Re: [PATCH 27/36] attr: convert to new threadsafe API

> On Wed, Oct 26, 2016 at 11:35:58AM +0200, Simon Ruderich wrote:
>
>> >  static pthread_mutex_t attr_mutex;
>> > -#define attr_lock()pthread_mutex_lock(&attr_mutex)
>> > +static inline void attr_lock(void)
>> > +{
>> > +   static int initialized;
>> > +
>> > +   if (!initialized) {
>> > +           pthread_mutex_init(&attr_mutex, NULL);
>> > +           initialized = 1;
>> > +   }
>> > +   pthread_mutex_lock(&attr_mutex);
>> > +}
>>
>> This may initialize the mutex multiple times during the first
>> lock (which may happen in parallel).
>>
>> pthread provides static initializers. To quote the man page:
>>
>>     Variables of type pthread_mutex_t can also be initialized
>>     statically, using the constants PTHREAD_MUTEX_INITIALIZER
>>     (for fast mutexes), PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP
>>     (for recursive mutexes), and
>>     PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP (for error checking
>>     mutexes).
>
> I seem to recall this does not work on Windows, where the pthread
> functions are thin wrappers over CRITICAL_SECTION. Other threaded code
> in git does an explicit setup step before entering threaded sections.
> E.g., see start_threads() in builtin/grep.c.
>