WebClient DownloadData 的高内存使用率

Question

在 webclient 下载数据后，我有一个问题内存没有被释放，所以我用下面的示例代码进行了测试，它也发生了。 GC 最多收集了 10-20%，但仍然留下太多，我真的不知道可能出了什么问题，因为似乎没有其他人有问题。

---

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        list.Add("https://media1.giphy.com/media/Uwj2CxFJs8ZyM/giphy.gif");
        list.Add("https://media0.giphy.com/media/5Ut5IWqO2kfDU1FG8T/giphy.gif");
        list.Add("https://media1.giphy.com/media/Uwj2CxFJs8ZyM/giphy.gif");
        list.Add("https://media0.giphy.com/media/5Ut5IWqO2kfDU1FG8T/giphy.gif");
        list.Add("https://media1.giphy.com/media/Uwj2CxFJs8ZyM/giphy.gif");
        list.Add("https://media0.giphy.com/media/5Ut5IWqO2kfDU1FG8T/giphy.gif");
        list.Add("https://media1.giphy.com/media/Uwj2CxFJs8ZyM/giphy.gif");
        list.Add("https://media0.giphy.com/media/5Ut5IWqO2kfDU1FG8T/giphy.gif");
        list.Add("https://media1.giphy.com/media/Uwj2CxFJs8ZyM/giphy.gif");
        list.Add("https://media0.giphy.com/media/5Ut5IWqO2kfDU1FG8T/giphy.gif");
    }

    private List<string> list = new List<string>();
    public void DownloadThumb(string Url)
    {
        WebClient ThumbClient = new WebClient();
        ThumbClient.DownloadDataCompleted += DownloadFinished;
        ThumbClient.DownloadDataAsync(new Uri(Url));
    }

    private int donecount = 0;
    public void DownloadFinished(object sender, DownloadDataCompletedEventArgs e)
    {
        Image DownloadedImage;
        using (MemoryStream MemoryStreamTemp = new MemoryStream(e.Result))
        {
            DownloadedImage = Image.FromStream(MemoryStreamTemp);
        }
        DownloadedImage.Dispose();
        ((WebClient)sender).Dispose();

        donecount++;
        if (donecount == list.Count)
        {
            donecount = 0;
            button1.Enabled = true;
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {
        button1.Enabled = false;
        foreach (string TempString in list)
        {
            DownloadThumb(TempString);
        }
    }

    private void button2_Click(object sender, EventArgs e)
    {
        GC.Collect();
    }
}

Answer 1

答案是更改为 HttpClient，因为 WebClient 不应该那样使用，而且它也较旧并且基本上已经过时。

使用以下代码，内存使用量在开始时为 60MB > 下载后为 600 > GC 后为 200 > 在大约 90 秒后 GC 时为 70。

---

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        list.Add("https://media1.giphy.com/media/Uwj2CxFJs8ZyM/giphy.gif");
        list.Add("https://media0.giphy.com/media/5Ut5IWqO2kfDU1FG8T/giphy.gif");
        list.Add("https://media1.giphy.com/media/Uwj2CxFJs8ZyM/giphy.gif");
        list.Add("https://media0.giphy.com/media/5Ut5IWqO2kfDU1FG8T/giphy.gif");
        list.Add("https://media1.giphy.com/media/Uwj2CxFJs8ZyM/giphy.gif");
        list.Add("https://media0.giphy.com/media/5Ut5IWqO2kfDU1FG8T/giphy.gif");
        list.Add("https://media1.giphy.com/media/Uwj2CxFJs8ZyM/giphy.gif");
        list.Add("https://media0.giphy.com/media/5Ut5IWqO2kfDU1FG8T/giphy.gif");
        list.Add("https://media1.giphy.com/media/Uwj2CxFJs8ZyM/giphy.gif");
        list.Add("https://media0.giphy.com/media/5Ut5IWqO2kfDU1FG8T/giphy.gif");
    }

    //Becase https://qa.ostack.cn/qa/?qa=619128
    static HttpClientHandler handler = new HttpClientHandler();

    private List<string> list = new List<string>();
    static readonly HttpClient ThumbClient = new HttpClient(handler);
    public async Task<Image> DownloadThumb(string Url)
    {
        byte[] bytes = await ThumbClient.GetByteArrayAsync(new Uri(Url));
        Image DownloadedImage = (Image)new ImageConverter().ConvertFrom(bytes);
        return DownloadedImage;
    }

    private async void button1_Click(object sender, EventArgs e)
    {
        button1.Enabled = false;
        List<Task<Image>> tasks = new List<Task<Image>>();
        list.ForEach(s => tasks.Add(DownloadThumb(s)));
        await Task.WhenAll(tasks);
        foreach (Task<Image> task in tasks)
        {
            task.Dispose();
        }
        button1.Enabled = true;
    }

    private void button2_Click(object sender, EventArgs e)
    {
        GC.WaitForPendingFinalizers();
        GC.Collect();
    }
}