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From "Henri Biestro (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JEXL-97) JEXL parses long expressions with lots of parenthesis slowly
Date Thu, 11 Feb 2010 08:08:28 GMT

    [ https://issues.apache.org/jira/browse/JEXL-97?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12832418#action_12832418
] 

Henri Biestro commented on JEXL-97:
-----------------------------------

I've been trying to reproduce this behavior on 2.x trunk with this code added as a method
in IssuesTest.java:
{code}
    public void test97() throws Exception {
        JexlContext ctxt = new MapContext();
        for(char v = 'a'; v <= 'z'; ++v) {
            ctxt.set(Character.toString(v), 10);
        }
        String input =
            "(((((((((((((((((((((((((z+y)/x)*w)-v)*u)/t)-s)*r)/q)+p)-o)*n)-m)+l)*k)+j)/i)+h)*g)+f)/e)+d)-c)/b)+a)";

        JexlEngine jexl = new JexlEngine();
        Expression script;
        // Make sure everything is loaded...
        long start = System.nanoTime();
        script = jexl.createExpression(input);
        Object value = script.evaluate(ctxt);
        assertEquals(Integer.valueOf(11), value);
        long end = System.nanoTime();
        System.out.printf("Parse took %.3f seconds\n", (end-start)/1e+9);
    }
{code}

Runs in .003s on my box (os x, 2.8Ghz, jdk1.5 and jdk1.6).
Can you check again and/or upload a modified test that exhibits the performance issue you
describe?
The code you originally posted can only run on JEXL1.x (ExpressionFactory does not exist in
jexl2).
Thanks


> JEXL parses long expressions with lots of parenthesis slowly
> ------------------------------------------------------------
>
>                 Key: JEXL-97
>                 URL: https://issues.apache.org/jira/browse/JEXL-97
>             Project: Commons JEXL
>          Issue Type: Bug
>    Affects Versions: 2.0, 1.1, 1.0
>         Environment: Java
>            Reporter: Jeff Ichnowski
>            Priority: Minor
>         Attachments: proposed.patch
>
>
> JEXL's parser uses an unbounded JavaCC LOOKAHEAD to distinguish assignment expressions
from other expressions.  The result is certain expressions take exponential time to parse.
 The example snippet below demonstrates the problem.  On my machine parsing the expression
below takes ~120 seconds.  Changing the parser to remove the LOOKAHEAD can get this to parse
in milliseconds.  The lookahead appears to be in all versions of the parser source.
> import org.apache.commons.jexl.Expression;
> import org.apache.commons.jexl.ExpressionFactory;
> public class SlowParse {
>     public static void main(String[] args) throws Exception {
>         String input = 
>             "(((((((((((((((((((((((((z+y)/x)*w)-v)*u)/t)-s)*r)/q)+p)-o)*n)-m)+l)*k)+j)/i)+h)*g)+f)/e)+d)-c)/b)+a)";
>         // Make sure everything is loaded...
>         Expression expr = ExpressionFactory.createExpression(input);
>         long start = System.nanoTime();
>         expr = ExpressionFactory.createExpression(input);
>         long end = System.nanoTime();
>         System.out.printf("Parse took %.1f seconds\n", (end-start)/1e+9);
>     }
> }

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