Session.connect() hangs without any timeout and response. It blocks the whole JVM

Hello Everybody,

we implemented a multithread scheduler in order to run many SFTP 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 SFTP connections (about 50). We run one thread (which instantiates an JSch object and Session object) for each SFTP connection.

Sometimes, one of those connections tries to connect to the SFTP server and the method session.connect() hangs without any timeout. No logs. 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, FTP, CIFS, ...) so far.

Thanks in advance,
Simone