Re: Infinite loop with CountDirective

Should this be fixed in CountDirective.java or in Variable.java?

I haven't studied the code in forever, but if we could change  
Variable.evaluate() to throw a PropertyException whenever val is an  
UndefinedMacro, then it seems like we'd never end up with this sort  
of bug again.

That, or maybe UndefinedMacro.evaluate() should throw?  What value is  
there in trying to evaluate() an UndefinedMacro?

eric

On Mar 28, 2006, at 9:42 AM, Keats Kirsch wrote:

> This certainly looks like a bug.  Thanks for doing such an  
> excellent job of documenting it.  I'll try to commit a patch (and  
> maybe a unit test to go with it) in the next day or so.
>
> I'm pretty sure that the count directive was written before we  
> added the UndefinedMacro, and this edge case was apparently not  
> tested.
>
> Keats
>
> Sven Schliesing wrote:
>
>> Hi,
>>
>> I think I just encountered an infinite loop with the CountDirective.
>>
>> I cut the template down to this snippet to verify the error:
>> #count $i from 1 to $pages {
>> }
>>
>> $pages is not set in the context, so we count from "1 to unknown"
>>
>> In the CountDirective this snippet is responsible for the handling  
>> of the end-value:
>>
>> CountDirective.java
>> -------------
>> 162 if ((tmp = _objEnd) != null)
>> 163        {
>> 164            while (tmp instanceof Macro)
>> 164                tmp = ((Macro) tmp).evaluate(context);
>> ...
>> 173        }
>> -------------
>> I added line numbers for better understanding.
>> Cause _objEnd (and therefore tmp) is a SimplePropertyVariable  
>> (implements Macro), the statement on line 164 gets true and so  
>> evaluate(context) (member of Variable) is called.
>>
>> Variable.java
>> -------------
>> 153 final public Object evaluate (Context context) throws  
>> PropertyException
>> 154    {
>> 155        try
>> 156        {
>> 157            Object val = getValue(context);
>> 158            if (val instanceof Macro)
>> 159            {
>> 160                val = ((Macro) val).evaluate(context); // recurse
>> 161            }
>> 162            return val;
>> 163        }
>> ...
>> ------------
>> getValue(context) on line 157 returns "UndefinedMacro", cause the  
>> value ($pages) is not set. Line 158 evaluates to true, and so  
>> evaluate (context) (member of UndefinedMacro) is called and  
>> returns the class' _singleton (new UndefinedMacro()).
>> So we get back to the beginning in CountDirective. tmp in line 164  
>> gets a new value (singleton of UndefinedMacro).
>> Now we enter the infinite loop: Because UndefinedMacro is a Macro,  
>> too, we call evaluate(context) on it again (line 164) and get  
>> returned: the _singleton of UndefinedMacro. So no change here. tmp  
>> will never change it's value from UndefinedMacro to something  
>> else. It will never ever evaluate to a value that exits our loop.
>>
>> So is it me? Am I getting something totally wrong? An unset end- 
>> variable should result in an error-message, not in an infinite  
>> loop, shouldn't it?
>>
>> Greets,
>>
>> Sven
>>
>
>
>
>
> -------------------------------------------------------
> This SF.Net email is sponsored by xPML, a groundbreaking scripting  
> language
> that extends applications into web and mobile media. Attend the  
> live webcast
> and join the prime developer group breaking into this new coding  
> territory!
> http://sel.as-us.falkag.net/sel? 
> cmd=lnk&kid=110944&bid=241720&dat=121642
> _______________________________________________
> Webmacro-user mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/webmacro-user



-------------------------------------------------------
This SF.Net email is sponsored by xPML, a groundbreaking scripting language
that extends applications into web and mobile media. Attend the live webcast
and join the prime developer group breaking into this new coding territory!
http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642