Re: Clarification for approaches around exception handling

SF Markus Elfring
2017-10-25T06:35:19Z

> But anyways I guess other people sometimes disagree with me.

Am I one of them? ;-)

> Unwinding is for when you allocate five things in a row.

This is a general issue.

I find that it is also needed in this function as usual.

> You have to undo four if the last allocation fails.

Concrete numbers might help to clarify another example.

> But say you have to take a lock part way through and drop it before
> the end of the function. The lock/unlock is not part of the list
> of five resources that you want the function to take so it doesn't
> belong in the unwind code.

Such a view is useful to some degree.

> If you add the lock/unlock to the unwind code, then it makes things a
> bit tricky because then you have to do funny things like:
>
> free_four:
> free(four);
> goto free_three: <-- little bunny hop
> unlock: <-- less useful label
> unlock();
> free_three:
> free_three();
> free_two:
> free(two);
> free_one:
> free(one);
>
> return ret;
>
> It's better to just do the unlocking before the goto.

I would prefer to store such an action also only so often in the code
as it is really required.

> That way the lock and unlock are close together.

It might look nice occasionally.

> if (!four) {
> unlock();
> ret = -EFAIL;
> goto free_three;
> }
>
> Of course, having a big unlock label makes sense if you take a lock at
> the start of the function and need to drop it at the end. But in this
> case we are taking a lock then dropping it, and taking the next, then
> dropping it and so on. It's a different situation.

Lock scopes can interfere with a preferred control flow, can't they?

I have got the impression that your detailed reply could have been
more appropriate for update suggestions around other software modules.

Regards,
Markus