C#Downloader：我应该使用Threads,BackgroundWorker还是ThreadPo

您可以通过使用带有信号量的队列来控制并发,或者,如果您使用的是.NET 4.0,则可以使用BlockingCollection.例如：

// Information used in callbacks.
class DownloadArgs
{
    public readonly string Url;
    public readonly string Filename;
    public readonly WebClient Client;
    public DownloadArgs(string u,string f,WebClient c)
    {
        Url = u;
        Filename = f;
        Client = c;
    }
}

const int MaxClients = 4;

// create a queue that allows the max items
BlockingCollection<WebClient> ClientQueue = new BlockingCollection<WebClient>(MaxClients);

// queue of urls to be downloaded (unbounded)
Queue<string> UrlQueue = new Queue<string>();

// create four WebClient instances and put them into the queue
for (int i = 0; i < MaxClients; ++i)
{
    var cli = new WebClient();
    cli.DownloadProgressChanged += DownloadProgressChanged;
    cli.DownloadFileCompleted += DownloadFileCompleted;
    ClientQueue.Add(cli);
}

// Fill the UrlQueue here

// Now go until the UrlQueue is empty
while (UrlQueue.Count > 0)
{
    WebClient cli = ClientQueue.Take(); // blocks if there is no client available
    string url = UrlQueue.Dequeue();
    string fname = CreateOutputFilename(url);  // or however you get the output file name
    cli.DownloadFileAsync(new Uri(url),fname,new DownloadArgs(url,cli));
}


void DownloadProgressChanged(object sender,DownloadProgressChangedEventArgs e)
{
    DownloadArgs args = (DownloadArgs)e.UserState;
    // Do status updates for this download
}

void DownloadFileCompleted(object sender,AsyncCompletedEventArgs e)
{
    DownloadArgs args = (DownloadArgs)e.UserState;
    // do whatever UI updates

    // now put this client back into the queue
    ClientQueue.Add(args.Client);
}

不需要显式管理线程或转到TPL.