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package cbt
import java.util.concurrent.ConcurrentHashMap
private[cbt] class LockableKey
/**
A cache that lazily computes values if needed during lookup.
Locking occurs on the key, so separate keys can be looked up
simultaneously without a deadlock.
*/
final private[cbt] class KeyLockedLazyCache[Key <: AnyRef,Value <: AnyRef](
val keys: ConcurrentHashMap[Key,AnyRef],
val values: ConcurrentHashMap[AnyRef,Value],
logger: Option[Logger]
){
def get( key: Key, value: => Value ): Value = {
val lockableKey = keys.synchronized{
if( ! (keys containsKey key) ){
val lockableKey = new LockableKey
//logger.foreach(_.resolver("CACHE MISS: " ++ key.toString))
keys.put( key, lockableKey )
lockableKey
} else {
val lockableKey = keys get key
//logger.foreach(_.resolver("CACHE HIT: " ++ lockableKey.toString ++ " -> " ++ key.toString))
lockableKey
}
}
import collection.JavaConversions._
//logger.resolver("CACHE: \n" ++ keys.mkString("\n"))
// synchronizing on key only, so asking for a particular key does
// not block the whole cache, but just that cache entry
lockableKey.synchronized{
if( ! (values containsKey lockableKey) ){
values.put( lockableKey, value )
}
values get lockableKey
}
}
def update( key: Key, value: Value ): Value = {
val lockableKey = keys get key
lockableKey.synchronized{
values.put( lockableKey, value )
value
}
}
def remove( key: Key ) = keys.synchronized{
assert(keys containsKey key)
val lockableKey = keys get key
lockableKey.synchronized{
if(values containsKey lockableKey){
// this is so values in the process of being replaced (which mean they have a key but no value)
// are not being removed
keys.remove( key )
values.remove( lockableKey )
}
}
}
def containsKey( key: Key ) = keys.synchronized{
keys containsKey key
}
}
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