← Back to team overview

maria-developers team mailing list archive

Re: RFC: Compile-time checking for unmatched DBUG_ENTER/LEAVE via unused variable


Hi, Jeremy!

On Jul 19, Jeremy Cole wrote:
> Prior to posing it as a final patch contribution or opening a JIRA ticket,
> I wanted to propose this idea.
> The attached patch adds what amounts to compile-time checking for unmatched
> variable in DBUG_ENTER which is only used in DBUG_LEAVE. This allows any
> compiler which can robustly detect unused variables to detect the mismatch
> at compile-time. There is already a run-time check for this case, but it is
> somewhat limited as it requires _db_return_ to be called in order to detect
> the mismatch, and this is in practice not always the case. Particularly
> three cases allow this to escape detection:
> 1. Some instrumented functions are called only from non-instrumented
> functions.
> 2. Some instrumented functions are called only from non-returning
> functions, such as abort or die functions.
> 3. Some instrumented functions are called from functions who call my_end
> or my_thread_end (making cs unavailable) before returning.
> In any case please see the attached DRAFT patch for a full implementation
> of the idea. Note one bit of ugliness is that non-returning functions,
> after this patch, must be marked explicitly as DBUG_ENTER_NO_RETURN -- this
> actually is not really a bad thing, though in and of itself.

Thanks, Jeremy!

I kind of liked the idea. Although I, probably, wouldn't use
DBUG_ENTER_NO_RETURN, but a separate macro DBUG_NO_RETURN that would use
your guard variable without calling _db_return_. Hmm, come to think of
it, perhaps functions that don't return should still use DBUG_LEAVE?
Then no special new macro is needed at all.

But what made me thinking was, that this patch only detects whether the
function has at least one DBUG_RETURN, anywhere in the function body
(your changeset comment mentions this, albeit in a wrong place, so it's
a bit confusing). In my experience a notably more popular mistake is to
miss DBUG_RETURN only somewhere in a function, like in the early return
on the error. What could we do to solve this too? Is C++ class the best
we could have?