Kotlin / anko多个异步任务

Fire095 发表于 Dev

火095

我正在寻找一种并行启动多个任务并等待所有任务完成的简单方法。

考虑下面的C＃示例：

private static void Main(string[] args)
{
    var urlList = new[] {"http://www.microsoft.com/", "http://www.google.com/", "http://www.apple.com/" };
    var result = GetHtml(urlList);
}

private static List<string> GetHtml(string[] urlList)
{
    var tasks = new List<Task>();
    var output = new List<string>();

    foreach (var url in urlList)
    {
        var task = new Task(() =>
        {
            var html = new WebClient().DownloadString(url);
            output.Add(html);
        });

        tasks.Add(task);

        //starts task in a separate thread (doesn't block anything)
        task.Start();
    }

    //waits for all tasks (running in parallel) to complete before exiting method
    Task.WaitAll(tasks.ToArray());

    return output;
}

GetHtml方法并行下载多个网页并返回html字符串列表。

如何使用kotlin / anko实现此目的？

private fun GetHtml(urlList: Array<String>): ArrayList<String> {

    val tasks = ArrayList<Future<Unit>>()
    val output = ArrayList<String>()

    for (url in urlList) {
        val task = async() {
            //some java-code that downloads html from <url>, doesn't matter for now
            output.add("html for $url")
        }
        tasks.add(task)
    }

    //this is NOT parallel execution
    for (task in tasks) {
        task.get()           
    }

    //tasks.getall() ?? 

    return output
}

火095

根据Michael和pdegand59的输入，这是一个可行的解决方案：

private fun GetHtml(urlList: Array<String>): ArrayList<String> {

    val pool = Executors.newFixedThreadPool(urlList.count())
    val countDownLatch = CountDownLatch(urlList.count())

    val output = ArrayList<String>()

    for (url in urlList) {  

        async(pool, {
            //some java-code that downloads html for <url>
            output.add("html for $url")
            countDownLatch.countDown()
        })      
    }

    countDownLatch.await()

    return output
}