48 lines
1.8 KiB
Scala
48 lines
1.8 KiB
Scala
package com.twitter.tweetypie.caching
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import com.twitter.io.Buf
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import com.twitter.util.Time
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/**
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* How to store values of type V in cache. This includes whether a
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* given value is cacheable, how to serialize it, when it should
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* expire from cache, and how to interpret byte patterns from cache.
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*/
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trait ValueSerializer[V] {
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/**
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* Prepare the value for storage in cache. When a [[Some]] is
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* returned, the [[Buf]] should be a valid input to [[deserialize]]
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* and the [[Time]] will be used as the expiry in the memcached
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* command. When [[None]] is returned, it indicates that the value
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* cannot or should not be written back to cache.
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*
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* The most common use case for returning None is caching Try
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* values, where certain exceptional values encode a cacheable state
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* of a value. In particular, Throw(NotFound) is commonly used to
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* encode a missing value, and we usually want to cache those
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* negative lookups, but we don't want to cache e.g. a timeout
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* exception.
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*
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* @return a pair of expiry time for this cache entry and the bytes
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* to store in cache. If you do not want this value to explicitly
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* expire, use Time.Top as the expiry.
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*/
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def serialize(value: V): Option[(Time, Buf)]
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/**
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* Deserialize a value found in cache. This function converts the
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* bytes found in memcache to a [[CacheResult]]. In general, you
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* probably want to return [[CacheResult.Fresh]] or
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* [[CacheResult.Stale]], but you are free to return any of the
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* range of [[CacheResult]]s, depending on the behavior that you
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* want.
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*
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* This is a total function because in the common use case, the
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* bytes stored in cache will be appropriate for the
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* serializer. This method is free to throw any exception if the
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* bytes are not valid.
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*/
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def deserialize(serializedValue: Buf): CacheResult[V]
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}
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