[jira] [Created] (CALCITE-4986) Make HepProgram thread-safe

["Julian Hyde (Jira)" <ji...@apache.org>]

Julian Hyde created CALCITE-4986:
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             Summary: Make HepProgram thread-safe
                 Key: CALCITE-4986
                 URL: https://issues.apache.org/jira/browse/CALCITE-4986
             Project: Calcite
          Issue Type: Bug
            Reporter: Julian Hyde


{{HepProgram}} uses mutable fields for its working state and is therefore not thread-safe. If two threads are planning queries simultaneously and are using the same {{HepProgram}} instances they might conflict with each other. I suspect that this happens several times in Calcite's standard set of rules.

This change would move the mutable state out of {{HepProgram}}, so that {{HepProgram}} is fully immutable and therefore thread-safe.

It would also modernize some of the internals; for instance, {{class HepInstruction.MatchLimit}} has a field {{int limit}} that could be made final and assigned in the constructor. 



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