在IOS多线程中NSThread这种方式虽然简单易用，但是需要程序员管理，所以在实际开发中使用较少。这里只简单介绍。方便更好的理解GCD和NSOperation。

• NSThread创建

  //1.创建方式
  NSThread *thread = [[NSThread alloc] initWithTarget:self   selector:@selector(demo:) object:@"Thread"];
  //启动线程
  [thread start];
  //2.创建方式
  [NSThread detachNewThreadSelector:@selector(demo:) toTarget:self withObject:@"Detach"];
  //3.创建方式
  [self performSelectorInBackground:@selector(demo:) withObject:@"background"];
  

• 常用属性和方法

  //设置线程名字
  @property (nullable, copy) NSString *name
  //阻断
  + (void)sleepForTimeInterval:(NSTimeInterval)ti;
  //终止线程
  + (void)exit;
  //设置优先级
  + (BOOL)setThreadPriority:(double)p;
  

• 线程间的通讯方法

  //主线程
  - (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait modes:(nullable NSArray<NSString *> *)array;
  //主线程
  - (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait;
  //子线程
  - (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(nullable id)arg waitUntilDone:(BOOL)wait modes:(nullable NSArray<NSString *> *)array ;
  //子线程
  - (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(nullable id)arg waitUntilDone:(BOOL)wait 
  //子线程
  - (void)performSelectorInBackground:(SEL)aSelector withObject:(nullable id)arg ;
  

• 互斥锁
  互斥锁：保证锁内的代码，同一时间只有1个线程执行。
  互斥锁的范围：尽量要小，范围大，效率就会差。
  例子:

  self.tickets = 20;
  NSThread *t1 = [[NSThread alloc]initWithTarget:self selector:@selector(saleTickets) object:nil];
    t1.name = @"售票员B";
    [t1 start];
  
  NSThread *t2 = [[NSThread alloc]initWithTarget:self selector:@selector(saleTickets) object:nil];
    t2.name = @"售票员A";
    [t2 start];
  
  -(void)saleTickets
  {
      while (YES) {
        [NSThread sleepForTimeInterval:1.0];
        //这个地方添加互斥锁，保证买票的代码执行是在同一线程。
        @synchronized (self) {
            if (self.tickets > 0) {
                self.tickets--;
                NSLog(@"剩下%d张票 %@",self.tickets,[NSThread currentThread]);
            }else
            {
                NSLog(@"卖完了");
                break;
            }
        }    
    }    
  }