async await 异步下载 异步代码加锁 lock 异步缓存

    async await 异步下载 异步代码加锁 lock 异步缓存

    FTP异步下载代码：

/// <summary>
/// 异步下载文件
/// </summary>
/// <param name="ftpPath">ftp路径</param>
/// <param name="ftpUserId">用户名</param>
/// <param name="ftpPassword">密码</param>
/// <param name="relativeFilePath">文件相对路径</param>
public static async Task<MemoryStream> DownloadFileAsync(string ftpPath, string ftpUserId, string ftpPassword, string relativeFilePath)
{
    FtpWebRequest request = null;

    try
    {
        LogTimeUtil log = new LogTimeUtil();
        request = (FtpWebRequest)WebRequest.Create(new Uri(Path.Combine(ftpPath, relativeFilePath).Replace("\\", "/")));
        request.Credentials = new NetworkCredential(ftpUserId, ftpPassword);
        request.Method = "RETR";
        FtpWebResponse response = (FtpWebResponse)(await request.GetResponseAsync());
        Stream responseStream = response.GetResponseStream();
        MemoryStream stream = new MemoryStream();
        byte[] bArr = new byte[1024 * 1024];
        int size = await responseStream.ReadAsync(bArr, 0, (int)bArr.Length);
        while (size > 0)
        {
            stream.Write(bArr, 0, size);
            size = await responseStream.ReadAsync(bArr, 0, (int)bArr.Length);
        }
        stream.Seek(0, SeekOrigin.Begin);
        responseStream.Close();

        log.LogTime("FtpUtil.DownloadFileAsync 下载 filePath=" + relativeFilePath);
        return stream;
    }
    catch (Exception ex)
    {
        request.Abort();
        LogUtil.Error(ex);
    }

    return null;
}

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