Re: [cp-patches] FYI: Implemented an ObjectPool

[Roman Kennke]

Hi,

> > I implemented and added an ObjectPool class.
> 
> Please measure! Don't assume that this will lead to better performance.
> I do follow your reasoning. But ultimately this is the job of the
> allocator/garbage collector.

I completely agree with you that ideally this should be done in the GC.
This is why I hestitate to actually introduce some 'optimizations'. I
don't know about the current situation in free VMs Garbage Collectors
and how the impact would be. It would be helpful if some VM hackers
could comment on the issue.

> Please make it really easy to turn on/off caching so people can do real
> measurements of the performance impact.

I have added a flag in the ObjectPool that can turn off the cache. As
well as some counters that count how many objects are
requested/returned/created/pooled. This is not a very clever benchmark,
since it does not actually measure performance (time-wise).

>  And only introduce it when it is
> a clear win.

Seeing that it is quite difficult to find the right spots where objects
should actually be returned into the pool, I strongly hesitate now to
introduce anything.

> What seems to happen a lot in larger projects is that someone introduces
> some pooling/caching of certain constructs and when some implementation
> detail somewhere else in the stack changes the pooling/caching isn't
> revised/remeasured to see if it still makes sense (or that it actually
> decreases performance given the new circumstances!).
> Don't let that happen in this case.

I won't. It would be nice if some folks would play a little and comment
on this issue. Note that the pool isn't actually in use in Classpath, it
only sits around now for testing. I committed the following changes that
could help benchmarking:

2005-07-01  Roman Kennke  <address@hidden>

        * gnu/classpath/ObjectPool.java:
        Introduced flag for turning on/off caching.
        (getInstance): Synchronized access to this method.
        (borrowObject): Synchronized access to the pool.
        Added some benchmarking statements.
        (returnObject): Synchronized access to the pool.
        Added some benchmarking statements.
        (createObject): Synchronized access to the pool.
        Added some benchmarking statements.
        (printStats): New method. Prints out some stats about the pool
        usage.

/Roman

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