Re: Deadlock issue

Thursday, April 19, 2012, 12:32:19 PM, Jacopo Cappellato wrote:

> On Apr 19, 2012, at 11:45 AM, Daniel Dekany wrote:
>
>> Then maybe you share the same
>> freemarker.jar file (same full-path) for multiple applications, and
>> are also using the deprecated default shared (static) ObjectWrapper
>> instance (or some other ObjectWrapper instance which is somehow shared
>> between applications). 
>
> I think you are hitting the point Daniel; here is the OFBiz
> framework code that performs the setup of the wrapper and freemarker
> configuration; the same is then used by all webapplications to render templates:
>
>     protected static BeansWrapper defaultOfbizWrapper =
> BeansWrapper.getDefaultInstance();

Here, you should have `new BeansWrapper()`, assuming this runs once per
webapp. Then the webapps will not share the introspection cache.

Now, maybe the OFBiz developers wanted the application to share the
introspection cache for lower total RAM usage. However doing so also
means more blocking (because access to the cache in synchronized),
which I'm not sure how that affects you. But of course the main
problem here is the frequent cache flushing... One would think that
adding an option for disabling reloading-detection would be
sufficient, since BeansWrapper's introspection cache looks up classes
by identity, not by name (so it could handle multiple versions of the
same class). But the cache of ClassBasedModelFactory (used for statics
and enums) uses the class name (a String) as the key, so... for now,
the best would be just using `new BeansWrapper()`. (However, it should
be checked if OFBiz uses BeansWrapper.getDefaultInstance() somewhere
else too... certainly not, but better check it.)

I'm also surprised on the kind of wrapper used here. Most frameworks
should just use `new DefaultObjectWrapper()`, or `bw = new
BeansWrapper(); bw.setSimpleMapWrapper(true);`. However, to be honest,
this is messy part of FreeMarker (which wrapper to use and why), so
I'm not blaming the OFBiz developers. Do you access map items as
`someMap.get(theKey)` in templates under OFBiz?

>     protected static Configuration defaultOfbizConfig =
> makeConfiguration(defaultOfbizWrapper);
>
>     public static Configuration makeConfiguration(BeansWrapper wrapper) {
>         Configuration newConfig = new Configuration();
>         newConfig.setObjectWrapper(wrapper);
>         newConfig.setSharedVariable("Static", wrapper.getStaticModels());
>         newConfig.setLocalizedLookup(false);
>         newConfig.setTemplateLoader(new FlexibleTemplateLoader());
>        
> newConfig.setAutoImports(UtilProperties.getProperties("freemarkerImports"));
>         newConfig.setTemplateExceptionHandler(new
> FreeMarkerWorker.OFBizTemplateExceptionHandler());
>         // Transforms properties file set up as key=transform name, property=transform class name
>         ClassLoader loader =
> Thread.currentThread().getContextClassLoader();
>         Enumeration<URL> resources;
>         try {
>             resources =
> loader.getResources("freemarkerTransforms.properties");
>         } catch (IOException e) {
>             Debug.logError(e, "Could not load list of
> freemarkerTransforms.properties", module);
>             throw UtilMisc.initCause(new
> InternalError(e.getMessage()), e);
>         }
>         while (resources.hasMoreElements()) {
>             URL propertyURL = resources.nextElement();
>             Debug.logInfo("loading properties: " + propertyURL, module);
>             Properties props =
> UtilProperties.getProperties(propertyURL);
>             if (props == null || props.isEmpty()) {
>                 Debug.logError("Unable to locate properties file " + propertyURL, module);
>             } else {
>                 loadTransforms(loader, props, newConfig);
>             }
>         }
>
>         return newConfig;
>     }
>
>
> and in the same class we use this static method to render the template:
>
>     public static Environment renderTemplate(Template template,
> Map<String, Object> context, Appendable outWriter) throws TemplateException, IOException {
>         // make sure there is no "null" string in there as FreeMarker will try to use it
>         context.remove("null");
>         // Since the template cache keeps a single instance of a
> Template that is shared among users,
>         // and since that Template instance is immutable, we need
> to create an Environment instance and
>         // use it to process the template with the user's settings.
>         Environment env =
> template.createProcessingEnvironment(context, (Writer) outWriter); 
> // NOTE: this is where the process blocks in a deadlock
>         applyUserSettings(env, context);
>         env.process();   // NOTE: this is where the process blocks in a deadlock
>         return env;
>     }
>
> Jacopo

-- 
Best regards,
 Daniel Dekany


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