XOM API for Processing XML with Java

[Wolfgang Hoschek <whoschek AT lbl.gov>]

> > My 2 cents: I work a lot in multi-threaded, heavy-usage environments,

Me too!

However, I expect the synchronization overhead to be mostly  
negligible even in these environments: The synchronization is rather  
short-lived: localized to map.get() and map.put(). These operations  
are very fast, in particular considering that the name and URI  
involved in QName.hashCode() and QName.equals() are typically (but  
not necessarily) String constants, often reducing equality to == and  
hashCode to the String.hashCode cache lookup, both O(1).

In extreme cases where lock contention might indeed become a problem  
one could eliminate all synchronization by putting the cache map into  
a ThreadLocal. But I would recommend not doing that by default. Let's  
first see how the simple approach works...

On Jun 9, 2005, at 10:46 PM, Mik Lernout wrote:

> My 2 cents: I work a lot in multi-threaded, heavy-usage  
> environments, and those synchronized blocks are way to wide and  
> will crush performance when running in ore than one thread.  
> Elliotte: can you add concurrent access in your test cases.
>
> You just need a weak referenced Map as a cache, and use "double  
> checking", or not, as I don't think it is that dangerous that there  
> are two equal QNames floating around of which only one is saved in  
> the cache...

I'm not sure I understand what you mean with "double checking" and  
why weak references would be significantly benefitial.

Wolfgang.