Re: [Jelly] nested compileScript() with import ?

[Arnaud Masson]

Hans Gilde wrote:
Maybe it's getLastModified instead of getDate?
 

yes, it works much better!
You probably know, but there's another performance characteristic of my
solution: the Servlet threads only contend for a lock during the time it
takes to look the Script up from the Map. With yours, the threads have a
much larger window for contention. This would only make a difference if your
application will run many instances in many threads.
 

I agree.
(in my case the number of concurrent connections is small)
What about an application variable "flushJellyCache"? At the beginning of
the Servlet, check for that variable. If it's true, lock the application,
remove all from the Map, set to false. Now you can flush the cache by hand
from the web interface or a management client.
 

Now that I can get the date of the script files, I can implement an 
automatic flushing and manage the global cache that you describe,
so my per-session cache solution isn't useful anymore.
That's what occurs in JSP, when you edit a .jsp page, it is recompiled 
transparently.

Thanks.
With your help, there is now no advantage left for JSP compared to jelly.
Hans
-----Original Message-----
From: Arnaud Masson [mailto:[EMAIL PROTECTED] 
Sent: Monday, December 06, 2004 12:11 PM
To: Jakarta Commons Users List
Subject: Re: [Jelly] nested compileScript() with import ?

Hans Gilde wrote:
 

Arnaud,
You're right about how JSP works; maybe you could file an issue about this
in Jelly's jira? This seems like something that many web users would want.

   

done (sorry for the double post #170/171, the server wasn't responding)
 

Sorry to introduce problems but...
To get the benefit of your solution, you will need to reuse the cache
between Servlet invocations. The basic Jelly Servlet does not reuse the
JellyContext between invocations. Here's the pain: the context isn't
entirely thread safe (actually, the parser isn't thread safe and the
   

context
 

uses a single parser).
Here's what you can do:
Set the HashMap into the context before invoking the script. If inherit is
true (by default), the Map will be accessible throughout your entire
   

script.
 

Now that your Servlet has a handle on the HashMap, you can keep it in an
instance variable (must be a thread safe HashMap) or as an application
variable or whatever.

   

Currently I put the JellyContext (including the script cache) in the web 
session.
When I use this JellyContext , I do a synchronized(myContext) {...} to 
avoid the threading problem.
Of course the cache isn't shared across session.

Your solution is better but the per-session solution has one advantage.
You can easily purge the cache when you open a new session, which is 
useful when you modify the jelly scripts.
I have tried to use URLConnection.getDate() to discard the cache,
but it doesn't work on the jndi URL provided by tomcat with 
ServletContext.getResource(), it always returns 0.
Any idea how I can manage cache update ?

 

-----Original Message-----
From: Arnaud Masson [mailto:[EMAIL PROTECTED] 
Sent: Monday, December 06, 2004 4:06 AM
To: Jakarta Commons Users List
Subject: Re: [Jelly] nested compileScript() with import ?

Hans Gilde wrote:

   

Ok, it sounds reasonable to want those caching conditions. But for my own
curiosity, why do you want them? Are you in a tight memory situation or is
it a perfectionist thing?

  

     

It's for speed, especially for Script.run().
I must run many small scripts to build page, so I would like to minimize 
IO and XML parsing.
The outputs of the scripts are assembled in a big DOM,
under the control of a java loop which also makes some modifications to 
the DOM.
(I use a custom ContentHandler so that jelly output is directly added in 
the document without parsing.)

I think that in a classic JSP, all included pages are compiled when the 
main jsp  is compiled,
so there is no performance penalty there. I would like the same thing in 
jelly.


   

What's wrong with using JellyContext variables? It's pretty much what
they're there for.

  

     

I had the idea that the cached scripts were technical details and should 
not be at the same level as user variables.
This time, it's probably a "perfectionist thing" ! :-)


   

You can think of a JellyContext as a scope. At each level of XML tag, you
get a new JellyContext (a new scope). Export says "when a variable is set
into the current scope, should I automatically put it into the scope
  

     

above"?
   

Inherit says "when creating a new scope, should I give it all the
     

variables
 

  

     

from the current scope"?

   

If a Tag wants to set a variable in a context (scope) that's higher up in
the tree, there are two choices: use export=true or find the parent
     

context
 

(while ((parent = getParent()) != null)).
To find a variable that's been set into a context above yours, either use
inherit=true or findVariable.
I'd suggest this solution:
Have your Tag find the top level context (while ((parent = getParent()) !=
null)). Use a single variable name in this context, say
  

     

my_imported_scripts.
   

That variable will be a single HashMap from uri to parsed Script instance.
  

     

Ok, I'm going to try this.

   

As you saw, compilable tags are sort of compiled, but they don't get a
context or their attributes at that point. The problem with compilable
     

tags
 

(I don't recommend using them) is that they're only compiled with respect
  

     

to
   

the thread that compiles them. If you run the same Script in a different
thread, those compiled tags won't be there. This is not true for a Script.
Once a Script is compiled, it stays compiled no matter where you use it.

  

     

I don't think I need the advanced Script based solution for now, the 
cache map must be sufficient for me.

Thanks for your help.

   

Hans
-----Original Message-----
From: Arnaud Masson [mailto:[EMAIL PROTECTED] 
Sent: Sunday, December 05, 2004 5:06 PM
To: Jakarta Commons Users List
Subject: Re: [Jelly] nested compileScript() with import ?

Yes,  I have copied the import tag and added the cache to the new tag.
It works fine, but I would like to reuse compiled scripts
- if several container scripts include the same sub script
- if a container script include the same sub script several times
To do that, I currently use the JellyContext to cache compiled scripts 
with a call to setVariable(),
using a variable name based on the script uri... it works, but it's not 
really clean.

Maybe a better way would be to override the compileScript() methods of 
the JellyContext
and add a cache of compiled scripts inside the context (indexed by 
uri/url) ?

Also I am not sure how to handle the 'export' and 'inherit' parameters 
when I use compileScript+run instead of a single call to runScript().

You say a Tag isn't compilable, but what's the "CompilableTag" ??
I tried to use it the but the attributes (uri,...) of my tag are empty 
when "compile" is called.

Thanks for your help!

.Hans Gilde wrote:

  

     

You could easily cache the imported script the first time it's run. This
    

       

is
   

a simple modification to the current import tag, so that it keeps the
reference to the script. If you do this, why not add an attribute "cache"
 

    

       

to
  

     

turn caching on/off and then submit it as a patch to the import tag?
It would be a little harder, but not at all impossible, to make it cache
 

    

       

the
  

     

imported script at compile time.
If not, the basic idea is this:
A Tag isn't compilable, it's generated at runtime. A Script is
       

compilable,
 

it's generated at compile time. You need a special Script, not a special
Tag. Scripts are very much like tags except that they need to be thread
safe. Most of the time, a Script called TagScript is used. By default,
    

       

this
   

Script creates and caches Tag instances when it's run.
Your new Script would compile the import at compile time. The result of
compiling the import is, it self, a Script instance. At runtime, your
 

    

       

Script
  

     

would simply pass control to the imported Script.
You would also have to implement a custom TagLibrary. A TagLibrary gets
       

to
 

create a TagScript (implements Script) for every XML tag in its
       

namespace.
 

So, your TagLibrary would create a custom TagScript that would compile
       

and
 

keep the imported XML.
-----Original Message-----
From: Arnaud Masson [mailto:[EMAIL PROTECTED] 
Sent: Saturday, December 04, 2004 6:07 PM
To: [EMAIL PROTECTED]
Subject: [Jelly] nested compileScript() with import ?

hi
in the current version of jelly "import" tag, it seems that imported 
scripts are always parsed and recompiled each time the containing script 
runs,
even if this script has already been compiled.

the problem is that  it isn't optimized if the compiled version of the 
main script is cached.

is it possible to compile all scripts included via <j:import ...> via a 
single call to jellyContext.compileScript() on the containing script ?
should i write a custom tag to implement that (to replace import) ?

thanks in advance
arnaud

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