Re: Why is FlowInterpreter SingleThreaded?

[Christopher Oliver]

Again I know nothing about Avalon, but there seems to be some conceptual 
confusion between "Stateless" and "ThreadSafe". Stateless objects are of 
course thread-safe but stateful objects may be also. A container that 
automatically turns a "ThreadSafe" component into a singleton seems 
broken to me. Rather I would have thought that a container would provide 
synchronization to such components.

My $0.02,

Chris

Sylvain Wallez wrote:

Carsten Ziegeler wrote:

Christopher Oliver wrote:
 

I think "SingleThreaded" is rather misleading in this case.  I know 
nothing about Avalon but from my experience it appears one flow 
interpreter is created per sitemap. However, this instance is 
definitely accessed by many threads concurrently. I had to put my 
own synchronization code into FOM_JavaScriptInterpereter to handle 
this.

  
Yes, each sitemap holds a reference to the interpreter. As the sitemaps
are ThreadSafe (one single instance per sitemap), this is true
for the actual use of the interpreter as well.
Now, if I understand you correctly, the interpreter can handle multiple
requests at the same time? So, if this is true, it's ThreadSafe
and we should change it.
After looking carefully, the interpreter must be SingleThreaded, even 
if thread safe...

This is because although an intepreter can handle concurrent requests, 
each sitemap must have a different instance, since the interpreter 
holds the scripts defined in a <map:flow> statement.

So if the interpreter is made ThreadSafe, a unique instance will exist 
for the whole system, and will mix all script definitions and script 
global variables. Making it SingleThreaded ensures each sitemap will 
have its own instance. It seems hacky, but I don't see what other 
means we have to achieve this...

Sylvain