Question

我试过这个......

public ArrayList GetAllObjectAttributes()
    {
        List<Task> taskList = new List<Task>();
        ArrayList allObjectAttributes = new ArrayList();
        taskList.Add(Task.Factory.StartNew(() => { allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.Folder));}));
        taskList.Add(Task.Factory.StartNew(() => { allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.XMLFile)); }));
        taskList.Add(Task.Factory.StartNew(() => { allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.TextFile)); }));
        taskList.Add(Task.Factory.StartNew(() => { allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.Parent)); }));
        Task.WaitAll(taskList.ToArray());
        return allObjectAttributes;
    }

这......

public ArrayList GetAllObjectAttributes()
    {
        Thread[] threads = new Thread[4];
        ArrayList allObjectAttributes = new ArrayList();
        threads[0] = new Thread(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.Folder)));
        threads[1] = new Thread(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.XMLFile)));
        threads[2] = new Thread(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.TextFile)));
        threads[3] = new Thread(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.Parent)));

        foreach(Thread thread in threads)
        {
            thread.Start();
            thread.Join();
        }
        return allObjectAttributes;
    }

这也是......

public ArrayList GetAllObjectAttributes()
    {
        Thread[] threads = new Thread[4];
        ArrayList allObjectAttributes = new ArrayList();
        threads[0] = new Thread(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.Folder)));
        threads[1] = new Thread(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.XMLFile)));
        threads[2] = new Thread(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.TextFile)));
        threads[3] = new Thread(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.Parent)));

        foreach(Thread thread in threads)
        {
            thread.Start();
        }
        while(threads[0].IsAlive || threads[1].IsAlive || threads[2].IsAlive || threads[3].IsAlive)
        {
            Thread.Sleep(500);
        }
        return allObjectAttributes;
    }

我也试过了 Spawn Multiple Threads for work then wait until all finished

我仍然在allObjectAttributes中的一个arraylist项中得到一个null。

但是，当我这样做时

public ArrayList GetAllObjectAttributes()
    {
        ArrayList allObjectAttributes = new ArrayList();
        allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.Folder)));
        allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.XMLFile)));
        allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.TextFile)));
        allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.Parent)));
        return allObjectAttributes;
    }

我从未在arraylist项目中获得null项。

等到所有线程完成后我做错了什么？
任何其他建议，以便仅在所有4个线程完成执行后返回arraylist。

private List GetObjectAttributes(TreeViewAttrs tv)
{
    List objectAttributes = new List();
    string command = "COMMAND_TO_EXECUTE";
    if (command != "")
    {
        List results = RunCommand(command);
        if (results == null) { return null; }
        if (results.Count > 0)
        {
            foreach (string result in results)
            {
                if (!result.Contains("" + tv + ""))
                {
                    string[] res = reformatResponseString(result); //reformat the strings as per custom structure
                    if (res != null) { objectAttributes.Add(res); }
                }
            }
            return objectAttributes;
        }
    }
    return null;
}

Answer 1

使用线程安全集合（.NET 4.0兼容）略微改进：

List<Task> taskList = new List<Task>();
ConcurrentBag<object> allObjectAttributes = new ConcurrentBag<object>();

taskList.Add(Task.Factory.StartNew(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.Folder))));
taskList.Add(Task.Factory.StartNew(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.XMLFile))));
taskList.Add(Task.Factory.StartNew(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.TextFile))));
taskList.Add(Task.Factory.StartNew(() => allObjectAttributes.Add(GetObjectAttributes(TreeViewAttrs.Parent))));

Task.WaitAll(taskList.ToArray());

return allObjectAttributes;

替代方法：完成所有任务后使用Task.Result（不再需要线程安全集合，因为只有一个线程修改ArrayList）：

Task<object>[] taskList = {
    Task.Factory.StartNew(() => (object)GetObjectAttributes(TreeViewAttrs.Folder)),
    Task.Factory.StartNew(() => (object)GetObjectAttributes(TreeViewAttrs.XMLFile)),
    Task.Factory.StartNew(() => (object)GetObjectAttributes(TreeViewAttrs.TextFile)),
    Task.Factory.StartNew(() => (object)GetObjectAttributes(TreeViewAttrs.Parent))
};

Task.WaitAll(taskList);

ArrayList allObjectAttributes = new ArrayList();

foreach (Task<object> task in taskList) {
    allObjectAttributes.Add(task.Result);
}

return allObjectAttributes;

使用Task.WhenAll（仅限.NET 4.5）

显着改进：

object[] allObjectAttributes = await Task.WhenAll(
    Task.Run(() => GetObjectAttributes(TreeViewAttrs.Folder)),
    Task.Run(() => GetObjectAttributes(TreeViewAttrs.XMLFile)),
    Task.Run(() => GetObjectAttributes(TreeViewAttrs.TextFile)),
    Task.Run(() => GetObjectAttributes(TreeViewAttrs.Parent))
);

return allObjectAttributes;

*注意：我使用object作为通用参数，因为您保留了GetObjectAttributes未指定的返回类型。

Answer 2

您在第一个示例中使用的Task.WaitAll（）应该按预期工作。但是，我怀疑你所拥有的问题必须使用你使用的集合的线程安全性，ArrayList，而不是等待所有任务的完成这一事实。 ArrayList不提供线程安全性，因此您应该通过使用锁定机制或通过使用线程安全集合（例如ConcurrentBag（https://msdn.microsoft.com/en-us/library/dd381779(v=vs.110).aspx））来查看其他方法。

C＃等待所有线程完成执行

2 个答案: