Request for review (S): JDK-8011009: Use do-while(0) instead of while(0) in EC_TRACE and RC_TRACE* macros

[Mikael Vidstedt]

Good point, thanks for clarifying..

/Mikael - macro hater

On 3/28/2013 4:22 PM, Krystal Mo wrote:
> Hi Mikael,
>
> I'd say it has to do with the way ResourceMark works.
>
> Dummy example:
>
> void foo(Symbol* sym) {
>   RC_TRACE(("%s", sym->as_C_string())); // as_C_string allocates resource
> }
>
> ideally this should get expanded into:
>
> void foo(Symbol* sym) {
>   if (RC_TRACE_ENABLED(some_level)) {
>     ResourceMark rm; // note here
>     tty->print("RedefineClasses-0x%x: ", level);
>     tty->print("%s", sym->as_C_string()); // resource allocation in 
> the same scope as the ResourceMark
>   }
> }
>
> If RC_TRACE were made into a (inline) function, then the ResourceMark 
> will have to be taken care of by the caller, like so:
>
> void foo(Symbol* sym) {
>   ResourceMark rm;
>   RC_TRACE(("%s", sym->as_C_string())); // as_C_string allocates resource
> }
>
> Otherwise we'd leak resource-allocated memory. This is the only reason 
> I can think of for keeping it as a macro instead of turning it into a 
> real function.
>
> - Kris
>
> On 03/28/2013 04:12 PM, Mikael Vidstedt wrote:
>>
>> I'm curious: Are there any fundamental reasons for not turning these 
>> into real functions instead of using macros to avoid the problem all 
>> together? The only downside I can see is that the functions would to 
>> do a va_start/va_end and use the va_list version of print instead, 
>> but that doesn't seem all to bad?
>>
>> Cheers,
>> Mikael
>>
>> On 2013-03-28 15:11, Krystal Mo wrote:
>>> Hi all,
>>>
>>> Could I have a review for this small patch, please?
>>>
>>> Webrev: http://cr.openjdk.java.net/~kmo/8011009/webrev.00
>>> CR: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8011009
>>>
>>> This patch improves the EC_TRACE and RC_TRACE* family of macros to 
>>> be less error prone.
>>> They used to end with while(0) to make the macros statement-like, 
>>> but a better way to do this is do {...} while(0).
>>>
>>> Testing with JPRT, will send an update email when it's done.
>>>
>>> P.S. I'm not sure where I should send this email for review, should 
>>> it be hotspot-runtime or serviceability?
>>>
>>> Thanks,
>>> Kris
>>
>