org.apache.sis.util.collection

Interface Cache.Handler<V>

Type Parameters:

V - the type of value objects.

Enclosing class:

Cache<K,V>

public static interface Cache.Handler<V>

The handler returned by Cache.lock(K), to be used for unlocking and storing the result. This handler should be used as below (note the try … catch blocks, which are mandatory):

Value V = null;
Cache.Handler<V> handler = cache.lock(key);
try {
    value = handler.peek();
    if (value == null) {
        value = createMyObject(key);
    }
} finally {
    handler.putAndUnlock(value);
}

See the Cache javadoc for a more complete example.

Since:

0.3

Defined in the sis-utility module

Method Summary

Modifier and Type	Method and Description
V	peek() If the value is already in the cache, returns it.
void	putAndUnlock(V result) Stores the given value in the cache and release the lock.

Method Detail

peek

V peek()

If the value is already in the cache, returns it. Otherwise returns null. This method should be invoked after the Handler creation in case a value has been computed in an other thread.

Returns:

the value from the cache, or null if none.

putAndUnlock

void putAndUnlock(V result)
           throws IllegalStateException

Stores the given value in the cache and release the lock. This method must be invoked in a finally block, no matter what the result is.

Parameters:

result - the result to store in the cache, or null for removing the entry from the cache. If an entry is removed, a new computation will be attempted the next time a handler is created for the same key.

Throws:

Illegal­State­Exception - may be thrown if this method is not invoked in the pattern described in class javadoc, or if a key collision occurs.