[MPlayer-dev-eng] threaded cache, round 2

[Andrej N. Gritsenko]

    Hello!

Dan Oscarsson has written:
>Attached is a new version of my threaded cache code.

>This version does not have a sleep or timed wait in the cache thread.
>configure need more work, I expect some of you know better then me how
>you want it.

[.......]
>+#ifdef PTHREAD_CACHE
>+    if (!((cache_vars_t *)s->cache_data)->do_work) {
>+        pthread_mutex_lock(&((cache_vars_t *)s->cache_data)->go_ahead_mutex);
>+           ((cache_vars_t *)s->cache_data)->do_work = 1;
>+        pthread_mutex_unlock(&((cache_vars_t *)s->cache_data)->go_ahead_mutex);
>+        pthread_cond_signal(&((cache_vars_t *)s->cache_data)->go_ahead);
>+    } else {
>+        // when cache_do_control loops on the cpu, sometimes system is slow
>+        // to wake up threads. A quick sleep helps
>+        usec_sleep(1);
>+    }
>+#endif
>+
[.......]

    Is it change on do_work possible only in one thread? If not then you
should lock mutex before conditional based on its value. And as soon it's
set to 1 in one thread and to 0 in another (assuming from you code) that
means your code contains race condition, i.e. mutex locking is really not
functional so you have to fix that everywhere.

    With best wishes.
    Andriy.