切换到root帐户并执行cd / root

Question

下面是代码预览

import os.log

var value = 10
let lock = NSLock()   // a lock to synchronize our access to `value`

func notifyExperiment() {
    // rather than using `DispatchWorkItem`, a reference type, and invoking it multiple times,
    // let's just define some closure or function to run some task

    func performTask(message: String) {
        os_log("starting %@", message)
        Thread.sleep(forTimeInterval: 2)    // we wouldn't do this in production app, but lets do it here for pedagogic purposes, slowing it down enough so we can see what's going on
        lock.lock()
        value += 5
        lock.unlock()
        os_log("done %@", message)
    }

    // create a dispatch group to keep track of when these tasks are done

    let group = DispatchGroup()

    // let's enter the group so that we don't have race condition between dispatching tasks
    // to the queues and our notify process

    group.enter()

    // define what notification will be done when the task is done

    group.notify(queue: .main) {
        self.lock.lock()
        os_log("value = %d", self.value)
        self.lock.unlock()
    }

    // Let's run our task once on the global queue

    DispatchQueue.global(qos: .utility).async(group: group) {
        performTask(message: "from global queue")
    }

    // Let's run our task also on a custom queue

    let customQueue = DispatchQueue(label: "com.appcoda.delayqueue1", qos: .utility)
    customQueue.async(group: group) {
        performTask(message: "from custom queue")
    }

    // Now let's leave the group, resolving our `enter` at the top, allowing the `notify` block
    // to run iff (a) all `enter` calls are balanced with `leave` calls; and (b) once the `async(group:)`
    // calls are done.

    group.leave()
}

当我运行此脚本时。它挂了。我认为它不会切换到root并执行其余的行。

有人可以帮助我让它发挥作用。