任务 dispatch_async 与…

#define kBgQueue
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)

 

- (void)viewDidLoad

{

   
[super viewDidLoad];

 
  dispatch_async(kBgQueue,
^{

     
  NSData* data = [NSData dataWithContentsOfURL: kLatestKivaLoansURL];

   
    [self performSelectorOnMainThread:@selector(fetchedData:) withObject:datawaitUntilDone:YES];

    });

}

dispatch_async会向kBgQueue队列中添加新的任务去执行，这里kBgQueue队列使用dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)获得。

 

Dispatch Queues

Dispatch Queues从使用的角度将更象另一种形式的Operation Queues只是 Operation
Queuse是用ObjectC的Dispatch Queues是C的

dispatch Queues有serial Queues 也被称为私有dispatch
Queues，一个时间只能运行一个task，顺序运行

dispatch_queue_t queue;

queue = dispatch_queue_create("myQueue",
NULL);  

dispatch_async(queue, ^{

       
printf("Do some work here.\n");

    });

    printf("The
first block may or may not have run.\n");

   
dispatch_sync(queue, ^{

       
printf("Do some more work here.\n");

    });

    printf("Both
blocks have completed.\n");

这里使用了同步dispatch和异步dispatch，推荐使用dispatch_async这样才能真正体现其中的优势同步相当于WaitUntil
＝ YES

 

 

还有一种就是Concurrent Queues每个程序系统自动提供了3个Concurrent Queues

dispatch_queue_t aQueue =
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_queue_t aHQueue =
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);

 dispatch_queue_t aLQueue =
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);

啥意思一看就明白，3个优先级别的concurrent queues

 

最后一个特殊的Dispatch Queue就是main dispatch Queue 也是程序启动自动生成

dispatch_queue_t mainQueue = dispatch_get_main_queue();

 

concurrent queues和main queue 都是由系统生成而且 dispatch_suspend,
dispatch_resume, dispatch_set_context,这些函数对他们无效

 

但是我们的应用不是简单的同步也异步的运行，应用经常是混合的

比如我们要task1 task2 task3 都运行完成后才能异步运行task4 task5
task6我们该怎么做呢？这里我们可以引入group的概念

 

   
dispatch_queue_t aDQueue =
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
0);

   
dispatch_group_t group = dispatch_group_create();

    // Add a
task to the group

   
dispatch_group_async(group, aDQueue, ^{

       
printf("task 1 \n");

    });

   
dispatch_group_async(group, aDQueue, ^{

       
printf("task 2 \n");

    });

   
dispatch_group_async(group, aDQueue, ^{

       
printf("task 3 \n");

    });

    printf("wait
1 2 3 \n");

   
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);

    printf("task
1 2 3 finished \n");

   
dispatch_release(group);

    group =
dispatch_group_create();

    // Add a
task to the group

   
dispatch_group_async(gr
4000
oup, aDQueue, ^{

       
printf("task 4 \n");

    });

   
dispatch_group_async(group, aDQueue, ^{

       
printf("task 5 \n");

    });

   
dispatch_group_async(group, aDQueue, ^{

       
printf("task 6 \n");

    });

    printf("wait
4 5 6 \n");

   
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);

    printf("task
4 5 6 finished \n");

   
dispatch_release(group);

 

有时候我们也可以将设定一个数据在queue中 也可以定义一个结束函数

dispatch_set_finalizer_f 是在dispatch_release时候被调用

   
dispatch_queue_t serialQueue =
dispatch_queue_create("com.example.CriticalTaskQueue", NULL);

    if
(serialQueue)

    {

       
dispatch_set_context(serialQueue, self);

       
dispatch_set_finalizer_f(serialQueue,
&myFinalizerFunction);

    }

    

   
dispatch_group_t group = dispatch_group_create();

    

    // Add a
task to the group

   
dispatch_group_async(group, serialQueue, ^{

       
printf("task 1 \n");

    });

    

   
dispatch_group_async(group, serialQueue, ^{

       
printf("task 2 \n");

    });

    

   
dispatch_group_async(group, serialQueue, ^{

       
printf("task 3 \n");

    });

    printf("wait
1 2 3 \n");

   
dispatch_group_wait(group,
DISPATCH_TIME_FOREVER);  

   
dispatch_release(group);

   
dispatch_release(serialQueue);

- (void)checkUpdate
{
 
  dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_LOW, 0),
^{
     
  // Do a taks in the
background
 
   
  NSDictionary *dic = [iKnowAPI checkUpdate];

    
   
     
  // Hide the HUD in the
main tread 
     
  dispatch_async(dispatch_get_main_queue(),
^{
 
     
    if (dic &&
![[dic objectForKey:@"necessary"] isEqualToString:@"-1"]) 
 
     
    {
 
     
     
  NSString *message = [dic
objectForKey:@"des"];
 
     
     
  message = [message length] ? message :
NSLocalizedString(@"当前有新版本可以更新", @"");
 
     
     
  UIAlertView *alertView = [[UIAlertView alloc]
initWithTitle:NSLocalizedString(@"新版本提醒", @"")
 
     
     
     
     
     
     
     
     
     
     
   
  message:message 

    
     
     
     
     
     
     
     
     
     
     
  delegate:nil 
 
     
     
     
     
     
     
     
     
     
  cancelButtonTitle:NSLocalizedString(@"知道了", @"")
 
     
     
     
     
     
     
     
     
     
  otherButtonTitles:nil];

    
     
     
 
     
     
  [alertView show];
 
     
     
  [alertView release];
 
     
    }
 
      });
 
  });
}