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https://issues.apache.org/jira/browse/GROOVY-7407?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15923810#comment-15923810
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Jex Jexler commented on GROOVY-7407:
------------------------------------
The ConcurrentModificationException of
stacktrace-GrapeAndGroovyShellConcurrencyTest-1.txt is because Ivy's
MessageLoggerHelper is not thread-safe, it iterates over lists that can be
modified during iteration by other threads, in the test cases iteration was
over lists in MessageLoggerEngine. After wrapping the 3 member lists of
MessageLoggerEngine with Collections.synchronizedList(...) and making copies
before iterating over the lists in MessageLoggerHelper I get the following
behavior: Both test cases log many messages "unknown resolver null" (which can
a priori come from different places in Ivy) and the
GroovyCompileConcurrencyTest so far always fails with the
stacktrace-GroovyCompileConcurrencyTest-1.txt, i.e. it cannot resolve Guava's
Ascii class, presumably because something else is not thread-safe. (After my
changes I cannot reproduce exceptions in the other test,
GrapeAndGroovyShellConcurrencyTest.java, anymore so far, so it appears as if
the logged errors are not fatal.
> Compilation not thread safe if Grape / Ivy is used in Groovy scripts
> --------------------------------------------------------------------
>
> Key: GROOVY-7407
> URL: https://issues.apache.org/jira/browse/GROOVY-7407
> Project: Groovy
> Issue Type: Bug
> Components: Compiler, Grape
> Affects Versions: 2.4.3
> Environment: Essentially independent of the environment, as long as
> Groovy scripts use Grape; also this bug seems to be present since at least
> Groovy 1.7.5.
> Reporter: Jex Jexler
> Priority: Minor
> Labels: Compile, Grape, Groovy, Ivy
> Attachments: GrapeAndGroovyShellConcurrencyTest.java,
> GroovyCompileConcurrencyTest.java,
> stacktrace-GrapeAndGroovyShellConcurrencyTest-1.txt,
> stacktrace-GrapeAndGroovyShellConcurrencyTest-2.txt,
> stacktrace-GroovyCompileConcurrencyTest-1.txt,
> stacktrace-GroovyCompileConcurrencyTest-2.txt,
> WorkaroundGroovy7407WrappingGrapeEngine.java
>
>
> If Groovy scripts that import the same libraries via Grape are compiled in
> separate threads, compilation may fail due to race conditions.
> This does not happen if several threads use the *same* instance of
> GroovyClassLoader (GCL), because parseClass() uses synchronization.
> But as soon as different GCLs are used in separate threads or if the compiler
> is used directly (CompilationUnit.compile()), the issue occurs and
> compilation can fail.
> Two Java unit tests have be attached, which reproduce the issue, although
> this cannot be guaranteed with 100% certainty, because there is a race
> condition.
> Two different stacktraces have been observed for each unit test (with origins
> in Grape and in Ivy), which have also been attached (plus in a different
> environment (Tomcat webapp CentOS) once a an exception down in Ivy had been
> observed that seemed to be related to unzipping a JAR file, but no precise
> record of that exists any more).
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