序列化异步方法

问题描述

我有许多任务需要串行执行，但是该任务包括完成块中的下一个块.

I have a number of tasks I need to execute serially but the task includes next block in a completion block.

什么是一次完成一次任务，在当前任务完成其完成任务之后又开始下一个任务的好的技术?

What is a good technique for doing these tasks one at a time, starting the next task after the current one completes its completion block?

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

Is there a technique other than a NSOperation subclass with a serial NSOperationQueue?

推荐答案

标准解决方案:

1. NSOperationQueue，其中maxConcurrentOperationCount为1.您说您不想这样做，但您不说原因.串行队列是最合乎逻辑的解决方案.

1. NSOperationQueue with maxConcurrentOperationCount of 1. You say you don't want to do that, but you don't say why. Serial queues are the most logical solution.

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");
}];

如果您不想使用串行NSOperationQueue，则可以使用标准并发队列，而只需使每个操作都依赖于前一个即可.您无需使用串行队列即可实现所需的串行行为.

If you don't want a serial NSOperationQueue, you can use a standard concurrent queue, but just make each operation dependent upon the prior one. You'll achieve the serial behavior you're looking for without using a serial queue.

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];

您还可以使用dispatch_queue_create创建GCD串行队列.除了使用GCD代替NSOperationQueue.

You could also create a GCD serial queue with dispatch_queue_create. It achieves the same thing as the first option, except using GCD instead of 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");
});

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