iOS中的多线程

都是些基本的东西，但是温故而知新哈

iOS中有三种多线程编程的技术分别是：

• NSThread

• NSOperation（NSOperation 和 NSOperationQueue）

• GCD

• NSThread
  优点：NSThread 比其他两个轻量级。
  缺点：需要自己管理线程的生命周期，线程同步对数据的加锁会有一定的系统开销。

    // 第一种 直接创建新线程并且开始运行线程
    [NSThread detachNewThreadSelector:@selector(myThread:) toTarget:self withObject:nil];

    // 第二种 先创建新线程，再运行操作，在运行操作前可以设置线程优先级等相关信息
    NSThread *myThread = [[NSThread alloc] initWithTarget:self selector:@selector(myThread:) object:nil];
    [myThread start];

     // 第三种 隐式创建
    [self performSelectorInBackground:@selector(myThread:) withObject:nil];

// 使用NSThread写一个经典的卖票的例子来讲线程同步
- (void)syncThread {
    // 初始化总票数
    self.tickes = 100;
    // 初始化锁对象
    self.myLock = [[NSLock alloc] init];
    // 创建两个线程，模拟网上售票和站台售票
    NSThread *onlineThread = [[NSThread alloc] initWithTarget:self selector:@selector(sellTickes) object:nil];
    onlineThread.name = @"网上售票口";
    [onlineThread start];

    NSThread *stationThread = [[NSThread alloc] initWithTarget:self selector:@selector(sellTickes) object:nil];
    stationThread.name = @"站点售票口";
    [stationThread start];
}
- (void)sellTickes {
    while (true) {
        // 加锁
        [self.myLock lock];
        // 模拟网络堵塞
        [NSThread sleepForTimeInterval:1];
        if (self.tickes > 0) {
            self.tickes -= 1;
            NSLog(@"当前售票口是:%@, 余票%d张。", [[NSThread currentThread] name], self.tickes);
        }else{
            NSLog(@"亲，你来晚了，票卖完了！");
            break;
        }
        // 解锁
        [self.myLock unlock];

    }
}

• NSOperation的使用方法有两种
  一种是使用定义好的两个子类： NSInvocationOperation 和 NSBlockOperation
  第二种是继承NSOperation

- (void)testNSOperation {
    // 使用定义好的两个子类
    NSInvocationOperation *operation1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(test) object:nil];
    operation1.name = @"operation1";

    NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"blockOperation %@", [NSThread currentThread]);
    }];
    blockOperation.name = @"blockOperation";

    // 把NSOperation子类放入队列中去
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    [queue addOperation:operation1];
    [queue addOperation:blockOperation];
    queue.maxConcurrentOperationCount = 2; // 最大并发数
}
- (void)test {
    NSLog(@"invocationOperation %@", [NSThread currentThread]);
}

• GCD
  GCD的底层依然使用线程实现的，可以让程序员不用关注细节
  GCD中的队列称为dispath queue，有两种一是串行队列，一是并行队列。

执行的时候，又分为同步（不开子线程）和异步（开子线程）

/** 异步-全局并发 */
- (IBAction)async1 {
    // 获得全局并发队列（常用就是这个）
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(queue, ^{
        NSLog(@"1 = %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"2 = %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"3 = %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"4 = %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"5 = %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"6 = %@", [NSThread currentThread]);
    });

    /*
     打印结果
     2016-03-08 13:26:13.109 NSThreadDemo[38192:1073138] 2 = {number = 3, name = (null)}
     2016-03-08 13:26:13.109 NSThreadDemo[38192:1073139] 3 = {number = 4, name = (null)}
     2016-03-08 13:26:13.109 NSThreadDemo[38192:1073140] 1 = {number = 2, name = (null)}
     2016-03-08 13:26:13.109 NSThreadDemo[38192:1073586] 5 = {number = 6, name = (null)}
     2016-03-08 13:26:13.109 NSThreadDemo[38192:1073585] 4 = {number = 5, name = (null)}
     2016-03-08 13:26:13.110 NSThreadDemo[38192:1073138] 6 = {number = 3, name = (null)}
     */
}

/** 异步-串行 */
- (IBAction)async2 {
    // 自己创建一个队列
    dispatch_queue_t queue = dispatch_queue_create("liyang", NULL);
    dispatch_async(queue, ^{
        NSLog(@"1 = %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"2 = %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"3 = %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"4 = %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"5 = %@", [NSThread currentThread]);
    });
    dispatch_async(queue, ^{
        NSLog(@"6 = %@", [NSThread currentThread]);
    });

    /*
     打印结果
     2016-03-08 13:26:42.443 NSThreadDemo[38192:1078469] 1 = {number = 7, name = (null)}
     2016-03-08 13:26:42.443 NSThreadDemo[38192:1078469] 2 = {number = 7, name = (null)}
     2016-03-08 13:26:42.443 NSThreadDemo[38192:1078469] 3 = {number = 7, name = (null)}
     2016-03-08 13:26:42.444 NSThreadDemo[38192:1078469] 4 = {number = 7, name = (null)}
     2016-03-08 13:26:42.444 NSThreadDemo[38192:1078469] 5 = {number = 7, name = (null)}
     2016-03-08 13:26:42.444 NSThreadDemo[38192:1078469] 6 = {number = 7, name = (null)}
     */
}

/** 同步-并发 */
- (IBAction)sync1 {
    // 获得全局并发队列（常用就是这个）
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_sync(queue, ^{
        NSLog(@"1 = %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"2 = %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"3 = %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"4 = %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"5 = %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"6 = %@", [NSThread currentThread]);
    });
    /*
     打印结果
     2016-03-08 13:27:37.110 NSThreadDemo[38192:1072944] 1 = {number = 1, name = main}
     2016-03-08 13:27:37.110 NSThreadDemo[38192:1072944] 2 = {number = 1, name = main}
     2016-03-08 13:27:37.110 NSThreadDemo[38192:1072944] 3 = {number = 1, name = main}
     2016-03-08 13:27:37.110 NSThreadDemo[38192:1072944] 4 = {number = 1, name = main}
     2016-03-08 13:27:37.110 NSThreadDemo[38192:1072944] 5 = {number = 1, name = main}
     2016-03-08 13:27:37.111 NSThreadDemo[38192:1072944] 6 = {number = 1, name = main}
     */
}

/** 同步-串行 */
- (IBAction)sync2 {
    // 自己创建一个队列
    dispatch_queue_t queue = dispatch_queue_create("liyang", NULL);
    dispatch_sync(queue, ^{
        NSLog(@"1 = %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"2 = %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"3 = %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"4 = %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"5 = %@", [NSThread currentThread]);
    });
    dispatch_sync(queue, ^{
        NSLog(@"6 = %@", [NSThread currentThread]);
    });
    /*
     打印结果
     2016-03-08 13:28:06.597 NSThreadDemo[38192:1072944] 1 = {number = 1, name = main}
     2016-03-08 13:28:06.597 NSThreadDemo[38192:1072944] 2 = {number = 1, name = main}
     2016-03-08 13:28:06.597 NSThreadDemo[38192:1072944] 3 = {number = 1, name = main}
     2016-03-08 13:28:06.597 NSThreadDemo[38192:1072944] 4 = {number = 1, name = main}
     2016-03-08 13:28:06.597 NSThreadDemo[38192:1072944] 5 = {number = 1, name = main}
     2016-03-08 13:28:06.597 NSThreadDemo[38192:1072944] 6 = {number = 1, name = main}
     */
}

PS: 网址 https://github.com/liyang123/iOS-.git