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From "Benedict (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-7705) Safer Resource Management
Date Sun, 14 Sep 2014 06:36:33 GMT


Benedict commented on CASSANDRA-7705:

Patch available [here|]

This patch traps reference leaks as well as double-releasing references. This version only
modifies SSTableReader resource management, but it can be rolled out for any heavy-weight
objects we manage, i.e. all instances of RefCountedMemory except those stored in SerializingCache.

> Safer Resource Management
> -------------------------
>                 Key: CASSANDRA-7705
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Benedict
>             Fix For: 3.0
> We've had a spate of bugs recently with bad reference counting. these can have potentially
dire consequences, generally either randomly deleting data or giving us infinite loops. 
> Since in 2.1 we only reference count resources that are relatively expensive and infrequently
managed (or in places where this safety is probably not as necessary, e.g. SerializingCache),
we could without any negative consequences (and only slight code complexity) introduce a safer
resource management scheme for these more expensive/infrequent actions.
> Basically, I propose when we want to acquire a resource we allocate an object that manages
the reference. This can only be released once; if it is released twice, we fail immediately
at the second release, reporting where the bug is (rather than letting it continue fine until
the next correct release corrupts the count). The reference counter remains the same, but
we obtain guarantees that the reference count itself is never badly maintained, although code
using it could mistakenly release its own handle early (typically this is only an issue when
cleaning up after a failure, in which case under the new scheme this would be an innocuous

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