1. NSThread的三種創(chuàng)建方法

    //方式一 對(duì)象方法
    NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(test) object:nil];
    //線程名稱
    //作用：可以快速找到出錯(cuò)的線程
    thread.name = @"test";
    //優(yōu)先級(jí)0-1，默認(rèn)0.5
    //優(yōu)先級(jí)高代表cpu在該線程調(diào)度所用的時(shí)間多
    thread.threadPriority = 1.0;
    [thread start];
    
    //方式二 類方法
    [NSThread detachNewThreadSelector:@selector(test) toTarget:self withObject:nil];
    
    //方式三
    [self performSelectorInBackground:@selector(test) withObject:nil];

- (void)test {
    NSLog(@"%@",[NSThread currentThread]);
}

2.NSThread的幾種狀態(tài)

新建-就緒-運(yùn)行-阻塞-銷毀

//新建
NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(test) object:nil];
//就緒
 [thread start];

- (void)test {
    //線程運(yùn)行是由cpu控制的，結(jié)束之后會(huì)自動(dòng)銷毀
    //下面是模擬狀態(tài)
    for (int i = 0; i < 20; i ++) {
        if (i == 5) {
            //線程阻塞
            [NSThread sleepForTimeInterval:2.0];
        }
        if (i == 10) {
            //線程主動(dòng)銷毀
            [NSThread exit];
        }
    }
}

3.線程的資源共享（不安全）

舉例：賣火車票，票數(shù)總共10張，兩個(gè)窗口同時(shí)賣
代碼檢驗(yàn)：

    @property (nonatomic, assign) NSInteger ticketsCount;//總票數(shù)

    self.ticketsCount = 10;
    
    //創(chuàng)建二個(gè)線程
    NSThread *thread1 = [[NSThread alloc] initWithTarget:self selector:@selector(sellTickets) object:nil];
    [thread1 start];
    
    NSThread *thread2 = [[NSThread alloc] initWithTarget:self selector:@selector(sellTickets) object:nil];
    [thread2 start];

- (void)sellTickets {
    while (1) {
        //模擬耗時(shí)
        [NSThread sleepForTimeInterval:1.0];
        if (self.ticketsCount > 0) {
            self.ticketsCount--;
            NSLog(@"剩余%ld張",self.ticketsCount);
        } else {
            NSLog(@"票已賣完");
            break;
        }
    }
}

輸出結(jié)果：從以下圖中可以看出輸出是無(wú)序的，讀寫出錯(cuò)，也就是線程不安全

D8D06852-22FE-4539-9189-CD66D7391799.png

解決方案：給數(shù)據(jù)的讀寫操作加把互斥鎖

- (void)sellTickets {
    while (1) {
        //模擬耗時(shí)
        [NSThread sleepForTimeInterval:1.0];
        //同步
        //默認(rèn)打開(kāi)鎖，進(jìn)入之后會(huì)關(guān)閉鎖，直到結(jié)束才打開(kāi)鎖
        @synchronized (self) {
            if (self.ticketsCount > 0) {
                self.ticketsCount--;
                NSLog(@"剩余%ld張",self.ticketsCount);
            } else {
                NSLog(@"票已賣完");
                break;
            }
        }
    }
}

輸出效果：有序的執(zhí)行，保證了線程的安全，但是性能會(huì)降低

image.png