javax.cache

Interface Cache.EntryProcessor<K,V,T>

Type Parameters:

K - the type of keys maintained by this cache

V - the type of cached values

Enclosing interface:

Cache<K,V>

public static interface Cache.EntryProcessor<K,V,T>

Allows execution of code which may mutate a cache entry with exclusive access (including reads) to that entry.

Any Cache.Entry mutations will not take effect till after the processor has completed; if an exception is thrown inside the processor, the exception will be returned wrapped in an CacheException. No changes will be made to the cache.

This enables a way to perform compound operations without transactions involving a cache entry atomically. Such operations may include mutations.

Implementations may process in situ, avoiding expensive network transfers. e.g. appending to a list. Another is computing a function on a value and returning just that.

Chaining & Recursion

An entry processor cannot invoke any cache operations, including other processor operations against another key.

However multiple EntryProcessors can be execute against the same key. For example an EntryProcessor might be a composite of entry processors or a chain of entry processors. The outermost EntryProcessor will lock and unlock the entry. todo define this behaviour more thoroughly.

Statistics

Invocation of an entry processor is regarded as a get operation for statistics purposes.

If Cache.MutableEntry.setValue(Object) is called in an EntryProcessor it is considered a put for statistics purposes.

CacheEntryListeners

As a result of an entry processor registered CacheEntryListeners are called.

Remote Invocation

If executed in a JVM remote from the one invoke was called in, an EntryProcessor equal to the local one will execute the invocation. For remote execution to succeed, the EntryProcessor implementation class must be in the executing class loader, as must K if Cache.Entry.getKey() is used and V if Cache.Entry.getValue() is invoked.

In order to simplify placement of EntryProcessors in remote JVMs, arguments can be passed separately. In such cases EntryProcessors do not need to be Serializable.

Author:

Greg Luck, Yannis Cosmadopoulos

Method Summary

Methods

Modifier and Type	Method and Description
T	process(Cache.MutableEntry<K,V> entry, Object... arguments) Process an entry.

Method Detail

process

T process(Cache.MutableEntry<K,V> entry,
        Object... arguments)

Process an entry. Exclusive read and write access to the entry is obtained to the entry.

Parameters:

entry - the entry

arguments - a number of arguments to the process.

Returns:

the result of the processing, if any, which is user defined.