vlc_global_mutex: common functions for process-wide mutexes

(cherry picked from commit e3c350269cf1b482d2f6842e5b31a83be27a1c40)
(kept core part only to minimize changes)

include/vlc_threads.h

@@ -430,4 +430,12 @@ class vlc_mutex_locker
 };
 #endif
 
+enum {
+   VLC_MAX_MUTEX
+};
+
+VLC_EXPORT( void, vlc_global_mutex, ( unsigned, bool ) );
+#define vlc_global_lock( n ) vlc_global_mutex( n, true )
+#define vlc_global_unlock( n ) vlc_global_mutex( n, false )
+
 #endif /* !_VLC_THREADS_H */

src/libvlccore.sym

@@ -544,6 +544,7 @@ vlc_mutex_init_recursive
 vlc_mutex_lock
 vlc_mutex_trylock
 vlc_mutex_unlock
+vlc_global_mutex
 vlc_object_attach
 vlc_object_create
 vlc_object_find

src/misc/threads.c

@@ -233,3 +233,22 @@ void vlc_thread_cancel (vlc_object_t *obj)
     if (priv->b_thread)
         vlc_cancel (priv->thread_id);
 }
+
+/*** Global locks ***/
+
+void vlc_global_mutex (unsigned n, bool acquire)
+{
+    static vlc_mutex_t locks[] = {
+    };
+    assert (n < (sizeof (locks) / sizeof (locks[0])));
+    vlc_mutex_t *lock = locks + n;
+
+    if (acquire)
+        vlc_mutex_lock (lock);
+    else
+        vlc_mutex_unlock (lock);
+
+    /* Compile-time assertion ;-) */
+    char enough_locks[(sizeof (locks) / sizeof (locks[0])) - VLC_MAX_MUTEX];
+    (void) enough_locks;
+}