GCD的其他方法

1.栅栏函数

　　作用:控制线程的执行顺序

　　注:栅栏函数不能使用全局并发队列

 -(void)barrier
 {
     //1.创建队列(并发队列)
     dispatch_queue_t queue = dispatch_queue_create("com.downloadqueue", DISPATCH_QUEUE_CONCURRENT);

     dispatch_async(queue, ^{

         for (NSInteger i = ; i<; i++) {
             NSLog(@"%zd-download1--%@",i,[NSThread currentThread]);
         }
     });

     dispatch_async(queue, ^{

         for (NSInteger i = ; i<; i++) {
             NSLog(@"%zd-download2--%@",i,[NSThread currentThread]);
         }
     });

     //栅栏函数
     dispatch_barrier_async(queue, ^{
         NSLog(@"我是一个栅栏函数");
     });

     dispatch_async(queue, ^{

         for (NSInteger i = ; i<; i++) {
             NSLog(@"%zd-download3--%@",i,[NSThread currentThread]);
         }
     });

     dispatch_async(queue, ^{

         for (NSInteger i = ; i<; i++) {
             NSLog(@"%zd-download4--%@",i,[NSThread currentThread]);
         }
     });
 }

栅栏函数

2.延迟执行

 -(void)delay
 {
     NSLog(@"----");
     //表名2秒钟之后调用run
 //    [self performSelector:@selector(run) withObject:nil afterDelay:2.0];

 //    [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(run) userInfo:nil repeats:YES];

     /*
      第一个参数:延迟时间
      第二个参数:要执行的代码
      */
     dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_global_queue(, ), ^{
         NSLog(@"---%@",[NSThread currentThread]);
     });

 }

延迟执行

3.一次性代码

程序运行过程中只执行一次,执行一次后永远都不执行

 -(void)once
 {
     static dispatch_once_t onceToken;
     dispatch_once(&onceToken, ^{
         NSLog(@"+++++++++");
     });
 }

一次性代码

4.快速迭代

 -(void)applay
 {
 //    for (NSInteger i=0; i<10; i++) {
 //        NSLog(@"%zd--%@",i,[NSThread currentThread]);
 //    }

     //创建队列(并发队列)
     dispatch_queue_t queue = dispatch_queue_create("com.downloadqueue", DISPATCH_QUEUE_CONCURRENT);
     /*
      第一个参数:迭代的次数
      第二个参数:在哪个队列中执行
      第三个参数:block要执行的任务
      */
     dispatch_apply(, queue, ^(size_t index) {
         NSLog(@"%zd--%@",index,[NSThread currentThread]);
     });
 }

快速迭代

     //文件在哪个地方(文件夹)

     NSString *form = @"/Users/xiaomage/Desktop/form";

     //要剪切到什么地方

     NSString *to = @"/Users/xiaomage/Desktop/to";

 NSFileManager *manager = [NSFileManager defaultManager];

 //获取文件夹下子文件/子文件夹的路径

 //可以获取到子文件和子文件夹的路径

     NSArray *subpaths =  [manager subpathsAtPath:form];

 //   可以获取到子文件和子文件夹的路径
 NSDirectoryEnumerator *enumer = [manager enumeratorAtPath:to];

 //只能获取子文件的路径

     NSDirectoryEnumerator *enumer = [manager directoryContentsAtPath:form];

  //创建队列(并发队列)

     dispatch_queue_t queue = dispatch_queue_create("com.downloadqueue", DISPATCH_QUEUE_CONCURRENT);

     NSInteger count = [subpaths count];

     dispatch_apply(count, queue, ^(size_t index) {

         NSString *subpath = subpaths[index];

         NSString *fullPath = [form stringByAppendingPathComponent:subpath];

         //拼接目标文件全路径

         NSString *fileName = [to stringByAppendingPathComponent:subpath];

         //剪切操作

         [manager moveItemAtPath:fullPath toPath:fileName error:nil];

         NSLog(@"%@",[NSThread currentThread]);

     });

用快速迭代实现文件夹内容的转移

5.队列组

有这么1种需求

首先：分别异步执行2个耗时的操作

其次：等2个异步操作都执行完毕后，再回到主线程执行操作

 -(void)group
 {
     //下载图片1

     //创建队列组
     dispatch_group_t group =  dispatch_group_create();

     //1.开子线程下载图片
     //创建队列(并发)
     dispatch_queue_t queue = dispatch_get_global_queue(, );

     dispatch_group_async(group, queue, ^{
         //1.获取url地址
         NSURL *url = [NSURL URLWithString:@"http://www.huabian.com/uploadfile/2015/0914/20150914014032274.jpg"];

         //2.下载图片
         NSData *data = [NSData dataWithContentsOfURL:url];

         //3.把二进制数据转换成图片
         self.image1 = [UIImage imageWithData:data];

         NSLog(@"1---%@",self.image1);
     });

     //下载图片2
     dispatch_group_async(group, queue, ^{
         //1.获取url地址
         NSURL *url = [NSURL URLWithString:@"http://img1.3lian.com/img2011/w12/1202/19/d/88.jpg"];

         //2.下载图片
         NSData *data = [NSData dataWithContentsOfURL:url];

         //3.把二进制数据转换成图片
         self.image2 = [UIImage imageWithData:data];
         NSLog(@"2---%@",self.image2);

     });

     //合成
     dispatch_group_notify(group, queue, ^{

         //开启图形上下文
         UIGraphicsBeginImageContext(CGSizeMake(, ));

         //画1
         [self.image1 drawInRect:CGRectMake(, , , )];

         //画2
         [self.image2 drawInRect:CGRectMake(, , , )];

         //根据图形上下文拿到图片
         UIImage *image =  UIGraphicsGetImageFromCurrentImageContext();

         //关闭上下文
         UIGraphicsEndImageContext();

         dispatch_async(dispatch_get_main_queue(), ^{
             self.imageView.image = image;
             NSLog(@"%@--刷新UI",[NSThread currentThread]);
         });
     });
 }

用队列组合成网络上的两个图片