Re: concurrency problem with #include as template

My theory is that SimpleCacheManager.java is broken (http:// 
cvs.sourceforge.net/viewcvs.py/webmacro/webmacro/src/org/webmacro/ 
resource/SimpleCacheManager.java?rev=1.2&view=markup)

It seems the get(query, helper) function would allow concurrent  
readers to load and put the same resource in the _cache at the same  
time.  Obviously, in the end we'd only have one entry in the map, but  
we'd be loading the template twice.

But I don't see how this explains getting the *wrong* template back.   
I would think that concurrent.jar's ConcurrentHashMap would have to  
be broken in order for this to happen.

Just a theory tho.  I've never run across this myself.  Maybe Brian  
can chime in?

Also, a note to Carl.  I realize your wmtest.jar file is designed to  
expose this bug, but if your real code is creating new WM instances  
for *every* thread, you should consider not doing that.  Instead,  
keep one global WM instance.  Just make sure to give each thread  
their own Context object via _wm.getContext().  When WM is working  
properly, a separate Context per thread is all that's needed to  
guarantee thread-safety.

eric

On Feb 4, 2006, at 4:09 PM, Marc Palmer wrote:

>
> On 4 Feb 2006, at 18:56, Carl H. Sayres wrote:
>
>> Hello,
>>
>> We've encountered a concurrency problem with the #include as  
>> template directive. It appears that when multiple threads of  
>> execution are running, webmacro can intermittently select a  
>> different template than the one requested. We have created a test  
>> program that demonstrates the problem. If anyone can provide  
>> insight into the cause of the problem, (or even better, a fix), we  
>> would be very appreciative.
>
> Thanks for this Carl. I haven't had time to run the test but I've  
> looked at the source of it.
>
> It definitely looks like you've found some obscure problem, but  
> it's possible it is either in the include mechanism, template cache  
> implementation, or the introspection code.
>
> Anybody got time to look at this?
>
> cheers
>
>
>
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