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https://issues.apache.org/jira/browse/CASSANDRA-700?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jeff Hodges updated CASSANDRA-700:
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Attachment: 0001-removing-lots-of-static-instance-methods.patch
Here's a version of the patch without the MessagingService changes. I'm not
sure that the current design of MessagingService is ideal, but it's best not to
refactor it for this ticket.
> Replacing the many forms of singleton instance methods
> ------------------------------------------------------
>
> Key: CASSANDRA-700
> URL: https://issues.apache.org/jira/browse/CASSANDRA-700
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Jeff Hodges
> Attachments:
> 0001-MessagingService.instance-MessagingService.instance.patch,
> 0001-removing-lots-of-static-instance-methods.patch,
> 0001-squashed-singleton-clean-up.patch,
> 0002-HintedHandOffManager.instance-HintedHandOffManager.i.patch,
> 0003-StorageService.instance-StorageService.instance.patch,
> 0004-AntiEntropyService.instance-AntiEntropyService.insta.patch,
> 0005-Gossiper.instance-Gossiper.instance.patch,
> 0006-StorageLoadBalancer.instance-StorageLoadBalancer.ins.patch,
> 0007-FailureDetector.instance-FailureDetector.instance.patch,
> 0008-ReadRepairManager.instance-ReadRepairManager.instanc.patch
>
>
> In many places, the Cassandra codebase attempts to allow for only one
> instance of a particular class per process. It does so in a variety of ways,
> some of which are attempts at being thread-safe (with mixed results) while
> others seem to just delay instantiation.
> This issue is to track the changes necessary to consolidate these many forms
> of singleton into one form.
> What's interesting is that Java has a nice way of providing this facility in
> a very Java-y way. We can create a public static variable (called, say,
> instance) and, in the class definition, set it to a new instance of the very
> class we are in. We then can protect the class's constructor to prevent
> others from trying to use it. This allows us to have only one instance of the
> variable accessible only through the a static variable on the class itself.
> This is thread-safe because class definitions in Java is thread-safe. This is
> lazily loaded because Java doesn't do class definition until the first time
> the class is referenced in any way. Basically, this is everything that was
> attempted with the various static instance() methods but with complete
> success.
> The current classes I was able to find that can benefit from this are:
> AntiEntropyService
> FailureDetector
> Gossiper
> HintedHandOffManager
> MessagingService
> ReadRepairManager
> StorageLoadBalancer
> StorageService
> Other classes with similar constructions would be nice to remove, too.
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