org.apache.hadoop.hbase.util

Class ConcurrentIndex<K,V>

java.lang.Object

org.apache.hadoop.hbase.util.ConcurrentIndex<K,V>

Type Parameters:

K - Key type

V - Value type

@InterfaceAudience.Private
 @InterfaceStability.Evolving
public class ConcurrentIndex<K,V>
extends Object

A simple concurrent map of sets. This is similar in concept to com.google.common.collect.Multiset, with the following exceptions:

• The set is thread-safe and concurrent: no external locking or synchronization is required. This is important for the use case where this class is used to index cached blocks by filename for their efficient eviction from cache when the file is closed or compacted.
• The expectation is that all entries may only be removed for a key once no more additions of values are being made under that key.

Constructor Summary

Constructors

Constructor and Description
ConcurrentIndex(<any> valueSetFactory) Creates an instance with a specified factory object for sets to be associated with a given key.

Method Summary

Modifier and Type	Method and Description
void	put(K key, V value) Associate a new unique value with a specified key.
boolean	remove(K key, V value) Removes the association between a specified key and value.
Set<V>	values(K key) Get all values associated with a specified key or null if no values are associated.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ConcurrentIndex

public ConcurrentIndex(<any> valueSetFactory)

Creates an instance with a specified factory object for sets to be associated with a given key.

Parameters:

valueSetFactory - The factory instance

Method Detail

put

public void put(K key,
                V value)

Associate a new unique value with a specified key. Under the covers, the method employs optimistic concurrency: if no set is associated with a given key, we create a new set; if another thread comes in, creates, and associates a set with the same key in the mean-time, we simply add the value to the already created set.

Parameters:

key - The key

value - An additional unique value we want to associate with a key

values

public Set<V> values(K key)

Get all values associated with a specified key or null if no values are associated. Note: if the caller wishes to add or removes values to under the specified as they're iterating through the returned value, they should make a defensive copy; otherwise, a ConcurrentModificationException may be thrown.

Parameters:

key - The key

Returns:

All values associated with the specified key or null if no values are associated with the key.

remove

public boolean remove(K key,
                      V value)

Removes the association between a specified key and value. If as a result of removing a value a set becomes empty, we remove the given set from the mapping as well.

Parameters:

key - The specified key

value - The value to disassociate with the key