org.apache.drill.exec.coord.store

Interface TransientStore<V>

All Superinterfaces:

AutoCloseable

All Known Implementing Classes:

BaseTransientStore, MapBackedStore, ZkEphemeralStore

public interface TransientStore<V>
extends AutoCloseable

An abstraction for storing, retrieving and observing transient (key, value) pairs in a distributed environment. This abstraction diverges from PersistentStore in that the lifetime of a (key, value) tuple is bound to the lifetime of the node originally creating it. In other words, entries are evicted as soon as node/s originally stored them leaves the cluster. That should explain the reason for relocating this abstraction under cluster coordination package. Consumers of this interface can observe changes made to the store via attaching a listener.

Method Summary

Modifier and Type	Method and Description
void	addListener(TransientStoreListener listener) Adds a listener that observes store events.
Iterator<Map.Entry<String,V>>	entries() Returns an iterator of (key, value) tuples.
V	get(String key) Returns a value corresponding to the given look-up key if exists, null otherwise.
Iterator<String>	keys() Returns an iterator of keys.
V	put(String key, V value) Stores the given (key, value) in this store overriding the existing value.
V	putIfAbsent(String key, V value) Stores the given (key, value) tuple in this store only if it does not exists.
V	remove(String key) Removes the (key, value) tuple from this store if the key exists.
void	removeListener(TransientStoreListener listener) Removes the given listener from this store if exists, has no effect otherwise.
int	size() Returns number of entries.
Iterator<V>	values() Returns an iterator of values.

Methods inherited from interface java.lang.AutoCloseable

close

Method Detail

get

V get(String key)

Returns a value corresponding to the given look-up key if exists, null otherwise.

Parameters:

key - look-up key

put

V put(String key,
      V value)

Stores the given (key, value) in this store overriding the existing value.

Parameters:

key - look-up key

value - value to store

Returns:

the old value if the key exists, null otherwise

putIfAbsent

V putIfAbsent(String key,
              V value)

Stores the given (key, value) tuple in this store only if it does not exists.

Parameters:

key - look-up key

value - value to store

Returns:

the old value if the key exists, null otherwise

remove

V remove(String key)

Removes the (key, value) tuple from this store if the key exists.

Parameters:

key - look-up key

Returns:

the removed value if key exists, null otherwise

entries

Iterator<Map.Entry<String,V>> entries()

Returns an iterator of (key, value) tuples.

keys

Iterator<String> keys()

Returns an iterator of keys.

values

Iterator<V> values()

Returns an iterator of values.

size

int size()

Returns number of entries.

addListener

void addListener(TransientStoreListener listener)

Adds a listener that observes store events. Note that i) Calling this method with the same listener instance more than once has no effect. ii) Listeners are not necessarily invoked from the calling thread. Consumer should consider thread safety issues. iii) Subclasses might hold a strong reference to the listener. It is important that consumer removes its listener once it is done observing events.

See Also:

removeListener(TransientStoreListener)

removeListener

void removeListener(TransientStoreListener listener)

Removes the given listener from this store if exists, has no effect otherwise.