[Mono-dev] New error handling framework for mono

[Robert Jordan]

Rodrigo Kumpera wrote:
> Finally, it makes up for good consistency to not use the return value as a
> guard for error handling
> because there are cases where returning NULL can mean either a valid
> condition or error.

I did not propose this. The idea was to always return the error
status:

MonoString *str;
int status = mono_string_new_wrapper ("foo", &str);

instead of

MonoString *str = mono_string_new_wrapper ("foo", &error);

Robert


> 
> 
> On Thu, Aug 13, 2009 at 7:28 PM, Robert Jordan <robertj at gmx.net> wrote:
> 
>> Hi,
>>
>> Zoltan Varga wrote:
>>> Hi,
>>>
>>>   I still it would be easier to simply pass a int* or use an int return
>>> value, instead of a structure which needs to be initialized/cleaned up,
>> and
>>> store any excess state in TLS. This is because
>>> most code can't do anything with an error other than cleaning up and
>> passing
>>> it up to the
>>> caller.
>>>
>>> So the code below could look like:
>> I like this.
>>
>>>   err = foo ();
>>>   if (err)
>> Or the same pattern with excess state in TLS:
>>
>> if (foo ())
>>        MonoError *err = mono_get_last_error ();
>>        ...
>>
>> Using the return value to signal an error condition
>> also makes the code more macro-able, e.g.:
>>
>> #define MONO_CHECK(x) do { if ((x))
>>        abort (mono_get_last_error_message ()); } while (0)
>>
>> #define MONO_TRY(x) if ((x)) goto cleanup
>>
>>
>>        MONO_CHECK (foo ());
>>
>> and
>>
>>        MONO_TRY (foo ());
>>        ...
>>
>>        cleanup:
>>
>> Robert
>>
>>
>>>
>>>                                  Zoltan
>>>
>>> On Thu, Aug 13, 2009 at 11:26 PM, Rodrigo Kumpera <kumpera at gmail.com>
>> wrote:
>>>> Hey,
>>>>
>>>> The attached patch implements the basics for the new MonoError struct
>> that
>>>> will be used for error handling in the runtime.
>>>> It has only the basics to support the current exceptions the runtime
>> handle
>>>> for it's operation.
>>>>
>>>> The usage is pretty much like the one in Paolo's email on the subject:
>>>>
>>>> gboolean do_stuff () {
>>>> MonoError error;
>>>> mono_error_init (&error, 0);
>>>> runtime_function_that_might_fail (..., &error)
>>>> if (!mono_error_is_ok (&error))
>>>>   goto fail;
>>>> return TRUE;
>>>>
>>>> fail:
>>>> mono_error_cleaup (&error);
>>>> return FALSE; //or raise an exception using mono_raise_exception
>>>> (mono_error_prepare_exception (&error));
>>>> }
>>>>
>>>> The idea is to replace all error handling code with using this (loader
>>>> error, type exception_data and JIT's exception_type).
>>>>
>>>> Still open is how this would be integrated on 2.6 and if functions
>> should
>>>> error out if passed an already set error object.
>>>> The last point enables more concise code like:
>>>>
>>>> MonoError error;
>>>> MonoType *type = ...;
>>>> mono_error_init (&error);
>>>> MonoClass *class = mono_class_from_mono_type (type, &error);
>>>> mono_class_init (class, &error);
>>>> MonoMethod *method = mono_class_get_method_from_name (class, "Invoke",
>> 1,
>>>> &error);
>>>> if (!mono_error_ok (&error))
>>>>   return NULL;
>>>> return mono_runtime_invoke (method, NULL, params, NULL);
>>>>
>>>> I left behind some aditional features I would like to add to help
>>>> development, like logging, signaling a breakpoint and
>>>> asserting if setting a second error to the same MonoError.
>>>>
>>>> It would be a good time to hear the feeback on everyone about this,
>>>> specially embedders, since this will be the basis for
>>>> error handling of the new API comming in 2.8.
>>>>
>>>> Please comment,
>>>> Rodrigo
>>>>
>>>>
>>>> _______________________________________________
>>>> Mono-devel-list mailing list
>>>> Mono-devel-list at lists.ximian.com
>>>> http://lists.ximian.com/mailman/listinfo/mono-devel-list
>>>>
>>>>
>>>
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>>
> 
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