threads: add vlc_queuedmutex_held()

include/vlc_threads.h

@@ -578,9 +578,10 @@ VLC_API void vlc_latch_wait(vlc_latch_t *);
 typedef struct {
     atomic_uint head;
     atomic_uint tail;
+    atomic_ulong owner;
 } vlc_queuedmutex_t;
 
-#define VLC_STATIC_QUEUEDMUTEX { ATOMIC_VAR_INIT(0), ATOMIC_VAR_INIT(0) }
+#define VLC_STATIC_QUEUEDMUTEX { ATOMIC_VAR_INIT(0), ATOMIC_VAR_INIT(0), ATOMIC_VAR_INIT(0) }
 
 void vlc_queuedmutex_init(vlc_queuedmutex_t *m);
 
@@ -588,6 +589,22 @@ void vlc_queuedmutex_lock(vlc_queuedmutex_t *m);
 
 void vlc_queuedmutex_unlock(vlc_queuedmutex_t *m);
 
+/**
+ * Checks if a queued mutex is locked.
+ *
+ * This function checks if the calling thread holds a given queued mutual
+ * exclusion lock. It has no side effects and is essentially intended for
+ * run-time debugging.
+ *
+ * @note To assert that the calling thread holds a lock, the helper macro
+ * vlc_queuedmutex_assert() should be used instead of this function.
+ *
+ * @retval false the mutex is not locked by the calling thread
+ * @retval true the mutex is locked by the calling thread
+ */
+bool vlc_queuedmutex_held(vlc_queuedmutex_t *m);
+
+#define vlc_queuedmutex_assert(m) assert(vlc_queuedmutex_held(m))
 /**
  * One-time initialization.
  *

src/misc/threads.c

@@ -467,6 +467,12 @@ void vlc_queuedmutex_init(vlc_queuedmutex_t *m)
 {
     atomic_init(&m->head, 0);
     atomic_init(&m->tail, 0);
+    atomic_init(&m->owner, 0);
+}
+
+bool vlc_queuedmutex_held(vlc_queuedmutex_t *m)
+{
+    return (vlc_thread_id() == atomic_load_explicit(&m->owner, memory_order_relaxed));
 }
 
 void vlc_queuedmutex_lock(vlc_queuedmutex_t *m)
@@ -478,10 +484,13 @@ void vlc_queuedmutex_lock(vlc_queuedmutex_t *m)
     while ((head = atomic_load_explicit(&m->head,
                                         memory_order_acquire)) != ticket)
         vlc_atomic_wait(&m->head, head);
+
+    atomic_store_explicit(&m->owner, vlc_thread_id(), memory_order_relaxed);
 }
 
 void vlc_queuedmutex_unlock(vlc_queuedmutex_t *m)
 {
+    atomic_store_explicit(&m->owner, 0, memory_order_relaxed);
     atomic_fetch_add_explicit(&m->head, 1, memory_order_release);
     vlc_atomic_notify_all(&m->head);
 }