[NET-501] Race Condition on TelnetClient.disconnect() and TelnetInputStream.run() . java.lang.IllegalStateException: Queue is full! Cannot process another character.

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.2
• Fix Version/s: 3.3
• Component/s: Telnet

Environment

Ubuntu 12.04 64 bits x86

• Assignee: Unassigned
• Reporter: Julián Lastiri
• Created: 07/Feb/13 22:07
• Updated: 12/Jun/13 21:09
• Resolved: 06/Jun/13 11:33

Description

I'm getting the following exception while disconnecting a threaded (readerThread=true) TelnetClient connection.

Exception in thread "Thread-160" java.lang.IllegalStateException: Queue is full! Cannot process another character. 
	at org.apache.commons.net.telnet.TelnetInputStream.__processChar(TelnetInputStream.java:339)
	at org.apache.commons.net.telnet.TelnetInputStream.run(TelnetInputStream.java:647)
	at java.lang.Thread.run(Thread.java:722)

I noticed that when TelnetClient.disconnect() is called the attribute _threaded is set to false while the thread in the TelnetInputStream.run() method could call TelnetInputStream()._processChar(...) throwing IllegalStateException

This is a test program to reproduce the issue

public class TestTelnetClient implements Runnable {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		ArrayList<Thread> workers = new ArrayList<Thread>();
		for( int i=0; i<1000; ++i){
			Thread t = new Thread ( new TestTelnetClient() );
			t.start();
			workers.add(t);
		}
		for (Thread t : workers ) {			
			try {
				t.join();			
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}			

	}

	@Override
	public void run() {
		System.out.println("Starting thread...");
		TelnetClient tc = new TelnetClient();
//		tc.setReaderThread(false);
		try {
			tc.connect("localhost", 23);
			tc.setSoTimeout(1000);
			InputStream in = tc.getInputStream();
			int ch;
			in.read();
		} catch (SocketException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			System.out.println("Disconnecting...");
			try {
				tc.disconnect();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		
	}

}

A telnet server (telnetd) is required. I also modified the initial banner ( /etc/issue.net ) with a lot of characters to get a better chance to receive information while calling disconnect.