c# - 当其中一个下载线程终止时解锁 FIleStream

Question

我通过例如下载文件5 个线程。当其中一个线程完成下载文件部分时 - 它被中止，但所有其余线程都有 ThreadState = WaitSleepJoin 并且显然停止下载。如何解决？

while ((bytesSize = responseStream.Read(Buffer, 0, Buffer.Length)) > 0)
{
    lock(fileStream)
    {
        fileStream.Write(Buffer, 0, bytesSize);

        if (DownloadedBytesCount >= EndPosition - StartPosition)
        {
            downThread.Abort();
            break;
        }
        else DownloadedBytesCount += bytesSize;
    }               
}

我想 fileStream 在 downThread.Abort() 之后仍然被阻塞。我以为中断会解锁文件流，但事实并非如此。那么如何解锁该文件呢？

这里有更多信息:

我有一个类“ThreadFileManager”:

public class ThreadFileManager
{
    public ThreadContent[] threads;
    protected static FileStream fileStream { get; set; }

    public ThreadFileManager(string fileUrl, string LocalPath, int ThreadCount, int bufferLength, ProgressBar progressBarReference)
    {
        if (File.Exists(LocalPath))
            fileStream = new FileStream(LocalPath, FileMode.Append, FileAccess.Write);
        else fileStream = new FileStream(LocalPath, FileMode.Create, FileAccess.Write);

        CreateThreads(fileUrl, ThreadCount, bufferLength); //create threads and start downloading
    }

    private void CreateThreads(string fileUrl, int ThreadCount, int bufferLength)
    {
        webRequest = (HttpWebRequest)WebRequest.Create(fileUrl);

        webRequest.Credentials = CredentialCache.DefaultCredentials;

        webResponse = (HttpWebResponse)webRequest.GetResponse();
        responseStream = webResponse.GetResponseStream();

        //calculate the total bytes count to download per one thread
        long part = webResponse.ContentLength / ThreadCount;
        fileLength = webResponse.ContentLength;

        this.threads = new ThreadContent[ThreadCount];

        ThreadContent thr_cn = new ThreadContent(bufferLength, fileUrl);
        thr_cn.StartPosition = 0;
        thr_cn.EndPosition = part;

        threads[0] = thr_cn;

        for (int i = 1; i < ThreadCount; i++)
        {
            thr_cn = new ThreadContent(bufferLength, fileUrl);

            thr_cn.StartPosition = (i * part) + 1;
            thr_cn.EndPosition = (i + 1) * part;
            this.threads[i] = thr_cn;
        }
    }
}

public class ThreadContent : ThreadFileManager
{
    public long StartPosition { get; set; } //the Begining position of the downloading file
    public long EndPosition { get; set; } //the End position of the downloading file
    public byte[] Buffer { get; set; }

    HttpWebRequest webRequest { get; set; }
    HttpWebResponse webResponse { get; set; }
    long BufferLength { get; set; }
    long DownloadedBytesCount { get; set; }

    Thread downThread;
    string FileURL { get; set; }

    public ThreadContent(int bufferLength, string url)
    {
        Buffer = new byte[bufferLength];
        downThread = new Thread(new ThreadStart(Download));
        FileURL = url;
    }

    public void Download()
    {
        int bytesSize = 0;
        webRequest = (HttpWebRequest)WebRequest.Create(FileURL);

        webRequest.Credentials = CredentialCache.DefaultCredentials;

        webResponse = (HttpWebResponse)webRequest.GetResponse();
        responseStream = webResponse.GetResponseStream();

        webRequest.AddRange(StartPosition, EndPosition);

        while ((bytesSize = responseStream.Read(Buffer, 0, Buffer.Length)) > 0)
        {
            lock (fileStream)
            {
                fileStream.Write(Buffer, 0, bytesSize);
                base.UpdateProgress(bytesSize);
            }

            if (DownloadedBytesCount >= EndPosition - StartPosition)
            {
                downThread.Abort();
                break;
            }
            else DownloadedBytesCount += bytesSize;
        }
    }

Answer 1

一般来说，您的方法是不正确的，因为您不应该通过调用 Abort() 来结束您的线程。这最终会引发异常。我尝试的方法是只允许线程返回而不是中止。您可以通过传递关于何时返回的线程信息来做到这一点。另一种方法(可能更好)是使用 AutoResetEvent，并在您希望每个线程结束时使用 Set()。线程内部的代码应该是这样的:

AutoResetEvent e = new AutoResetEvent( false);
while( !e.WaitOne( 0)) {
  // your code here
}

您似乎希望这 5 个线程共享有关下载状态的信息，即每个线程已下载了多少字节。如果你想要实时更新(我假设)，你可以将对计数的引用传递给每个线程，并确保每个线程使用锁来保护对该变量的访问。或者你可以让它每 1K 或更多更新一次字节数，这样你就不会锁定和解锁一堆。

如果你有一个管理这些多个下载线程的工作线程，那么你可以启动每个线程，然后从“主”工作线程(即不是主线程本身，否则你的 GUI 将阻塞)使用 EndInvoke 来确保每个线程已经正常结束。或者您可以使用 AsyncCallback，它会在每个线程完成时被调用。在 AsyncCallback 中，您可以调用 EndInvoke。