at.molindo.utils.concurrent
Class KeyLock<K,V>

java.lang.Object
  at.molindo.utils.concurrent.KeyLock<K,V>

Type Parameters:

K - key type

V - return type of Callable

public class KeyLock<K,V>
extends Object

concurrency utility that locks execution of callable by a key, i.e. not using key's identity but equality.

Author:

stf@molindo.at

Nested Class Summary

static class

KeyLock.KeyLockedException

Constructor Summary

KeyLock()

KeyLock(boolean wait)

Method Summary

int	activeCount()
List<K>	activeKeys()
static <K,V> KeyLock<K,V>	newKeyLock()
static <K,V> KeyLock<K,V>	newKeyLock(boolean wait)
protected V	replace(V result, Exception ex) how to replace already computed results.
V	withLock(K key, Callable<? extends V> callable) execute callable while locking concurrent execution for key

Methods inherited from class java.lang.Object

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

Constructor Detail

KeyLock

public KeyLock()

KeyLock

public KeyLock(boolean wait)

Parameters:

wait - should withLock(Object, Callable) calls wait for concurrent calls to finish or should they fail fast

Method Detail

newKeyLock

public static <K,V> KeyLock<K,V> newKeyLock()

newKeyLock

public static <K,V> KeyLock<K,V> newKeyLock(boolean wait)

withLock

public V withLock(K key,
                  Callable<? extends V> callable)
           throws Exception

execute callable while locking concurrent execution for key

Parameters:

key -

callable -

Returns:

Throws:

KeyLock.KeyLockedException - only if key lock configured not to wait and key locked by other thread

KeyLock.KeyLockedException - any exception thrown by callable.call()

NullPointerException - if key or callable are null

Exception

replace

protected V replace(V result,
                    Exception ex)
             throws Exception

how to replace already computed results. by default it's null, as users might not want to get concurrency issues on shared results. As a replacement, one could perform a DB lookup if the task is to create/update a DB entity or do a deep clone of the object.

Parameters:

result -

ex -

Returns:

Throws:

Exception

activeCount

public int activeCount()

Returns:

number of active keys

activeKeys

public List<K> activeKeys()

Returns:

a newly created List of all active keys. Changes to this list don't have any effect to this KeyLock (changes to the values will have an undefined effect though).