2010/7/27 Denis Kudriashov
<dionisiydk@gmail.com>
Hello,
I found method doesNotUnderstand have very strange implementation
Object>>doesNotUnderstand: aMessage
� ��� | exception resumeValue |
��� (exception := MessageNotUnderstood new)
��� ��� message: aMessage;
��� ��� receiver: self.
��� resumeValue := exception signal.
��� ^exception reachedDefaultHandler
��� ��� ifTrue: [aMessage sentTo: self]
��� ��� ifFalse: [resumeValue]
When Error has no handlers #defaultAction is executed. For MessageNotUnderstood #defaultAction is UnhandledError signal. And for UnhandledError #defaultAction is opening debugger.
If you change it to do nothing (^self) you get infinite loop on any MessageNotUnderstood signal.
It is because "ifTrue" branch executed in doesNotUnderstood method and message resend to receiver.
Why method implemented such way? Why it is differ from ProtoObject implementation. I think It's bug implementation.
This is intentional. �Martin's reply is one half of the issue, that you want to be able to proceed after defining a method in �the debugger. �The otehr half is that you want to be able to catch doesNotUnderstand: in an exception handler and proceed with a result, e.g.
[nil zork]
on: MessageNotUnderstood
do: [:ex|
ex message selector == #zork ifTrue:
[ex resume: #ok].
ex pass]
evaluates to #ok.
�
I found this problem when I try implement stuff to turn off openning debugger on unhandled error (and write it to log)
UnhandledError>>defaultAction
��� "The current computation is terminated. The cause of the error
should be logged or reported to the user. If the program is operating in
an interactive debugging environment the computation should be
suspended and the debugger activated."
��� ^ToolSet debugError: exception.
ToolSet class>>debugError: anError
��� "Handle an otherwise unhandled error"
��� self default ifNil:[ | ctx |
��� ��� Smalltalk
��� ��� ��� logError: anError description
��� ��� ��� inContext: (ctx := anError signalerContext)
��� ��� ��� to: 'PharoDebug.log'.
��� ��� self inform: (anError description, String cr, ctx shortStack).
��� ��� ^anError return].
��� ^self default debugError: anError
I just implement subclass of StandartToolSet with empty method #debugError:. Then I do "ToolSet default: MyToolSet". And now unhandled errors raise infinit loop and never return.
I fix that by:
MyToolSet>>debugError: anError
�� anError class = MessageNotUnderstand ifTrue: [anError reachedDefaultHandler: true].
I think this is hack. But it is work. No errors show to user.And all work good.
What do you think?
I think that the bug is that you haven't modified the system to quit on an UnhandledException. �i.e. in a headless context control should never get back to the doesNotUnderstand: method if the MessageNotUnderstood exception is not caught. �How should one continue after an unhandled error?
HTH
Eliot
Best regards,
Denis
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