[phobos] Calling abort() on unhandled exception

[Andrei Alexandrescu]

Sean Kelly wrote:
> On Jul 29, 2010, at 9:37 PM, Andrei Alexandrescu wrote:
> 
>> Sean Kelly wrote:
>>> On Jul 29, 2010, at 8:21 PM, Walter Bright wrote:
>>>> Andrei Alexandrescu wrote:
>>>>> Walter Bright wrote:
>>>>>> I think we misunderstand each other. A file copy program 
>>>>>> that fails due to, say, the disk being full, should not 
>>>>>> produce a core dump. It should produce an error message 
>>>>>> like:
>>>>>> 
>>>>>> error: disk full
>>>>>> 
>>>>>> An uncaught exception is NOT an invalid or crashed program
>>>>>>  in D.
>>>>> I think Sean talks about Throwable objects that are not 
>>>>> Exception objects.
>>>>> 
>>>> It's reasonable for seg fault exceptions to produce a core 
>>>> dump. It isn't for recoverable Exceptions, or for 
>>>> non-recoverable ones like out of memory.
>>> At the moment, we don't differentiate between seg faults and 
>>> non-recoverable errors.  Though seg faults are only thrown as 
>>> exceptions on Windows which doesn't have core dumps anyway, as 
>>> far as I know. For what it's worth, I was investigating this bug:
>>>  http://d.puremagic.com/issues/show_bug.cgi?id=4385
>> I see. Overall, my opinion is that regular exceptions that escape 
>> main(0 should simply print their error message to stderr and 
>> exit(1). There should be no stack trace, abort(), core dump, or 
>> anything worse than that. Print the string and exit(1). Anything 
>> more will force most people to actually insert a try/catch in main
>>  to do the simple thing.
> 
> I think the stack trace at least should remain. People have been 
> begging for that for years, and I do think it's pretty useful. Simply
> printing an error message says nothing about the context, and it's
> context that gives error messages meaning.

I for one really enjoy stuff like:

void main(string[] args)
{
     enforce(args.length > 1, "Usage: prog arg");
     ...
}

Having a stack trace tacked there... not good. Exception messages are 
meant to be seen by users. Stack traces are meant to be seen by the 
programmer. The fact that we print both by default doesn't sit well at all.

> As for core dumps, if the user wants them for unhandled exceptions 
> rather than just segfaults, there's currently no way to get them with
>  a D app because main() catches everything.

Well we need to do something about that.

> I'm not sure about the 
> merit of failing via abort() vs. returning -1, but I do think it's a
>  nice option to have available.  Personally... I dunno.  I'd mostly 
> want them for segfaults and bus errors, and I can do that with signal
>  handlers.  I'd have to defer to someone else on that. 

Is it reasonable to say that Exception is the "nicer" thing and 
Throwable is the "less nice" thing that is handled differently? Then 
come bus errors, which are "not nice at all".


Andrei