Concurrency problem with _lastline in LCDSocketPoller

[antoneliasson]

I've observed crashes like the following:

sep 17 11:08:19 raspberrypi java[537]: Exception in thread "Thread-1" java.lang.NullPointerException
sep 17 11:08:19 raspberrypi java[537]: at java.util.regex.Matcher.getTextLength(Matcher.java:1283)
sep 17 11:08:19 raspberrypi java[537]: at java.util.regex.Matcher.reset(Matcher.java:309)
sep 17 11:08:19 raspberrypi java[537]: at java.util.regex.Matcher.<init>(Matcher.java:229)
sep 17 11:08:19 raspberrypi java[537]: at java.util.regex.Pattern.matcher(Pattern.java:1093)
sep 17 11:08:19 raspberrypi java[537]: at org.boncey.lcdjava.LCDSocketPoller.run(LCDSocketPoller.java:90)
sep 17 11:08:19 raspberrypi java[537]: [main] INFO org.boncey.lcdjava.LCD - Connected

Looking inside LCDSocketPoller, it's clear that access to _lastline is not concurrency correct. A different thread (inside LCD) can call getLastLine, setting it to null, while the LCDSocketPoller thread is reading _lastline inside the run() loop. This can cause it to be equal to null on line 90, even though there is a not-null-check on line 87.

Using org.boncey.lcdjava 0.5.0

[antoneliasson]

Work on this has started in the dev branch.