For every build, SSH Client plugin create a thread that never ends.
It seems to come from this class :
com/cloudbees/jenkins/plugins/sshagent/jna/AgentServer.java

thread = new Thread() {
    public void run() {
        try {
            while (!stopped) {
                final UnixSocketChannel clientSock = channel.accept();
                clientSock.configureBlocking(true);
                new SshAgentSession(clientSock, agent);
            }
        } catch (Exception e) {
            if (!stopped) {
                e.printStackTrace();
            }
        }
    }
};

I do not really understand the while loop necessity here. The thread will hang in the "channel.accept()" method only the second time it passes in.

Here is the stack :

"Thread-2000" prio=10 tid=0x0000000040e2f800 nid=0x527e runnable [0x00007ff5ec313000]
java.lang.Thread.State: RUNNABLE
at com.kenai.jffi.Foreign.invokeN3O2(Native Method)
at com.kenai.jffi.Invoker.invokeN3(Invoker.java:1092)
at jnr.unixsocket.Native$LibC$jnr$ffi$0.accept(Unknown Source)
at jnr.unixsocket.Native.accept(Native.java:91)
at jnr.unixsocket.UnixServerSocketChannel.accept(UnixServerSocketChannel.java:56)
at com.cloudbees.jenkins.plugins.sshagent.jna.AgentServer$1.run(AgentServer.java:77)