Question

我需要执行许多串行执行的任务，但任务包括完成块中的下一个块。

一次执行这些任务的好方法是什么，在当前完成其完成块之后开始下一个任务？

是否有一种非NSOperation子类的技术与序列NSOperationQueue？

Answer 1

标准解决方案：

NSOperationQueue maxConcurrentOperationCount 1。你说你不想这样做，但你不说为什么。串行队列是最合理的解决方案。

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");
}];

如果您不需要序列NSOperationQueue，则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];

您还可以使用dispatch_queue_create创建GCD序列队列。它实现了与第一个选项相同的功能，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

这样的事情：

-(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
}

序列化异步方法

3 个答案: