[NET-685] FTPClient.connect() hangs without any timeout and response. It blocks the whole JVM

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.6
• Fix Version/s: 3.8.0
• Component/s: FTP

Environment

OS: Debian 9

Java Version: 1.8

Scheduler: On made development using Spring-boot. Multithreading Environment using Runnable Class.

 

• Flags: Important
• Assignee: Unassigned
• Reporter: Simone
• Created: 29/Jun/20 09:52
• Updated: 29/Nov/20 19:52
• Resolved: 29/Nov/20 19:52

Description

Hello Everybody,

we implemented a multithread scheduler in order to run many FTP connections (one for each customer). We use these connections to upload /download files from/to remote servers.

Inside the scheduler, we use a ScheduledThreadPoolExecutor to run our FTP connections (about 50). We run one thread (which instantiates an FTPClient object) for each FTP connection.

Sometimes, one of those connections tries to connect to the FTP server and the method FTPClient.connect() hangs without any timeout. No log. No server response.
The connection is blocked as well as the whole JVM. 

We needed to restart the service to fix the production.

We already checked the following points during the issue:

• the server is reachable;
• No overlapping between run threads;
• the virtual machine runs correctly;
• Every other connection works correctly (FTPS, SFTP, CIFS, ...) so far.

(Production logs attached)

PULL-REQUEST link: https://github.com/apache/commons-net/pull/51

Thanks in advance,
Simone

Issue Links

• links to: GitHub Pull Request #51