[FFmpeg-devel] [PATCH] avcodec/utils: use a default lock manager that uses a pthread mutex

[wm4]

On Fri, 18 Oct 2013 21:04:47 +0200
Michael Niedermayer <michaelni at gmx.at> wrote:

> That makes avformat & avcodec thread safe without the need to explicitly
> register a lock manager.
> 
> Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> ---
>  libavcodec/utils.c |   50 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 49 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/utils.c b/libavcodec/utils.c
> index 3832b81..735c8e0 100644
> --- a/libavcodec/utils.c
> +++ b/libavcodec/utils.c
> @@ -56,9 +56,57 @@
>  # include <iconv.h>
>  #endif
>  
> +#if HAVE_PTHREADS
> +#include <pthread.h>
> +static int default_lockmgr_cb(void **arg, enum AVLockOp op)
> +{
> +    void * volatile * mutex = arg;
> +    int err;
> +
> +    switch (op) {
> +    case AV_LOCK_CREATE:
> +        return 0;
> +    case AV_LOCK_OBTAIN:
> +        if (!*mutex) {
> +            pthread_mutex_t *tmp = av_malloc(sizeof(pthread_mutex_t));
> +            if (!tmp)
> +                return AVERROR(ENOMEM);
> +            if ((err = pthread_mutex_init(tmp, NULL))) {
> +                av_free(tmp);
> +                return AVERROR(err);
> +            }
> +            if (avpriv_atomic_ptr_cas(mutex, NULL, tmp)) {
> +                pthread_mutex_destroy(tmp);
> +                av_free(tmp);
> +            }
> +        }
> +
> +        if ((err = pthread_mutex_lock(*mutex)))
> +            return AVERROR(err);
> +
> +        return 0;
> +    case AV_LOCK_RELEASE:
> +        if ((err = pthread_mutex_unlock(*mutex)))
> +            return AVERROR(err);
> +
> +        return 0;
> +    case AV_LOCK_DESTROY:
> +        if (*mutex)
> +            pthread_mutex_destroy(*mutex);
> +        av_free(*mutex);
> +        avpriv_atomic_ptr_cas(mutex, *mutex, NULL);
> +        return 0;
> +    }
> +    return 1;
> +}
> +static int (*lockmgr_cb)(void **mutex, enum AVLockOp op) = default_lockmgr_cb;
> +#else
> +static int (*lockmgr_cb)(void **mutex, enum AVLockOp op) = NULL;
> +#endif
> +
> +
>  volatile int ff_avcodec_locked;
>  static int volatile entangled_thread_counter = 0;
> -static int (*lockmgr_cb)(void **mutex, enum AVLockOp op);
>  static void *codec_mutex;
>  static void *avformat_mutex;
>  

Looks much better, but doesn't seem to use the internal pthread
emulation if required (on win32, os/2). So it would be "safe" on Unix
only.