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From "Blake Eggleston (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-7841) Pass static singleton instances into constructors of dependent classes
Date Thu, 04 Sep 2014 23:52:24 GMT


Blake Eggleston commented on CASSANDRA-7841:

I have a couple issues I could use some input on. You can check out my current progress here:

1) StorageService & TokenMetadata: A lot the singletons StorageService depends on also
depend on StorageService, but only for access to the tokenMetadata, versionedValueFactory,
and bootstrap status. In my experimental implementation, I split this stuff into a separate
class called ClusterState, which StorageService, and several other classes depended on. I'm
reaching a point where I'm going to have to do something similar, and wanted to get some input
on the specifics. Initially, I was thinking of just duplicating the ClusterState class, but
then thought that having separate singletons for the TokenMetaData, and VersionedValueFactory,
and moving the bootstrap status into the DatabaseDescriptor might be more flexible. I'm not
sure that the 3 necessarily need to be kept together.

2) Interface implementations: IAuthorizer, IEndpoint snitch, and a few others all have implementations
with different sets of dependencies, which they will need to be instantiated with. I know
that an autowired DI framework isn't something we want to do for DI in general, but it seems
like it's the right thing to use in these cases. I'm not married to the idea, but the only
alternatives I can think of at this point would be to check for a single ultraconstructor
which takes all possible dependencies, or using reflection to work out which constructors
are available, and passing the dependencies in that way, something the DI frameworks already
do better than an ad-hoc implementation. Here are some of the IEndpointSnitch and ReplicationStrategy
classes, and their dependencies:

> Pass static singleton instances into constructors of dependent classes
> ----------------------------------------------------------------------
>                 Key: CASSANDRA-7841
>                 URL:
>             Project: Cassandra
>          Issue Type: Sub-task
>            Reporter: Blake Eggleston
>            Assignee: Blake Eggleston
> Identify all non-singleton usages of static state (grep for '.instance.'), and refactor
to pass dependencies into their constructors from their instantiating services.

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