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Date: Sat, 7 May 2011 01:13:03 +0000 (UTC)
From: "Daniel Dai (JIRA)" <jira@apache.org>
To: pig-dev@hadoop.apache.org
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Subject: [jira] [Commented] (PIG-1821) UDFContext.getUDFProperties does not
 handle collisions in hashcode of udf classname (+ arg hashcodes)
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    [ https://issues.apache.org/jira/browse/PIG-1821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13030243#comment-13030243 ] 

Daniel Dai commented on PIG-1821:
---------------------------------

+1

> UDFContext.getUDFProperties does not handle collisions in hashcode of udf classname (+ arg hashcodes)
> -----------------------------------------------------------------------------------------------------
>
>                 Key: PIG-1821
>                 URL: https://issues.apache.org/jira/browse/PIG-1821
>             Project: Pig
>          Issue Type: Bug
>    Affects Versions: 0.8.0
>            Reporter: Thejas M Nair
>            Assignee: Thejas M Nair
>             Fix For: 0.9.0
>
>         Attachments: PIG-1821.1.patch, PIG-1821.2.patch, PIG-1821.3.patch
>
>
> In code below, if generateKey() returns same value for two udfs, the udfs would end up sharing the properties object. 
> {code}
> private HashMap<Integer, Properties> udfConfs = new HashMap<Integer, Properties>();
>     public Properties getUDFProperties(Class c) {
>         Integer k = generateKey(c);
>         Properties p = udfConfs.get(k);
>         if (p == null) {
>             p = new Properties();
>             udfConfs.put(k, p);
>         }
>         return p;
>     }
>     private int generateKey(Class c) {
>         return c.getName().hashCode();
>     }
>     public Properties getUDFProperties(Class c, String[] args) {
>         Integer k = generateKey(c, args);
>         Properties p = udfConfs.get(k);
>         if (p == null) {
>             p = new Properties();
>             udfConfs.put(k, p);
>         }
>         return p;
>     }
>     private int generateKey(Class c, String[] args) {
>         int hc = c.getName().hashCode();
>         for (int i = 0; i < args.length; i++) {
>             hc <<= 1;
>             hc ^= args[i].hashCode();
>         }
>         return hc;
>     }
> {code}
> To prevent this, a new class (say X) that can hold the classname and args should be created, and instead of HashMap<Integer, Properties>,  HashMap<X, Properties> should be used. Then HahsMap will deal with the collisions. 

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