[concurrency-interest] Measuring and expressing contention

Chris Vest mr.chrisvest at gmail.com
Tue Jul 22 03:08:32 EDT 2014

Hi Jeff,

I already use ThreadLocals to reduce contention, though it does something simpler than what you describe, and does not require threads to each grab their own client/proxy/facade:

The pool is designed for relatively expensive-to-allocate objects, such as network connections, so I assume that normal allocation will always be slower in the use cases the pool is applied to.


I know about HdrHistogram, but I think it ought to be possible to do something simpler than that, when the goal is answering the question “Is the pool big enough?"


On 22 Jul 2014, at 00:31, Jeff Hain <jeffhain at rocketmail.com> wrote:

> Hi Chris.
> >So, do you have any experience with solving something like this, or ideas for how to approach it?
> For the pure "contention" part (not starvation or measurement),
> if you are ok with some spare instances that would not be counted
> in your shared pool, what you can do is have thread-local buffers
> of instances as proxies (threads would only see the pool through them),
> and give them a max size of 100 or 1000 for example.
> When a proxy gets empty, you half-fill it (in one shot of synchronization or alike),
> and when it gets full you half-empty it ("half-" to reduce risk of flip-flop between full
> and empty).
> It can greatly reduce contention on the shared pool, and helps with thread
> locality (when you put an instance in thread-local proxy, and then retrieves
> the same instance from it).
> If you use smart policies like timing etc. in your pools, make sure your pooling
> still helps - I found it hard enough to beat GC throughput with pooling
> even without this overhead.
> -Jeff
> PS : In my experience the most vicious bugs come from either threading or pooling,
> so having a way to easily deactivate all your pools (i.e. use pools that actually don't pool)
> can help a lot.

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