Re: [PATCH v2] Make xmalloc and xrealloc thread-safe

[Fredrik Kuivinen <frekui@gmail.com>]

On Wed, Apr 7, 2010 at 17:08, Nicolas Pitre <nico@fluxnic.net> wrote:
> On Wed, 7 Apr 2010, Fredrik Kuivinen wrote:
>> diff --git a/thread-utils.c b/thread-utils.c
>> index 4f9c829..3c8d817 100644
>> --- a/thread-utils.c
>> +++ b/thread-utils.c
>> @@ -1,4 +1,5 @@
>>  #include "cache.h"
>> +#include <pthread.h>
>
> This will fail compilation on Windows surely?

I think it will work. We use "#include <pthread.h>" in builtin/grep.c,
builtin/pack-objects.c, and preload-index.c already.

>>  #if defined(hpux) || defined(__hpux) || defined(_hpux)
>>  #  include <sys/pstat.h>
>> @@ -43,3 +44,24 @@ int online_cpus(void)
>>
>>       return 1;
>>  }
>> +
>> +int init_recursive_mutex(pthread_mutex_t *m)
>> +{
>> +#ifdef _WIN32
>> +     /* The mutexes in the WIN32 pthreads emulation layer are
>> +      * recursive, so we don't have to do anything extra here. */
>> +     return pthread_mutex_init(m, NULL);
>> +#else
>> +     pthread_mutexattr_t a;
>> +     int ret;
>> +     if (pthread_mutexattr_init(&a))
>> +             die("pthread_mutexattr_init failed: %s", strerror(errno));
>> +
>> +     if (pthread_mutexattr_settype(&a, PTHREAD_MUTEX_RECURSIVE))
>> +             die("pthread_mutexattr_settype failed: %s", strerror(errno));
>> +
>> +     ret = pthread_mutex_init(m, &a);
>> +     pthread_mutexattr_destroy(&a);
>> +     return ret;
>
> Are you sure the pthread_mutexattr_t object can be destroyed even if the
> mutex is still in use?  Is the attribute object "attached" to the mutex
> or merely used as a template?

It is safe. See
http://www.opengroup.org/onlinepubs/009695399/functions/pthread_mutexattr_init.html

- Fredrik