刚学线程通信，提示：

2016-01-27 11:11:02.246 20-9 gcd3 communicationOfThread[5193:298643] App Transport Security has blocked a cleartext HTTP (http://) resource load since it is insecure. Temporary exceptions can be configured via your app's Info.plist file.

原来是因为 iOS9之后，原http协议被改成了https协议，使用 TLS1.2 SSL加密请求数据。

在info.plist中添加
<key>NSAppTransportSecurity</key><dict>
    <key>NSAllowsArbitraryLoads</key>
    <true/></dict>

即可

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(queue, ^{
        NSLog(@"url:%@",[NSThread currentThread]);
        NSURL *url = [NSURL URLWithString:@"http://www.cechina.cn/upload/article/adc81d83-4603-4e1c-a116-9325e89cd309/s1.jpg"];
        NSData *data = [NSData dataWithContentsOfURL:url];
        UIImage *image = [UIImage imageWithData:data];
        NSLog(@"url:%@,image:%@",[NSThread currentThread],image);

dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"downLoad:%@,image:%@",[NSThread currentThread],image);

[self.btn setBackgroundImage:image  forState:UIControlStateNormal];
        });
    });
    
}