可以通過NSThread線程對象的stacksize來修改一個子線程的棧空間。
let thread = Thread.init(target: self, selector:(VIewController.threadAction),object:nil)
thread.stackSize = 1024*1024
- threadPriority: 0.0-1.0
- 系統默認優先級是0.5
- 高優先級並不是100%比低優先級先執行,只是得到CPU調度的紀律更高
- 創建 對線程對象進行初始化;
- 就緒 添加到線程池,等待CPU的調度;
- 運行 是線程處於執行狀態;
- 阻塞 可以是線程休眠至指定的時間點,或者通過Lock給線程加鎖;
- 消亡 執行完畢之後自動處於正常消亡狀態;
var imageView = UIImageView()
var label = UILabel()
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
imageView = UIImageView(frame: CGRect(x: 0, y: 120, width: 320, height: 300))
self.view.addSubview(imageView)
label = UILabel(frame: CGRect(x: 0, y: 120, width: 320, height: 300))
label.backgroundColor = UIColor.lightGray
label.textAlignment = .center
label.text = "Loading..."
label.font = UIFont.systemFont(ofSize: 42)
self.view.addSubview(label)
let imageUrl = "http://images.apple.com/v/iphone/home/s/home/images/trade_in_iphone_large_2x.jpg"
let thread = Thread(target: self, selector: #selector(ViewController.downloadImage), object: imageUrl)
thread.start()
}
func downloadImage(path : String){
let url = URL(string: path)
var data : Data!
do{
try data = Data(contentsOf: url!)
let image = UIImage(data: data)
self.perform(#selector(ViewController.showImage), on: Thread.main, with: image, waitUntilDone: true)
}catch{
print("下載圖片失敗。")
}
}
func showImage(image : UIImage){
self.imageView.image = image
self.label.isHidden = true
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
topImageView = UIImageView(frame: CGRect(x: 0, y: 0, width: 320, height: 280))
self.view.addSubview(topImageView)
footImageView = UIImageView(frame: CGRect(x: 0, y: 280, width: 320, height: 290))
self.view.addSubview(footImageView)
let downloadA = getOperation(name: "下載線程A", imageUrl: "http://images.apple.com/v/watch/k/images/overview/watch_03_large.jpg", isTopOne: true)
let downloadB = getOperation(name: "下載線程B", imageUrl: "http://images.apple.com/v/watch/k/images/overview/watch_05_large.jpg", isTopOne: false)
let queue = OperationQueue()
queue.maxConcurrentOperationCount = 1
queue.addOperation(downloadA)
queue.addOperation(downloadB)
for operation in queue.operations{
print("Operation名稱:"+operation.name!)
}
}
func getOperation(name : String, imageUrl : String, isTopOne : Bool) -> BlockOperation{
let download = BlockOperation(block: {_ in
let url = URL(string: imageUrl)
var data : Data!
do{
Thread.sleep(forTimeInterval: 1.0)
try data = Data(contentsOf: url!)
let image = UIImage(data: data)
if isTopOne{
self.perform(#selector(ViewController.showTopImage), on: Thread.main, with: image, waitUntilDone: true)
}
else{
self.perform(#selector(ViewController.showFootImage), on: Thread.main, with: image, waitUntilDone: true)
}
}catch{
print("下載圖片失敗。")
}
})
download.name = name
return download
}
func showTopImage(image : UIImage){
self.topImageView.image = image
}
func showFootImage(image : UIImage){
self.footImageView.image = image
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
label.frame = CGRect(x: 0, y: 0, width: 320, height: 568)
label.text = "Loading..."
label.font = UIFont(name: "Arial", size: 24)
label.backgroundColor = UIColor.orange
label.numberOfLines = 0
label.lineBreakMode = NSLineBreakMode.byWordWrapping
self.view.addSubview(label)
let apiURL = URL(string: "http://ip.taobao.com/service/getIpInfo.php?ip=27.156.152.57")
let globalQueue = DispatchQueue.global()
globalQueue.async{
let result = try? Data(contentsOf: apiURL!)
let message = String(data: result!, encoding: String.Encoding.utf8)
DispatchQueue.main.async
{
self.label.text = message
}
}
}
3、總結
- Thread(基於thread):每個Thread對象對應一個線程,優點是量級較輕,使用簡單,缺點是需要開發者自行管理線程的生命週期、線程同步、加鎖解鎖、睡眠以及喚醒等操作。
- Operation(基於queue):不需要關心線程的管理和線程同步的事情,可以把精力放在自己需要執行的業務邏輯上,缺點是隻能實現它或者使用它定義好的子類。
- Grand Central Dispatch(task):基於C語言的一種高效、強大的多核編輯解決方案,其在後端管理着一個線程池,它不僅僅決定代碼塊將在那個線程被執行,還可以根據可用的系統資源對這些線程進行管理。