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GeezerVison is showing github.com — Concurrency problem with _lastline in LCDSocketPoller · Issue #4 · lcdproc/lcdjava

Concurrency problem with _lastline in LCDSocketPoller #4

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Concurrency problem with _lastline in LCDSocketPoller#4
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@antoneliasson
antoneliasson
opened on Sep 17, 2016
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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

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  1. antoneliasson commented on Oct 2, 2016

    @antoneliasson
    antoneliasson
    on Oct 2, 2016
    CollaboratorAuthor
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    Work on this has started in the dev branch.

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