使用FluentFTP从FTP同时下载多个文件，最大值 [英] Download multiple files concurrently from FTP using FluentFTP with a maximum value

问题描述

我想从FTP目录中递归下载多个下载文件，为此，我正在使用FluentFTP库，而我的代码是这样的:

I would like to download multiple download files recursively from a FTP Directory, to do this I'm using FluentFTP library and my code is this one:

private async Task downloadRecursively(string src, string dest, FtpClient ftp)
{

    foreach(var item in ftp.GetListing(src))
    {
        if (item.Type == FtpFileSystemObjectType.Directory)
        {
            if (item.Size != 0)
            {
                System.IO.Directory.CreateDirectory(Path.Combine(dest, item.Name));
                downloadRecursively(Path.Combine(src, item.Name), Path.Combine(dest, item.Name), ftp);
            }
        }
        else if (item.Type == FtpFileSystemObjectType.File)
        {
            await ftp.DownloadFileAsync(Path.Combine(dest, item.Name), Path.Combine(src, item.Name));
        }
    }
}

我知道您每次下载都需要一个FtpClient，但是我该如何最大程度地使用一定数量的连接，我想这个想法是针对我找到的每个文件创建，连接，下载和关闭.同时具有X个下载文件.另外，我不确定是否应该使用异步，线程和我最大的问题(如何实现所有这些功能)创建Task.

I know you need one FtpClient per download you want, but how can I make to use a certain number of connections as maximum, I guess that the idea is to create, connect, download and close per every file I find but just having a X number of downloading files at the same time. Also I'm not sure if I should create Task with async, Threads and my biggest problem, how to implement all of this.

来自 @Bradley 的答案似乎不错，但问题是确实读取了必须从外部下载的每个文件文件，并且没有最大的并发下载值，因此我不确定如何应用这两个要求.

Answer from @Bradley here seems pretty good, but the question does read every file thas has to download from an external file and it doesn't have a maximum concurrent download value so I'm not sure how to apply these both requirements.

推荐答案

使用:

• ConcurrentBag 类以实现连接池；
• Parallel 类使操作并行化；
• ParallelOptions.MaxDegreeOfParallelism 限制并发线程数.

var clients = new ConcurrentBag<FtpClient>();

var opts = new ParallelOptions { MaxDegreeOfParallelism = maxConnections };
Parallel.ForEach(files, opts, file =>
{
    file = Path.GetFileName(file);

    string thread = $"Thread {Thread.CurrentThread.ManagedThreadId}";
    if (!clients.TryTake(out var client))
    {
        Console.WriteLine($"{thread} Opening connection...");
        client = new FtpClient(host, user, pass);
        client.Connect();
        Console.WriteLine($"{thread} Opened connection {client.GetHashCode()}.");
    }

    string remotePath = sourcePath + "/" + file;
    string localPath = Path.Combine(destPath, file);
    string desc =
        $"{thread}, Connection {client.GetHashCode()}, " +
        $"File {remotePath} => {localPath}";
    Console.WriteLine($"{desc} - Starting...");
    client.DownloadFile(localPath, remotePath);
    Console.WriteLine($"{desc} - Done.");

    clients.Add(client);
});

Console.WriteLine($"Closing {clients.Count} connections");
foreach (var client in clients)
{
    Console.WriteLine($"Closing connection {client.GetHashCode()}");
    client.Dispose();
}

---

另一种方法是启动固定数量的线程，每个线程具有一个连接，并让它们从队列中选择文件.

---

Another approach is to start a fixed number of threads with one connection for each and have them pick files from a queue.

有关实现的示例，请参阅我关于WinSCP .NET程序集的文章:
通过SFTP/FTP协议自动并行连接中的传输

For an example of an implementation, see my article for WinSCP .NET assembly:
Automating transfers in parallel connections over SFTP/FTP protocol

关于SFTP的类似问题:
使用C#Parallel.ForEach循环处理SFTP文件而不处理下载

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