iOS開發多線程（二） NSThread的使用（轉）

時間 2019-11-13

原文原文鏈接

每一個iOS應用程序都有個專門用來更新顯示UI界面、處理用戶的觸摸事件的主線程，所以不能將其餘太耗時的操做放在主線程中執行，否則會形成主線程堵塞(出現卡機現象)，帶來極壞的用戶體驗。通常的解決方案就是將那些耗時的操做放到另一個線程中去執行，多線程編程是防止主線程堵塞，增長運行效率的最佳方法java

iOS支持多個層次的多線程編程，層次越高的抽象程度越高，使用也越方便，也是蘋果最推薦使用的方法。下面根據抽象層次從低到高依次列出iOS所支持的多線程編程方法：編程

1.Thread ：是三種方法裏面相對輕量級的，但須要管理線程的生命週期、同步、加鎖問題，這會致使必定的性能開銷
2.Cocoa Operations：是基於OC實現的，NSOperation以面向對象的方式封裝了須要執行的操做，沒必要關心線程管理、同步等問題。NSOperation是一個抽象基類，iOS提供了兩種默認實現：NSInvocationOperation和NSBlockOperation，固然也能夠自定義NSOperation
3.Grand Central Dispatch(簡稱GCD，iOS4纔開始支持)：提供了一些新特性、運行庫來支持多核並行編程，它的關注點更高：如何在多個cpu上提高效率
多線程

這篇文章簡單介紹了第一種多線程編程的方式，主要是利用NSThread這個類，一個NSThread實例表明着一條線程app

1、NSthread的初始化ide

1.動態方法性能

[java] view plain copyatom

- (id)initWithTarget:(id)target selector:(SEL)selector object:(id)argument; spa

[java] view plain copy.net

// 初始化線程線程
NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
// 設置線程的優先級(0.0 - 1.0，1.0最高級)
thread.threadPriority = 1;
// 開啓線程
[thread start];

參數解析：

selector ：線程執行的方法，這個selector最多隻能接收一個參數
target ：selector消息發送的對象
argument : 傳給selector的惟一參數，也能夠是nil

2.靜態方法

[java] view plain copy

+ (void)detachNewThreadSelector:(SEL)selector toTarget:(id)target withObject:(id)argument;

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[NSThread detachNewThreadSelector:@selector(run) toTarget:self withObject:nil];
// 調用完畢後，會立刻建立並開啓新線程

3.隱式建立線程的方法

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[self performSelectorInBackground:@selector(run) withObject:nil];

2、獲取當前線程

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NSThread *current = [NSThread currentThread];

3、獲取主線程

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NSThread *main = [NSThread mainThread];

4、暫停當前線程

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// 暫停2s
[NSThread sleepForTimeInterval:2];
// 或者
NSDate *date = [NSDate dateWithTimeInterval:2 sinceDate:[NSDate date]];
[NSThread sleepUntilDate:date];

5、線程間的通訊

1.在指定線程上執行操做

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[self performSelector:@selector(run) onThread:thread withObject:nil waitUntilDone:YES];

2.在主線程上執行操做

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[self performSelectorOnMainThread:@selector(run) withObject:nil waitUntilDone:YES];

3.在當前線程執行操做

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[self performSelector:@selector(run) withObject:nil];

6、優缺點

1.優勢：NSThread比其餘兩種多線程方案較輕量級，更直觀地控制線程對象

2.缺點：須要本身管理線程的生命週期，線程同步。線程同步對數據的加鎖會有必定的系統開銷

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--------------另一個博客的補充----------

2.3 線程同步

咱們演示一個經典的賣票的例子來說NSThread的線程同步：

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#import <UIKit/UIKit.h>
@class ViewController;
@interface AppDelegate : UIResponder <UIApplicationDelegate>
{
int tickets;
int count;
NSThread* ticketsThreadone;
NSThread* ticketsThreadtwo;
NSCondition* ticketsCondition;
NSLock *theLock;
}
@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) ViewController *viewController;
@end

[cpp] view plain copy

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
tickets = 100;
count = 0;
theLock = [[NSLock alloc] init];
// 鎖對象
ticketsCondition = [[NSCondition alloc] init];
ticketsThreadone = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
[ticketsThreadone setName:@"Thread-1"];
[ticketsThreadone start];
ticketsThreadtwo = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
[ticketsThreadtwo setName:@"Thread-2"];
[ticketsThreadtwo start];
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
self.window.rootViewController = self.viewController;
[self.window makeKeyAndVisible];
return YES;
}
- (void)run{
while (TRUE) {
// 上鎖
// [ticketsCondition lock];
[theLock lock];
if(tickets >= 0){
[NSThread sleepForTimeInterval:0.09];
count = 100 - tickets;
NSLog(@"當前票數是:%d,售出:%d,線程名:%@",tickets,count,[[NSThread currentThread] name]);
tickets--;
}else{
break;
}
[theLock unlock];
// [ticketsCondition unlock];
}
}

若是沒有線程同步的lock，賣票數多是-1.加上lock以後線程同步保證了數據的正確性。
上面例子我使用了兩種鎖，一種NSCondition ，一種是：NSLock。 NSCondition我已經註釋了。

線程的順序執行

他們均可以經過

[ticketsCondition signal]; 發送信號的方式，在一個線程喚醒另一個線程的等待。

好比：

[cpp] view plain copy

#import "AppDelegate.h"
#import "ViewController.h"
@implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
tickets = 100;
count = 0;
theLock = [[NSLock alloc] init];
// 鎖對象
ticketsCondition = [[NSCondition alloc] init];
ticketsThreadone = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
[ticketsThreadone setName:@"Thread-1"];
[ticketsThreadone start];
ticketsThreadtwo = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
[ticketsThreadtwo setName:@"Thread-2"];
[ticketsThreadtwo start];
NSThread *ticketsThreadthree = [[NSThread alloc] initWithTarget:self selector:@selector(run3) object:nil];
[ticketsThreadthree setName:@"Thread-3"];
[ticketsThreadthree start];
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
self.window.rootViewController = self.viewController;
[self.window makeKeyAndVisible];
return YES;
}
-(void)run3{
while (YES) {
[ticketsCondition lock];
[NSThread sleepForTimeInterval:3];
[ticketsCondition signal];
[ticketsCondition unlock];
}
}
- (void)run{
while (TRUE) {
// 上鎖
[ticketsCondition lock];
[ticketsCondition wait];
[theLock lock];
if(tickets >= 0){
[NSThread sleepForTimeInterval:0.09];
count = 100 - tickets;
NSLog(@"當前票數是:%d,售出:%d,線程名:%@",tickets,count,[[NSThread currentThread] name]);
tickets--;
}else{
break;
}
[theLock unlock];
[ticketsCondition unlock];
}
}

wait是等待，我加了一個線程3 去喚醒其餘兩個線程鎖中的wait

其餘同步

咱們可使用指令 @synchronized 來簡化 NSLock的使用，這樣咱們就沒必要顯示編寫建立NSLock,加鎖並解鎖相關代碼。- (void)doSomeThing:(id)anObj{ @synchronized(anObj) { // Everything between the braces is protected by the @synchronized directive. }}