GCD

1. dispatch_queue_create
   串行队列:先后顺序,依赖关系

• dispatch_get_global_queue
  并行队列:不存在任何依赖关系,提高执行速度
• dispatch_group_create
  分组任务:几个任务之间存在关系,最后一个任务依赖于前几个
• dispatch_once_t
  一次:只执行一次
• dispatch_barrier_async
  障碍:后几个需要前几个执行完,自己创建的队列,才能添加障碍,
• dispatch_after
  延迟: 需要延迟几秒
• dispatch_apply
  反复执行:并发执行的特例版, 10任务的内容都是一样的

<pre><code>

1. //串行队列, 线程同步,
   //1.获取串行队列
   //(1)获取系统创建好的串行队列,主队列,在主线程中执行
   // dispatch_queue_t queue = dispatch_get_main_queue();
   //(2)自己创建串行队列, 在子线程中执行
   dispatch_queue_t queue = dispatch_queue_create("frank", DISPATCH_QUEUE_SERIAL);
   //SERIAL串行
   //2.往队列中添加任务
   dispatch_async(queue, ^{
   NSLog(@"任务1,当前线程%@", [NSThread currentThread]);
   });
   dispatch_async(queue, ^{
   NSLog(@"任务2,当前线程%@", [NSThread currentThread]);
   });
   dispatch_async(queue, ^{
   NSLog(@"任务3,当前线程%@", [NSThread currentThread]);
   });
   dispatch_async(queue, ^{
   NSLog(@"任务4,当前线程%@", [NSThread currentThread]);
   });
2. //并行队列, 线程并发

• (IBAction)handleConcurrentQueue:(UIButton *)sender {
  //1.获取并行队列
  //(1)获取系统创建的并行队列
  dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
  //(2)自己创建并行队列
  // dispatch_queue_t queue = dispatch_queue_create("dd", DISPATCH_QUEUE_CONCURRENT);
  //2.往队列中添加任务
  dispatch_async(queue, ^{
  NSLog(@"任务1,当前线程%@", [NSThread currentThread]);
  });
  dispatch_async(queue, ^{
  NSLog(@"任务2,当前线程%@", [NSThread currentThread]);
  });
  dispatch_async(queue, ^{
  NSLog(@"任务3,当前线程%@", [NSThread currentThread]);
  });
  dispatch_async(queue, ^{
  NSLog(@"任务4,当前线程%@", [NSThread currentThread]);
  });
  //dispatch_sync 如果是添加的同步任务,任务同步执行全在主线程中处理,

}

//分组任务,

• (IBAction)handleGroup:(UIButton *)sender {
  //1.获取并发队列,
  dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
  //2.创建分组
  dispatch_group_t group = dispatch_group_create();
  //3.往队列中添加分组任务
  dispatch_group_async(group, queue, ^{
  NSLog(@"请求0~1M数据, 当前线程%@", [NSThread currentThread]);
  });
  dispatch_group_async(group, queue, ^{
  NSLog(@"请求1~2M数据, 当前线程%@", [NSThread currentThread]);
  });
  dispatch_group_async(group, queue, ^{
  NSLog(@"请求2~3M数据, 当前线程%@", [NSThread currentThread]);
  });
  dispatch_group_async(group, queue, ^{
  NSLog(@"请求3~4M数据, 当前线程%@", [NSThread currentThread]);
  });
  //所有分组任务完成之后触发
  dispatch_group_notify(group, queue, ^{
  //拼接分段数据
  NSLog(@"拼接分段数据, 当前线程为%@", [NSThread currentThread]);
  });
  }
  //整个应用程序运行期间,只执行一次
  //初始化方法和单例
• (IBAction)handleOnce:(UIButton *)sender {
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
  //存放只会执行一次的代码,比如单例对象的创建
  });
  }
  //障碍
• (IBAction)handleBarrier:(UIButton *)sender {
  //1.获取队列
  // dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
  //如果要加障碍任务,必须要使用自己创建的队列
  dispatch_queue_t queue = dispatch_queue_create("dd", DISPATCH_QUEUE_CONCURRENT);
  dispatch_async(queue, ^{
  NSLog(@"A 写入");
  });
  dispatch_async(queue, ^{
  NSLog(@"B 写入");
  });
  dispatch_async(queue, ^{
  NSLog(@"C 写入");
  });
  dispatch_barrier_async(queue, ^{
  NSLog(@"障碍, 读取数据");
  });
  dispatch_async(queue, ^{
  NSLog(@"D 写入");
  });
  dispatch_async(queue, ^{
  NSLog(@"E 写入");
  });
  dispatch_async(queue, ^{
  NSLog(@"F 写入");
  });

}
//延迟

• (IBAction)handleDelay:(UIButton *)sender {
  //1.
  double second = 2.0;
  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(second * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
  //存放延迟10秒之后执行的任务
  NSLog(@"Duck");
  });
  }
  //重复执行的任务
• (IBAction)handleApply:(UIButton *)sender {
  //并行队列
  // dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
  //串行队列
  dispatch_queue_t queue = dispatch_queue_create("cc", DISPATCH_QUEUE_SERIAL);
  NSArray *arr = @[@"aa", @"bb", @"cc", @"dd", @"ee", @"ff", @"gg", @"hh", @"ii", @"kk"];
  //如果每次只执行一个任务,则在主线程中执行,如果并发执行多个,在主线程之外,还会分配子线程
  dispatch_apply(arr.count, queue, ^(size_t index) {
  NSLog(@"任务%lu 当前线程%@", index + 1, [NSThread currentThread]);
  NSLog(@"%@", arr[index]);
  });

}

</code>