ThreadDeath problem

Here is my current best guess.

Note that Beaming's stacktrace includes:

<pre>
...
at net.sf.robocode.host.proxies.BasicRobotProxy.forceStopThread(BasicRobotProxy.java:44)
at net.sf.robocode.battle.peer.RobotPeer.checkSkippedTurn(RobotPeer.java:649)
...
</pre>

Therefore, <code>RobotPeer.checkSkippedTurn()</code> called <code>BasicRobotProxy.forceStopThread()</code>

The source code of [https://github.com/robo-code/robocode/blob/0eb93ba532bc6731b7ff8dd02da1308d92ccb2fd/robocode.battle/src/main/java/net/sf/robocode/battle/peer/RobotPeer.java#L626 <code>RobotPeer.checkSkippedTurn()</code>] shows '''one and only one''' possible call to <code>BasicRobotProxy.forceStopThread()</code>:

<syntaxhighlight lang="java">
public void checkSkippedTurn() {
    // ...
    if (/* snip */) {
        println("SYSTEM: " + getShortName() + " has not performed any actions in a reasonable amount of time.");
        println("SYSTEM: No score will be generated.");
        /* snip */
        robotProxy.forceStopThread();
    }
}
</syntaxhighlight>

Therefore, control flow must have passed through this path.

Note that this code sequence includes a <code>println("SYSTEM: <Bot> has not performed any actions...")</code> call, which must have been executed, yet no such SYSTEM message is present in Beaming's log.

The source code of the [https://github.com/robo-code/robocode/blob/0eb93ba532bc6731b7ff8dd02da1308d92ccb2fd/robocode.battle/src/main/java/net/sf/robocode/battle/peer/RobotPeer.java#L182 <code>println()</code>] method:

<syntaxhighlight lang="java">
public void println(String s) {
    synchronized (proxyText) {
        battleText.append(s);
        battleText.append("\n");
    }
}
</syntaxhighlight>

Note the following:
# Robocode is multithreaded. Heavy multithreading causes race conditions.
# The variable <code>battleText</code> is a <code>StringBuilder</code>, which is not thread-safe (unlike a <code>StringBuffer</code>), which is.
# The code modifies '''<code>battleText</code>''', but only synchronizes against '''<code>proxyText</code>'''.

Therefore, EvBotNG ''is'' skipping turns, but no log messages (from either Robocode or the bot) are printed, because they are silently dropped due to race conditions in the <code>println()</code> method. The only thing you ultimately see is the ThreadDeath exception caused by <code>Thread.stop()</code> forcibly terminating the thread.

Presumably, this occurs because of unlucky interaction between <code>RobotPeer.println()</code> and [https://github.com/robo-code/robocode/blob/0eb93ba532bc6731b7ff8dd02da1308d92ccb2fd/robocode.battle/src/main/java/net/sf/robocode/battle/peer/RobotPeer.java#L195 <code>RobotPeer.readOutText()</code>].

<pre>
readOutText()                                 | println()
============================================= | ===============================
final String robotText =                      |
battleText.toString() + proxyText.toString(); |
                                              | battleText.append(s);
                                              | battleText.append("\n");
battleText.setLength(0);                      |
proxyText.setLength(0);                       |
return robotText;                             |
</pre>

Therefore, the solution is to add <code>synchronized(battleText) {</code> guards around <code>readOutText()</code> and <code>println()</code>.

Or maybe I'm way off track.