Re: [PATCH 1/1] bbclass: bb.fatal() clean up

[Robert Yang <liezhi.yang@windriver.com>]

On 05/13/2013 03:24 PM, Mike Looijmans wrote:
> On 05/09/2013 05:34 AM, Robert Yang wrote:
>>
>>
>> On 05/09/2013 10:23 AM, Chris Larson wrote:
>>> On Wed, May 8, 2013 at 7:14 PM, Robert Yang
>>> <liezhi.yang@windriver.com>wrote:
>>>
>>>> On 05/08/2013 08:03 PM, Mike Looijmans wrote:
>>>>
>>>>> On 05/08/2013 11:06 AM, Robert Yang wrote:
>>>>>
>>>>>> The bb.fatal() is defined as:
>>>>>>
>>>>>> def fatal(*args):
>>>>>>       logger.critical(''.join(args))
>>>>>>       sys.exit(1)
>>>>>>
>>>>>> So anything after bb.fatal() in the same code block doesn't have any
>>>>>> effect, e.g.:
>>>>>>
>>>>>>       bb.fatal("%s_%s: %s" % (var, pkg, e))
>>>>>>       raise e
>>>>>>
>>>>>> The "raise e" should be removed.
>>>>>>
>>>>>
>>>>> Just some random thoughts that occurred to me when I read this:
>>>>>
>>>>>
>>>> Hi Mike, thanks for your comments, but the "raise sys.exit(1)" doesn't
>>>> raise
>>>> anything, e.g.:
>>>>
>>>> import sys
>>>>
>>>> def fatal():
>>>>          sys.exit(1)
>>>>
>>>> try:
>>>>          raise fatal()
>>>> except Exception as e:
>>>>          raise e
>>>>
>>>> I think that the "raise fatal()" equals to "fatal()" here.
>>>
>>>
>>> He didn't say raise sys.exit(1), he said sys.exit(1) is equivalent to
>>> raise
>>> SystemExit(1), which it is.
>>>
>>
>> Hi Chris, thanks, if I understand correctly, what you mean is that
>> change the
>> definition of bb.fatal() to let it can raise the exception "e" (not only
>> change
>> the "sys.exit(1)" to "raise SystemExit(1)"), something like:
>>
>> def fatal(e, *args):
>>      logger.critical(''.join(args))
>>      try:
>>      if e:
>>          raise e # if there is e
>>      finally:
>>          # but this one will flush the previous "raise e"
>>          raise SystemExit(1)
>>
>> it seems that this doesn't work (or do we have other ways to make it
>> work that I
>> don't know?) or make much differences.
>>
>> and not all the bb.fatal() has an exception, e.g.:
>>
>> bb.fatal("No OUTSPECFILE")
>>
>> we need change all the current bb.fatal()'s usage, is it worth ?
>>
>> // Robert
>
> I was actually more thinking like this (untested pseusocode follows):
>
> class Fatal(SystemExit):
>      def __init__(self, *args):
>          SystemExit.__init__(self, 1, ''.join(*args)) # or so
>
>
> def fatal(*args):
>      'For backward compatibility'
>      raise Fatal(*args)
>

Hi Mike,

After more investigations, I'm sorry to say that I didn't see many benefits
of this change, the only one that you mentioned we can use "except SystemExit"
to handle the fatal error with the new code, but the "except SystemExit" also
works with the old code, e.g.:

import sys
try:
     sys.exit(1)
except SystemExit:
     print "Catch SystemExit"

And the new code uses:

SystemExit.__init__(self, 1, ''.join(*args))

which can raise more messages, but I think that we need the logger.critical()
here to log the messages in the log file, so we can only use
SystemExit.__init__(self, 1), it seems that it equals to sys.exit(1).

// Robert

>
> New code should use "raise bb.Fatal(..)" instead of "fatal(..)". It has the
> added advantage of being able to explicitly catch and handle the Fatal error.
> Which could be useful in bitbake frontends.
>
> Inheriting from SystemExit makes it behave exactly like the old code in all
> ways, so it wouldn't break things.
>
> It makes it clear what happens. bb.fatal() is a function that doesn't really
> return. But it isn't as fatal as its name suggests, because it really just
> raises an exception, so anyone doing a catch or finally may be surprised by its
> implementation. Converting it into an exception makes it obvious to the world
> what it does without the need for documentation...
>
> Mike.
>
>