[Seaside] Error handlers and critical sections

[Ron Teitelbaum]

You are welcome!

- Ron

> -----Original Message-----
> From: C. David Shaffer
> 
> Ron Teitelbaum wrote:
> > Hi David,
> >
> > I'm not sure I really understand your question.  There is a place in the
> > code for handling exceptions.  If you make your own subclass of
> WASession
> > then you can implement something like this:
> >
> > withErrorHandler: aBlock
> > 	"override and extend the basic seaside exception handling"
> >
> > 	^[[super withErrorHandler: [aBlock
> > 		on: USMRSDBObjectRegister do: [:ex | self registerObject: ex
> > object. ex resume]]]
> > 		on: USMRSDBProxyReifier do: [:ex | self getObject: ex
> > object. ex resume]]
> > 		on: USMRSDBCurrentCommitManager do: [:ex | ex resume: self
> > currentCommitManager].
> >
> >
> >
> Yes!  I think that would be better...but with some minor differences.
> All of your handlers jump back into the signaling context (they are more
> like Notifications).  There's no unwinding to be done.  I'm talking
> about dealing with unexpected Errors.  Let me spell out an example:
> 
> MyComponent>>someCallbackMethod
>     model doSomethingImportant
> 
> now in my model
> 
> MyModel>>doSomethingImportant
>     [self useSomeResource. UnexpectedError signal] ensure: [self
> freeSomeResource]
> 
> This ensure: block will never run unless UnexpectedError is handled and
> that handler block exits.  This never happens if you use subclasses of
> WAErrorHandler to deal with errors...hence my unwindTo: attempt.   Your
> example led me to:
> 
> MySession>>withErrorHandler: aBlock
>     ^super withErrorHandler: [aBlock on: Error do: [:ex | MyErrorLogger
> logError: ex].
>             self returnResponse: ...]
> 
> Notice that in order to satisfy the requirement that the resource be
> freed the "self returnResponse:" must be outside the error handler so
> that the ensure: blocks gets invoked.  I think this is much better than
> my previous approach.  Thanks Ron!
> 
> David
> 
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