[jira] Updated: (AVRO-261) Allow Schemas to be immutable

["Thiruvalluvan M. G. (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/AVRO-261?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Thiruvalluvan M. G. updated AVRO-261:
-------------------------------------

    Attachment: AVRO-261.patch

Here is a patch which addresses this issue. The Schema we have had was almost immutable except a few things.

   - Union and Enum schemas stored references to Lists supplied to their constructors. So if the original Lists were modified, the schema would get affected. A simple fix is to make a fresh list. But these schemas also return the List through getter methods, opening them up for updates. The solution is to store an unmodifiable wrapper around the fresh list. If we are sure that the original list is not available for modification, we can simply wrap the list itself without constructing a new one.
   - Similar things happened in RecordSchema's _fields_ and _fieldSchemas_ attributes. But these collections were already constructed afresh in setFields() method. So we just need to make these unmodifiable.
   - We need extra protection against setFields() being called more than once. I applied Kevin's idea having a boolean variable _locked_. It would have been nice if we can completely avoided setFields(). To avoid setFields() we need to set the fields in the constructor. But we cannot do that because we need to construct the RecordSchema and add to the _names_ map before we can fully construct its fields. This is necessary to handle recursive schemas.
   - The Field class had a non-final field _position_. But it is private and there is already protection that it cannot be modified more than once. So nothing needs to be done there.
   

> Allow Schemas to be immutable
> -----------------------------
>
>                 Key: AVRO-261
>                 URL: https://issues.apache.org/jira/browse/AVRO-261
>             Project: Avro
>          Issue Type: New Feature
>          Components: java
>            Reporter: Kevin Oliver
>            Priority: Minor
>         Attachments: AVRO-261.patch
>
>
> It would be nice if there was the ability to have an immutable Schema in java. 
> Without this, it makes sharing schemas risky. Also, with this, we could (lazily) cache the hashCode which is a fairly expensive operation today, especially on something like a record.

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