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From "Oliver Heger (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LANG-609) Support lazy initialization using atomic variables
Date Sat, 20 Mar 2010 20:40:27 GMT

    [ https://issues.apache.org/jira/browse/LANG-609?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12847820#action_12847820
] 

Oliver Heger commented on LANG-609:
-----------------------------------

The {{get()}} method in the {{ConcurrentInitializer}} interface now throws a {{ConcurrentException}}.
This is a checked exception and forces client code to always catch and handle the exception.

LANG-610 proposes a new {{ConcurrentRuntimeException}} class which is an unchecked exception.
It would be nice if the checked exception could automatically be transformed into the unchecked
exception. To achieve this we could add convenience methods for the handling of initializers
to {{ConcurrentUtils}}, e.g.:

{code}
public static <T> T initialize(ConcurrentInitializer<T> initializer) throws ConcurrentException;

public static <T> T initializeUnchecked(ConcurrentInitializer<T> initializer);
{code}

These methods could also be null-safe. The first variant would simply invoke the passed in
{{ConcurrentInitializer}}. The second one would catch a {{ConcurrentException}} and transform
it to a {{ConcurrentRuntimeException}}.

> Support lazy initialization using atomic variables
> --------------------------------------------------
>
>                 Key: LANG-609
>                 URL: https://issues.apache.org/jira/browse/LANG-609
>             Project: Commons Lang
>          Issue Type: New Feature
>          Components: lang.concurrent.*
>            Reporter: Oliver Heger
>            Priority: Minor
>             Fix For: 3.0
>
>         Attachments: AtomicInitializer.patch
>
>
> In the new concurrent package there is already the {{LazyInitializer}} class implementing
the double-check idiom for lazy initialization of instance fields. Another way to perform
initialization lazily would be the usage of atomic variables. This solution would not need
synchronization at all. If there is low contention (not many threads in parallel), it is more
efficient than synchronized access. Its drawback is that the initialization may be done multiple
times if multiple threads access the initializer almost at the same time (however, it can
be guaranteed that always the same object created by the initializer is returned).
> This is a proposal to add an {{AtomicInitializer}} class as an alternative to {{LazyInitializer}}
that operates on {{AtomicReference}} variables.
> In order to make the initializers smoothly exchangable, it would make sense for them
to share a common interface. This interface could also be implemented by the {{BackgroundInitializer}}
class.

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