Parser Combinators and DynamicVariable combine to leak memory

[scabug]

I ran into a problem recently where, if I created and used a lot of Parser objects in a single thread, my application would OOM. Looking at the heap dump, I saw that that thread had thousands of inheritable thread locals, each of which had a DynamicVariable that held a reference to a Parser$Failure object, keeping my parser alive.

This DynamicVariable was introduced by the fix in #4929, specifically scala/scala@dce6b34

I'm not familiar with DynamicVariable so I don't know if the behavior I'm seeing is a bug in DynamicVariable or a bug in how the parser libraries use DynamicVariable - all I know is that, in this instance, they're combining to keep objects alive in a way that the garbage collector apparently can't see through.

I'm attaching a file to reproduce it; compile the file, then do

   JAVA_OPTS="-verbose:gc -Xmx256m -Xms64m -XX:+UseCompressedOops -XX:+HeapDumpOnOutOfMemoryError" scala ParserLoop

and you'll have a heap dump in short order.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-9010?orig=1
Reporter: David Carlton (davidcarltonsumo)
Affected Versions: 2.11.4
See #4929
Attachments:

• ParserLoop.scala (created on Nov 27, 2014 2:33:41 AM UTC, 2444 bytes)

[scabug]

@SethTisue said:
The parser combinators library is now community-maintained. Issues with it are now tracked at scala/scala-parser-combinators#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.

[scabug]

@SethTisue said (edited on Jul 18, 2015 12:36:45 AM UTC):
there is a PR for this, needing review, at scala/scala-parser-combinators#59

[Philippus]

this was fixed in scala/scala-parser-combinators#69