如何创建常驻线程以及waitUntilDone参数的作用

#import "ViewController.h"

@interface ViewController ()

@property (nonatomic, strong)NSThread *thread;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self createThread];
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    // waitUntilDone设置为YES,会阻塞主线程,优先在子线程中执行task2方法,task2方法执行完后主线程再继续后面的打印
    // waitUntilDone设置为NO,子线程的task2方法和主线程的打印同时进行
    [self performSelector:@selector(task2) onThread:self.thread withObject:nil
            waitUntilDone:YES];
    
    NSLog(@"cukiy1--%@",[NSThread currentThread]);
    NSLog(@"cukiy2--%@",[NSThread currentThread]);
    NSLog(@"cukiy3--%@",[NSThread currentThread]);
    NSLog(@"cukiy4--%@",[NSThread currentThread]);
    NSLog(@"cukiy5--%@",[NSThread currentThread]);
    NSLog(@"----------");
}


- (void)createThread
{
    // 创建子线程执行任务
    NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(task1) object:nil];
    [thread start];
    
    self.thread = thread;
}

- (void)task1
{
    NSLog(@"task1--%@",[NSThread currentThread]);
    
    // 子线程对应的runloop需要自己创建并开启
    // 创建子线程对应的runloop,使子线程一直存在
    NSRunLoop *currentRunloop = [NSRunLoop currentRunLoop];
    // 给runloop添加一个基于port的事件(系统事件),让runloop的运行模式不为空,保证runloop不退出
    [currentRunloop addPort:[NSPort port] forMode:NSDefaultRunLoopMode];
    // 开启运行循环
    [currentRunloop run];
}

- (void)task2
{
//    sleep(3);
    NSLog(@"task2-1-%@",[NSThread currentThread]);
    NSLog(@"task2-2-%@",[NSThread currentThread]);
    NSLog(@"task2-3-%@",[NSThread currentThread]);
    NSLog(@"task2-4-%@",[NSThread currentThread]);
}

@end