ios - 序列化异步方法

Question

我有许多需要串行执行的任务，但任务包括完成块中的下一个块。

什么是一次完成这些任务的好技术，在当前任务完成其完成块后开始下一个任务？

除了具有串行 NSOperationQueue 的 NSOperation 子类之外，还有其他技术吗？

Answer 1

标准解决方案：

1. NSOperationQueue与. maxConcurrentOperationCount_ 1你说你不想那样做，但你没有说为什么。串行队列是最合乎逻辑的解决方案。

   例如：

   NSOperationQueue *queue = [[NSOperationQueue alloc] init];
   queue.maxConcurrentOperationCount = 1;
   
   [queue addOperationWithBlock:^{
       NSLog(@"Starting #1");
       sleep(3);
       NSLog(@"Finishing #1");
   }];
   
   [queue addOperationWithBlock:^{
       NSLog(@"Starting #2");
       sleep(3);
       NSLog(@"Finishing #2");
   }];
   
   [queue addOperationWithBlock:^{
       NSLog(@"Starting #3");
       sleep(3);
       NSLog(@"Finishing #3");
   }];
   

2. 如果您不想要 serial NSOperationQueue，您可以使用标准并发队列，但只需使每个操作都依赖于前一个操作。您将在不使用串行队列的情况下实现您正在寻找的串行行为。

   例如：

   NSOperationQueue *queue = [[NSOperationQueue alloc] init];
   
   NSOperation *operation;
   NSOperation *previousOperation;
   
   operation = [NSBlockOperation blockOperationWithBlock:^{
       NSLog(@"Starting #1");
       sleep(3);
       NSLog(@"Finishing #1");
   }];
   [queue addOperation:operation];
   
   previousOperation = operation;
   operation = [NSBlockOperation blockOperationWithBlock:^{
       NSLog(@"Starting #2");
       sleep(3);
       NSLog(@"Finishing #2");
   }];
   [operation addDependency:previousOperation];
   [queue addOperation:operation];
   
   previousOperation = operation;
   operation = [NSBlockOperation blockOperationWithBlock:^{
       NSLog(@"Starting #3");
       sleep(3);
       NSLog(@"Finishing #3");
   }];
   [operation addDependency:previousOperation];
   [queue addOperation:operation];
   

3. 您还可以使用dispatch_queue_create. 除了使用 GCD 而不是NSOperationQueue.

   例如：

   dispatch_queue_t queue = dispatch_queue_create("com.ConnerDouglass.operationtest", 0);
   
   dispatch_async(queue, ^{
       NSLog(@"Starting #1");
       sleep(3);
       NSLog(@"Finishing #1");
   });
   
   dispatch_async(queue, ^{
       NSLog(@"Starting #2");
       sleep(3);
       NSLog(@"Finishing #2");
   });
   
   dispatch_async(queue, ^{
       NSLog(@"Starting #3");
       sleep(3);
       NSLog(@"Finishing #3");
   });
   

Answer 2

我认为这是一个有趣的解决方案：https ://github.com/berzniz/Sequencer

Answer 3

像这样的东西怎么样：

-(void)start
{
    // Start the async chain
    [self performSelectorInBackground:@selector(action1) withObject:nil];
}
-(void)notifyDone:(NSNumber *)taskID
{
    NSLog(@"Done with task #%i", taskID.intValue);
}
-(void)action1
{
    // Do some fancy async stuff here
    // Now, we are done. Notify the main thread that task 1 is complete.
    [self performSelectorOnMainThread:@selector(nofityDone:) withObject:[NSNumber numberWithInt:1] waitUntilDone:YES];
    // Move onto the next task once the main thread is done handling the notification
    [self action2];
}
-(void)action2
{
    // Do the same sort of thing as "action1" did, then call he next method
}