我可以使用GCD限制并发请求吗?

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我正在从数据库异步获取数据.有什么方法可以将并发请求限制为一个数字，但仍然执行其余请求?

I'm acquiring data from a database asynchronously. Is there any way I can limit the concurrent requests to a number, but still execute the rest?

我看到了使用NSOperation和NSOperationQueue的帖子 但这对我来说太复杂了. 还有其他方法吗? GCD可以实现吗?

I saw a post using NSOperation and NSOperationQueue but this is too complicated for me. Is there any other ways to do it? Can GCD achieve it?

推荐答案

类似以下内容:

... //only make one of these obviously :) remaking it each time you dispatch_async wouldn't limit anything dispatch_semaphore_t concurrencyLimitingSemaphore = dispatch_semaphore_create(limit); ... //do this part once per task, for example in a loop dispatch_semaphore_wait(concurrencyLimitingSemaphore, DISPATCH_TIME_FOREVER); dispatch_async(someConcurrentQueue, ^{ /* work goes here */ dispatch_semaphore_signal(concurrencyLimitingSemaphore); }