如何监控递归调度队列的任务何时全部完成?

与调度组.通知直到最后一刻才打来调度组请假是叫,所以你叫 enter 外部 leave 里面

比如:

func findPath(node: Node) {
  if !node.isValid { return }
  dispatchGroup.enter()
  queue.async { //concurrent queue
    findPath(node.north)
    dispatchGroup.leave()
  }

  dispatchGroup.enter()
  queue.async {
    findPath(node.west)
    dispatchGroup.leave()
  }

  dispatchGroup.enter()
  queue.async {
    findPath(node.south)
    dispatchGroup.leave()
  }

  dispatchGroup.enter()
  queue.async {
    findPath(node.east)
    dispatchGroup.leave()
  }
}


func findPaths(startNode: Node) {
    findPath(node: startNode)
    dispatchGroup.notify {
        print("All done")
    }
}