Re: Aggressive exception handler making extra work for itself.

On Mon, 2 Apr 2007, Jonathan Swartz wrote:

> For Mason's purposes, we would need to be able to turn on/off stack traces in 
> a dynamically scoped way (e.g. by setting an Exception::Class package var), 
> since we want all errors that occur inside the request to convert to an 
> Exception::Class object, and error_mode can change on a per-request basis.

There's a class data method Trace() that right now is turned on for all 
Mason exceptions. It'd certainly be easy enough to turn that off for abort 
& decline exceptions.

However, there is another problem, which is that Mason catches _all_ 
exceptions and passes them to 
HTML::Mason::Exceptions::rethrow_exception(). This function will turn a 
non-object exception into a HTML::Mason::Exception object, complete with 
stack trace.

This behavior is useful when we're catching a real runtime error in a 
component, because this lets us generate the pretty error pages. However, 
if a component calls code that uses eval blocks internally (as many CPAN 
modules do) then it's a huge waste.

The problem is that there's no way to distinguish between errors we want 
to catch and those we don't. Ideally, every time a piece used an eval 
block it would localize $SIG{__DIE__} in the block or something like that.

So the hacky workaround I came up with was to only set Mason's 
$SIG{__DIE__} handler when the error mode is "output".


-dave

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