示意图.png

1、优缺点

1.优点：NSThread比其他两种多线程方案较轻量级，更直观地控制线程对象
2.缺点：需要自己管理线程的生命周期，线程同步。线程同步对数据的加锁会有一定的系统开销

2、 NSThread相关的主要方法：

创建、启动线程

  // 线程一启动，就会在线程thread中执行self的run方法

NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];

[thread start];

创建线程后自动启动线程

[NSThread detachNewThreadSelector:@selector(test) toTarget:self withObject:nil];

隐式创建并启动线程

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

3、互斥锁

@synchronized(锁对象) { // 需要锁定的代码 }

互斥锁的优缺点
优点：能有效防止因多线程抢夺资源造成的数据安全问题
缺点：需要消耗大量的CPU资源

互斥锁的使用前提：多条线程抢夺同一块资源

4、线程间通信

线程间通信常用方法

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait;

- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(id)arg waitUntilDone:(BOOL)wait;

5、模拟一个卖票系统

self.tickets = 100;//总共票数

NSThread *thread1 = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
thread1.name = @"售票机1";
[thread1 start];

NSThread *thread2 = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
thread2.name = @"售票机2";
[thread2 start];



- (void)run {

    if (_lock == nil)
    {
        _lock = [[NSLock alloc] init];
    }

    while (YES)
    {
        [_lock lock];
        if (_tickets > 0)
        {
            _tickets -= 1;
            NSString *message = [NSString stringWithFormat:@"当前票数是%ld，售票线程是%@",(long)_tickets,[[NSThread currentThread] name]];

            NSLog(@"message == %@",message);
        
            [_lock unlock];
        
            if ([[[NSThread currentThread] name] isEqualToString:@"售票机1"])
            {
                [NSThread sleepForTimeInterval:0.2];
            }
            else
                [NSThread sleepForTimeInterval:0.3];
        }
        else
        {
            [_lock unlock];
            break;
        }
    }
}