NYCPHP Meetup

[Tim Gales]

Indeed something can always go wrong.

Good error handling should take a page 
out of basic journalism's playbook.

when something goes wrong you want to 
know the five W's --

Who, What, Where, When, and How.

Roughly speaking there are three Where's:

Hardware     (e.g. disk full)
OS or system (e.g. a process never gets
environment   scheduled for some reason -- 
              that is, it doesn't seem to 
              be running for lack of a 
              'time slice')
Software      (this includes utility software 
               like a compiler generating 
               some sort of 'wrong stuff' and
               the developers' logic flaws in
               the application software)

Basically the Who's are determine by what 
mode the code is running in. For example:
kernel mode, user mode etc.

The what's are generally governed by the 
Where's. For instance in unix-like operating 
systems events may be signaled. On a specific 
CPU the hardware may 'trap' to a vector 
interrupt when you try to divide by zero.

In application software (or frameworks as well) 
there will quite likely be a list of possible 
exceptions.

When's are not only the time according to 
the system clock, but also the order in 
which things have happened like a misbehaving 
routine was called just after calling some 
other routine (generally you can get this 
type of information from some sort of 
stack trace).

Putting all the W's together show help 
to come up with an answer for the big 'W' -- 
WHY did something go wrong?

In trying to answer the big W you sometimes
can find yourself sounding like a member on 
a congressional investigation committee.
Saying to yourself things like:
"What did this routine know -- and when did 
he know it".


T. Gales & Associates
'Helping People Connect with Technology'

http://www.tgaconnect.com


> -----Original Message-----
> From: talk-bounces at lists.nyphp.org
> [mailto:talk-bounces at lists.nyphp.org] On Behalf Of Jeff 
> Siegel - PHundamentals
> Sent: Monday, May 10, 2004 7:31 AM
> To: NYPHP Talk
> Subject: [nycphp-talk] NEW PHundamentals Question - Error Handling
> 
> 
> "Something can always go wrong in an application so it is
> essential that 
> your application have an error handler. What types of errors can be 
> safely ignored, and which ones should be trapped by an error handler? 
> What is the best way to handle those errors?"
> 
> Jeff Siegel & Michael Southwell
> The PHundamentals Team
> 
> 
> _______________________________________________
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>