是否有必要在多线程Paramiko中为每个线程打开一个SFTPClient? [英] Is it necessary to open a SFTPClient per one thread in Paramiko with multi-threading?

问题描述

我想使用 Paramiko 和多线程从远程服务器下载文件.

I want to download files from remote server using Paramiko with multithreading.

我想到了两个解决方案，但我不确定哪个是正确的(或更好).

There are two solution came into my mind, but I'm not sure which is right (or better).

解决方案 1:假设 SFTPClient.get 是线程安全的(但我找不到任何提到的文档)，一个简单的:

Solution 1: Assuming that the SFTPClient.get is thread safe (But I can't find any document mentioned that), a simple one would as:

from paramiko import SSHClient, AutoAddPolicy, SFTPClient
from concurrent.futures import ThreadPoolExecutor
from typing import List

client = SSHClient()
ciient.set_missing_host_key_policy(AutoAddPolicy())
client.connect( ... )
sftp = client.open_sftp()

files_to_download: List[str] = ...

with ThreadPoolExecutor(10) as pool:
    pool.map(lambda fn: sftp.get(fn, fn), files_to_download)

解决方案 2:解决方案 1

1. Paramiko 的 API 真的是线程安全的吗?
2. 通过单个连接下载多个文件是否有效?

这是我的第二个解决方案:

So here is my second solution:

from paramiko import SSHClient, AutoAddPolicy, SFTPClient
from concurrent.futures import ThreadPoolExecutor
from threading import Lock, local
from typing import List

client = SSHClient()
ciient.set_missing_host_key_policy(AutoAddPolicy())
client.connect( ... )
thread_local = local()
thread_lock  = Lock()

files_to_download: List[str] = ...

def download(fn: str) -> None:
    """
    thread-safe and each thread has its own SFTPClient
    """
    if not hasattr(thread_local, 'sftp'):
        with thread_lock:
            thread_local.sftp = client.open_sftp()
    thread_local.sftp.get(fn, fn)

with ThreadPoolExecutor(10) as pool:
    pool.map(download, files_to_download)

哪种解决方案更好?

推荐答案

Paramiko 不是线程安全的.

Paramiko is not thread safe.

在一个连接上使用多个线程可能无论如何都无法提供您希望的性能.您必须为每个线程打开一个单独的连接 (SSHClient/SFTPClient).

Using multiple threads over one connection might not give you the performance you hope for anyway. You would have to open a separate connection (SSHClient/SFTPClient) per thread.

只有在传输大量小文件之类的情况下，才能通过一个连接获得更好的性能.为此，请参阅使用 SFTP 缓慢上传许多小文件.

With one connection, you would have better performance, only with scenarios like a transfer of large amount of small files. For that, see Slow upload of many small files with SFTP.

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