C#等待所有线程完成执行

发布时间：2020-12-15 23:29:06 所属栏目：百科来源：网络整理

导读：我试过这个…… public ArrayList GetAllObjectAttributes() { ListTask taskList = new ListTask(); ArrayList allObjectAttributes = new ArrayList(); taskList.Add(Task.Factory.StartNew(() = { allObjectAttributes.Add(GetObjectAttributes(TreeViewA

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;
    }

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,以便只有在所有4个线程完成执行后才返回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;
}

解决方法

使用线程安全集合(.NET 4.0兼容)稍微改进：

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了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：我使用了对象作为通用参数,因为你保留了未指定的GetObjectAttributes的返回类型.

（编辑：李大同）

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