I'm looking for a modern implementation of an object pool in Java. I can see the apache commons one, but to be honest, I'd rather one that uses generics, and the concurrency stuff from more recent versions of java.
Does the commons pool really work well? The code looks pretty, erm, ugly.
I'd need something that allows custom liveness validation etc etc.
Thanks!
I can see the apache commons one, but to be honest, I'd rather one that uses generics, and the concurrency stuff from more recent versions of java.
Well, the fact is that this kind of projects (generic object pools) don't get much traction because there is little need for them nowadays (object creation is cheap). This probably explains why you don't see much of them (and actually, I'm only aware of Commons Pool).
That being said, if generics is your primary concern, you could patch Commons Pool, see POOL-83, it has a patch attached.
Does the commons pool really work well? The code looks pretty, erm, ugly.
It does have a few known bugs (four) but, to my knowledge, it works. And regarding the last sentence, well, if you think you can write something better, and if you have the time for that, why not just doing it?
I'd need something that allows custom liveness validation etc etc.
You don't have an infinite number of options. Either
Commons Pool is a good candidate for your project.
It's hard to make a recommendation without knowing what features you need.
If the number of objects in the pool is fixed, you can use a BlockingQueue as in this example from the question mentioned by @codedevour
If the values you want to pool can be associated with a key, you can use MapMaker from Guava
ConcurrentMap<Key, Connection> connections = new MapMaker()
.concurrencyLevel(32)
.softKeys()
.weakValues()
.expiration(30, TimeUnit.MINUTES)
.evictionListener(
new MapEvictionListener<Key, Connection>() {
public onEviction(Key key, Connection connection) {
connection.close();
}
});
.makeComputingMap(
new Function<Key, Connection>() {
public Connection apply(Key key) {
return createConnection(key);
}
});
Checkout KBOP. It's a thread safe blocking single key to single object or single key to multi object pool. It's lightweight and add no extra dependencies.
Yet another pool (yapool) contains a generic pool implementation with the option to act on pool events via listeners (example). This provides a lot of flexibility in customizing pool behavior, add functions and diagnosing pool resource usage. Alternatively, you can also extend a pool implementation to add your own desired behavior (example). This should be relatively straightforward since pool implementations already extend each other (Basic --> Bound --> Pruned).
To start, you can use a simple BoundPool and set your own factory (see for example the "LongFactory" in the earlier mentioned pool events example), or just use an ObjectPool.
Yapool has no "synchronized" blocks and is pretty fast.
This seems to be related to your question, maybe you should really consider to write a object pool by your own. Does this basic Java object pool work?.
Pooling was initially introduced as a tuning action for the slow performance of object creation and garbage collection in particular. On a modern JVM > 1.4 pooling is no more needed for the optimization of memory management in a typical business application. It can even have a negative effect on the garbage collector performance. In special cases, like creating millions of instances in every method call, it could still pay off.
Instance pooling, however is still interesting for objects with slow custom "post construction". In some cases you want to inject some dependencies after the object creation, read some configuration etc. This can be slow and doesn't have to be performed over and over again. In such cases object pooling will improve the overall performance.
Adam Bien -- Object Pooling Can Be Still Useful - For Entirely Different Reasons
What do you think of enhancing the commons Pool Framework? You could do some refactoring and add the generic part, would be nice for others too.
There is a object pool implementation in http://code.google.com/p/spf4j/ I find it a better implementation than the one in apache commons. Code is not so ugly, and it performs better...
For the generics side, why not just use the non-generic library, and create a wrapper that you use to access the non-generic library that takes care of the casting? That way there's a single place where the casting is done, which will at least clean up the code a bit.
To pool is the traditional way, to cache is the modern way. And there are many modern implementation of cache out there.
To learn the different between those two, you can read this: http://www.informit.com/guides/content.aspx?g=java&seqNum=104
My view is, we can use a cache library to pool our objects but not the other way around. Just don't forget to re-initialize the object after we get it from the cache. So why bother having two different animals (cache and pool) if you can achieve all just using one?
