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From "Oliver Heger (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LANG-609) Support lazy initialization using atomic variables
Date Sat, 02 Oct 2010 15:39:34 GMT

    [ https://issues.apache.org/jira/browse/LANG-609?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12917205#action_12917205
] 

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

Maybe there is room for all of these variants?

{{AtomicInitializer}} as it is now may be appropriate for use cases where multiple invocations
of the {{initialize()}} method are not an issue. In such scenarios it is the most efficient
variant.

The code proposed here could be added as a new class, say {{AtomicSafeInitializer}}. It has
a bit more overhead, but guarantees the one-time initialization.

I am not sure how this {{AtomicSafeInitializer}} compares to the {{LazyInitializer}} implementation
which is based on volatile variables and synchronization. I assume it will be more efficient
under low or moderate load. If there are many thread trying to initialize the object concurrently,
the synchronization approach might be preferrable. But this certainly depends on multiple
factors, and users should do benchmarks in their concrete environment before they take a decision.

So would you agree to add this code as a new {{AtomicSafeInitializer}} class? Other preferences
for the name?

> 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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