[JEXL-274] Handle soft and hard stack overflow

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.1
• Fix Version/s: 3.2
• Assignee: Henri Biestro
• Reporter: Henri Biestro
• Created: 17/Sep/18 14:38
• Updated: 07/Jun/21 13:15
• Resolved: 18/Sep/18 16:41

Description

WHAT:
Since JEXL allows recursion, it would be convenient to stop execution early when running towards a stack overflow. In general, scripts don't have much use for recursion so this would be a good (soft) safeguard.
Incidentally, when a function called by a script ends up in a stack overflow, it would be nice to catch it and properly propagate it through a JexlException.
HOW:
Introduce a new JexlException subclass (StackOverflow) that can be thrown after catching a (JVM) StackOverflow in Interpreter.interpret().
The StackOverflow soft limit -ie one that pertains to JEXL only - requires a new JexlBuilder option (stackOverflow(size)) and a way to count the stack 'height'; easiest/safest seems to put interpreter instance in TLS and increment/check a 'frame pointer' member.