Add atomic swap and compare-and-swap

include/vlc_atomic.h

@@ -47,4 +47,7 @@ static inline uintptr_t vlc_atomic_dec (vlc_atomic_t *atom)
     return vlc_atomic_sub (atom, 1);
 }
 
+VLC_EXPORT(uintptr_t, vlc_atomic_swap, (vlc_atomic_t *, uintptr_t));
+VLC_EXPORT(uintptr_t, vlc_atomic_compare_swap, (vlc_atomic_t *, uintptr_t, uintptr_t));
+
 #endif

src/libvlccore.sym

@@ -503,6 +503,8 @@ VLC_Compiler
 vlc_atomic_get
 vlc_atomic_set
 vlc_atomic_add
+vlc_atomic_swap
+vlc_atomic_compare_swap
 vlc_cond_broadcast
 vlc_cond_destroy
 vlc_cond_init

src/misc/atomic.c

@@ -46,6 +46,24 @@ uintptr_t vlc_atomic_add (vlc_atomic_t *atom, uintptr_t v)
     return __sync_add_and_fetch (&atom->u, v);
 }
 
+uintptr_t vlc_atomic_swap (vlc_atomic_t *atom, uintptr_t v)
+{
+    /* grmbl, gcc does not provide an intrinsic for this! */
+    uintptr_t u;
+
+    do
+        u = vlc_atomic_get (atom);
+    while (vlc_atomic_compare_swap (atom, u, v) != u);
+
+    return u;
+}
+
+uintptr_t vlc_atomic_compare_swap (vlc_atomic_t *atom,
+                                   uintptr_t oldval, uintptr_t newval)
+{
+    return __sync_val_compare_and_swap (&atom->u, oldval, newval);
+}
+
 #else
 /* Worst-case fallback implementation with a mutex */
 
@@ -78,4 +96,30 @@ uintptr_t vlc_atomic_add (vlc_atomic_t *atom, uintptr_t v)
     return v;
 }
 
+uintptr_t vlc_atomic_swap (vlc_atomic_t *atom, uintptr_t v)
+{
+    uintptr_t u;
+
+    vlc_mutex_lock (&lock);
+    u = atom->u;
+    atom->u = v;
+    vlc_mutex_unlock (&lock);
+
+    return u;
+}
+
+uintptr_t vlc_atomic_compare_and_swap (vlc_atomic_t *atom,
+                                       uintptr_t oldval, uintptr_t newval)
+{
+    uintptr_t u;
+
+    vlc_mutex_lock (&lock);
+    u = atom->u;
+    if (u == oldval)
+        atom->u = newval;
+    vlc_mutex_unlock (&lock);
+
+    return u;
+}
+
 #endif

src/win32/atomic.c

@@ -50,3 +50,22 @@ uintptr_t vlc_atomic_add (vlc_atomic_t *atom, uintptr_t v)
     return InterlockedExchangeAdd (&atom->s, v) + v;
 #endif
 }
+
+uintptr_t vlc_atomic_swap (vlc_atomic_t *atom, uintptr_t v)
+{
+#if defined (WIN64)
+    return InterlockedExchange64 (&atom->s, v);
+#else
+    return InterlockedExchange (&atom->s, v);
+#endif
+}
+
+uintptr_t vlc_atomic_compare_swap (vlc_atomic_t *atom,
+                                   uintptr_t oldval, uintptr_t newval)
+{
+#if defined (WIN64)
+    return InterlockedCompareExchange64 (&atom->s, newval, oldval);
+#else
+    return InterlockedCompareExchange (&atom->s, newval, oldval);
+#endif
+}