// 当创建一个线程，并且希望它一直存在时，但往往我们创建的线程都是执行完成之后也就停止了，不能再次利用，那么如何创建一个线程可以让他可以再次工作呢,这个时候就需要使用到RunLoop了。下面的是我写的一个例子：
#import "LongThreadDemoController.h"

@interface LongThreadDemoController ()

@property (nonatomic, strong) NSThread *thread;

@end

@implementation LongThreadDemoController

- (void)viewDidLoad {

    [super viewDidLoad];

    self.view.backgroundColor = [UIColor whiteColor];

    self.title = @"常驻线程Demo";

}

- (void)threadRunloopPoint:(id)__unused object{

    NSLog(@"%@",NSStringFromSelector(_cmd));

    @autoreleasepool {

        [[NSThread currentThread] setName:@"changzhuThread"];

        NSRunLoop *runLoop = [NSRunLoop currentRunLoop];

        //// 这里主要是监听某个 port，目的是让这个 Thread 不会回收

        [runLoop addPort:[NSMachPort port] forMode:NSDefaultRunLoopMode];

        [runLoop run];

    }

}

- (NSThread *)thread{

    if(!_thread){

        _thread = [[NSThread alloc] initWithTarget:self selector:@selector(threadRunloopPoint:) object:nil];

        [_thread start];

    }

    return _thread;

}

- (void)test{

    NSLog(@"%s",__func__);

}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{

    [self performSelector:@selector(test) onThread:self.thread withObject:nil waitUntilDone:NO modes:@[NSDefaultRunLoopMode]];

}