Cache.Handler (Apache SIS 1.0 API)

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 (the try … finally statements are important):
```
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

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	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.