Question

我遇到了一些CoreData并发问题。当目标线程被context.perform阻止时，我无法DispatchGroup。

以下是一个显示问题的简单示例：

func upload(objects: [NSManagedObject]) {
    let group = DispatchGroup()
    for object in objects {
        group.enter()
        upload(object) {
            group.leave()
        }
    }
    group.wait()    // current thread is blocked here

    someAdditionalWorkToDoInSameThread()
}

func upload(object: NSManagedObject, completion: ()->()) {
    let context = object.managedObjectContext
    performAlamofireRequest(object) {
        context.perform {
            // can't reach here because the thread is blocked
            update(object)
            completion()
        }
    }
}

请帮助我重新实现这一点。感谢。

Answer 1

在调度组上使用notify而不是等待，应解决您的问题。

调用wait()阻止当前线程完成以前提交的工作。
notify(queue:execute:)将通知您传递的队列作为组任务已完成的参数。

func upload(objects: [NSManagedObject], completion: ()->()) {
    let group = DispatchGroup()
    for object in objects {
        group.enter()
        upload(object) {
            group.leave()
        }
    }
    group.notify(queue: DispatchQueue.main) {
         completion()
    }
}

Swift：使用DispatchGroup进行死锁

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