runloop 阻塞主线程

@implementation ViewController{
    BOOL end;
}
– (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@”start new thread …”);
    [NSThread detachNewThreadSelector:@selector(runOnNewThread) toTarget:self withObject:nil];
    while (!end) {
        NSLog(@”runloop…”);
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
        NSLog(@”runloop end.”);
    }
    NSLog(@”ok.”);
}

-(void)runOnNewThread{
    NSLog(@”run for new thread …”);
    sleep(1);
    [self performSelectorOnMainThread:@selector(setEnd) withObject:nil waitUntilDone:NO];
    NSLog(@”end.”);
}
-(void)setEnd{
    end=YES;
}