Re: [PATCH] nptl: Avoid using PTHREAD_MUTEX_DEFAULT in macro definition [BZ #25271]

[Florian Weimer <fweimer at redhat dot com>]

* Adhemerval Zanella:

> On 27/01/2020 10:53, Florian Weimer wrote:
>> Commit 1c3f9acf1f1f75faa7a28bf39af64afd ("nptl: Add struct_mutex.h")
>> replaced a zero constant with the identifier PTHREAD_MUTEX_DEFAULT
>> in the macro PTHREAD_MUTEX_INITIALIZER.  However, that constant
>> is not available in ISO C11 mode:
>> 
>> In file included from /usr/include/bits/thread-shared-types.h:74,
>>                  from /usr/include/bits/pthreadtypes.h:23,
>>                  from /usr/include/pthread.h:26,
>>                  from bug25271.c:1:
>> bug25271.c:3:21: error: ‘PTHREAD_MUTEX_DEFAULT’ undeclared here (not in a function)
>>     3 | pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
>>       |                     ^~~~~~~~~~~~~~~~~~~~~~~~~
>> 
>> This commit change the constant to the equivalent
>> PTHREAD_MUTEX_TIMED_NP, which is in the POSIX extension namespace
>> and thus always available.
>> 
>> Tested on x86_64-linux-gnu and i686-linux-gnu.  Verified that a
>> minimal example now builds in -std=c11 mode.
>
> LGTM, although I think we should add some more extensive tests when
> 2.32 opens.

Thanks.  Siddhesh, should we still put this into the release, or
backport it afterwards?

>> -----
>>  sysdeps/nptl/pthread.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/sysdeps/nptl/pthread.h b/sysdeps/nptl/pthread.h
>> index 7825737840..44dd707896 100644
>> --- a/sysdeps/nptl/pthread.h
>> +++ b/sysdeps/nptl/pthread.h
>> @@ -84,7 +84,7 @@ enum
>>  
>>  
>>  #define PTHREAD_MUTEX_INITIALIZER \
>> - { {  __PTHREAD_MUTEX_INITIALIZER (PTHREAD_MUTEX_DEFAULT) } }
>> + { {  __PTHREAD_MUTEX_INITIALIZER (PTHREAD_MUTEX_TIMED_NP) } }
>
> Maybe add a comment stating why PTHREAD_MUTEX_TIMED_NP is the correct
> initializer here?

I don't want to add internal documentation to installed header files, in
case an application programmer reads them.

Thanks,
Florian