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From Cory Klein <coryfkl...@gmail.com>
Subject [POOL] Improving the borrow/return process with anonymous functions
Date Thu, 12 Nov 2015 17:46:57 GMT
First off, hello! My name is Cory Klein and this marks my first
interaction with this group. I've read through the email guidelines
and I think I have something productive to discuss here.

In looking at GenericObjectPool I came across a process that I believe
could be improved upon and I wanted to get some early feedback on this
approach before investing the time to create a full pull request.

The general approach for using an object pool is to borrow an object,
use it to do something, and then return it. For example:

Resource resource = objectPool.borrowObject();
String result = doSomething(resource);
objectPool.returnObject(resource);

In this case, objectPool owns instances of Resource and lends them
out. However, the object pool abstraction gets slightly leaky when you
consider that the consumer has a responsibility to return the object,
and other consumers might be adversely affected if objects aren't
returned properly.

I propose augmenting ObjectPool with the following method. This code
is merely demonstrative and not intended to be final:

public class <T> ObjectPool {
    ...

    public R run(Function<T,R> function) {
        T obj = null;
        try {
            obj = borrowObject();
        } catch (Exception e) {
            throw new RuntimeException("Unable to get object from pool");
        }
        R returnVal = null;
        try {
            returnVal = function(T);
        } catch (Exception e) {
            throw new RuntimeException("Supplied lambda produced an exception");
        } finally {
            this.returnObject(obj);
            return returnVal;
        }
    }
}

With this idea, consumers can instead provide the object pool with a
function to run using the required resource, leaving the object pool
complete ownership of the resource and ensuring that resources can
always be returned to the pool. The borrow/return example from above
becomes merely:

String result = objectPool.run((resource) -> doSomething(resource));

In summary, some positive reasons I can think of to make this change are:

* Improve a leaky abstraction
* Less code needed on the consuming side
* Improved reliability

I'm having a harder time coming up with reasons why this change is
bad, but I think this may be due to a lack of intimacy with the
library as it exists now. Are there any reasons that are immediately
apparent to you?

Thanks,

Cory Klein

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