C# 等待所有线程完成执行

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;
    }

还有这个……

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;
    }

还有这个……

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 Spawn Multiple Threads for work then wait until all finished

我仍然在 allObjectAttributes 中的一个数组列表项中得到一个 null。

但是，当我这样做的时候

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;
    }

我从来没有在 arraylist 项目中得到一个 null 项目。

1. 等待所有线程完成我做错了什么？
2. 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

通过使用线程安全集合(.NET 4.0 兼容)略有改进:

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;

另一种方法:在所有任务完成后使用 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;

显着通过使用 Task.WhenAll 改进(仅限 .NET 4.5):

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，因为您未指定 GetObjectAttributes 的返回类型。