Github user zsxwing commented on the pull request:
https://github.com/apache/spark/pull/8357#issuecomment-133793646
> Does DDLParser have the same issue?
I think we only create one `DDLParser` in on SQLContext. Right? It does
still leak one `ThreadLocal`, but I don't think people will create a lot of
`SQLContext`. If so, I think we should change all subclasses of
`scala.util.parsing.combinator.Parsers` in SQL to object.
> since SI-4929's resolution is "out of scope", can you add a pointer of
the comment saying parser combinator is thread safe in the description?
`SI-4929` was set to `out of scope` because this comment here
https://issues.scala-lang.org/browse/SI-4929?focusedCommentId=72968&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-72968
:
```
The parser combinators library is now community-maintained. Issues with it
are now tracked at https://github.com/scala/scala-parser-combinators/issues/61
instead of here in the Scala JIRA.
Interested community members: if you consider this issue significant, feel
free to open a new issue for it on GitHub, with links in both directions.
```
SI-4929 is really confusing because a lot of comments are about the memory
leak rather that the original thread-safe issue.
`scala.util.parsing.combinator.Parsers` has only one field
`lastNoSuccessVar`, which is `DynamicVariable` now. Of cause,
`scala.util.parsing.combinator.Parsers.Parser` is not thread-safe, but it's
created every time when parsing input, so that's safe.
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