Re: Sharing read/WRITE data between threads?

I've shared read-only data across threads many times a cheap and easy 
caching mechanims, but as I'm sure you've found in your research, the 
"copy-on-write" methodology employed by mod_perl prevents you from doing 
that for mutable data and I'm not aware of a way around that without 
fundamental changes to mod_perl itself.

There are some very good reasons that mod_perl is architected that way.  
You may very well have a specific use case that makes sharing mutable 
data in memory for a threaded application desirable, but I know that 
oftentimes when I've  tried to find ways to workaround a fundamental 
architectural element in a toolset, the best solution for me has 
ultimately been to rethink my approach rather than to wrestle the 
toolset into submission.

In short, and although this isn't what you asked and I know next to 
nothing about your project, constraints or requirements... it sounds 
like you might want to consider a cache server 
(Redis/Varnish/Elasticache/etc...) and then solve the problem and 
proactively notify subscribed threads of changes if you need to.




On 8/24/2021 7:50 PM, David Booth wrote:
> I am using Apache/2.4.41 (Ubuntu), with mod_perl.  Apache uses 
> multiple threads, and I want to share read/WRITE data between threads. 
> (I.e., I want to be able to modify some shared data in one thread, 
> such that other threads can see those changes.)  In "Practical 
> mod_perl" Stas Bekman describes how to share read-only data between 
> threads, but says nothing about how to share WRITABLE data between 
> threads.
>
> Any clues about how this can be done?  I've searched high and low and 
> found nothing.  I will also want to know what mechanisms are available 
> to coordinate access to that shared data, such as locks or semaphores.
>
> I also posted this message to StackOverflow, but got no response so far:
> https://stackoverflow.com/questions/68901260/how-to-share-read-write-data-in-mod-perl-apache2 
>
>
> Any help would be appreciated!
>
> Thanks,
> David Booth