atomic: Separate bool and old-value compare-and-exchange

Some implementations only offer one version of compare-and-exchange,
thus we expose both through cairo-atomic, implementing what is missing
through appropriate fallbacks.
*_cmpxchg() now return a boolean (this unbreaks _cairo_atomic_uint_cmpxchg)
*_cmpxchg_return_old() return the old value
Code is updated everywhere to reflect this, by using *_cmpxchg()
wherever the returned value was only tested to check if the exchange
had really taken place.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

src/cairo-atomic-private.h

@@ -61,7 +61,8 @@ typedef int cairo_atomic_int_t;
 
 # define _cairo_atomic_int_inc(x) ((void) __sync_fetch_and_add(x, 1))
 # define _cairo_atomic_int_dec_and_test(x) (__sync_fetch_and_add(x, -1) == 1)
-# define _cairo_atomic_int_cmpxchg(x, oldv, newv) __sync_val_compare_and_swap (x, oldv, newv)
+# define _cairo_atomic_int_cmpxchg(x, oldv, newv) __sync_bool_compare_and_swap (x, oldv, newv)
+# define _cairo_atomic_int_cmpxchg_return_old(x, oldv, newv) __sync_val_compare_and_swap (x, oldv, newv)
 
 #if SIZEOF_VOID_P==SIZEOF_INT
 typedef int cairo_atomic_intptr_t;
@@ -74,7 +75,10 @@ typedef long long cairo_atomic_intptr_t;
 #endif
 
 # define _cairo_atomic_ptr_cmpxchg(x, oldv, newv) \
-    (void*)__sync_val_compare_and_swap ((cairo_atomic_intptr_t*)x, (cairo_atomic_intptr_t)oldv, (cairo_atomic_intptr_t)newv)
+    __sync_bool_compare_and_swap ((cairo_atomic_intptr_t*)x, (cairo_atomic_intptr_t)oldv, (cairo_atomic_intptr_t)newv)
+
+# define _cairo_atomic_ptr_cmpxchg_return_old(x, oldv, newv) \
+    _cairo_atomic_intptr_to_voidptr (__sync_val_compare_and_swap ((cairo_atomic_intptr_t*)x, (cairo_atomic_intptr_t)oldv, (cairo_atomic_intptr_t)newv))
 
 #endif
 
@@ -89,7 +93,7 @@ typedef  AO_t cairo_atomic_int_t;
 
 # define _cairo_atomic_int_inc(x) ((void) AO_fetch_and_add1_full(x))
 # define _cairo_atomic_int_dec_and_test(x) (AO_fetch_and_sub1_full(x) == 1)
-# define _cairo_atomic_int_cmpxchg(x, oldv, newv) ((cairo_atomic_int_t) AO_compare_and_swap_full(x, oldv, newv) ? oldv : *x)
+# define _cairo_atomic_int_cmpxchg(x, oldv, newv) AO_compare_and_swap_full(x, oldv, newv)
 
 #if SIZEOF_VOID_P==SIZEOF_INT
 typedef unsigned int cairo_atomic_intptr_t;
@@ -101,8 +105,9 @@ typedef unsigned long long cairo_atomic_intptr_t;
 #error No matching integer pointer type
 #endif
 
+# define _cairo_atomic_ptr_get(x) _cairo_atomic_intptr_to_voidptr (AO_load_full (x))
 # define _cairo_atomic_ptr_cmpxchg(x, oldv, newv) \
-    (void*) (cairo_atomic_intptr_t) _cairo_atomic_int_cmpxchg ((cairo_atomic_intptr_t*)(x), (cairo_atomic_intptr_t)oldv, (cairo_atomic_intptr_t)newv)
+    _cairo_atomic_int_cmpxchg ((cairo_atomic_intptr_t*)(x), (cairo_atomic_intptr_t)oldv, (cairo_atomic_intptr_t)newv)
 
 #endif
 
@@ -118,10 +123,13 @@ cairo_private cairo_bool_t
 _cairo_atomic_int_dec_and_test (int *x);
 
 cairo_private int
-_cairo_atomic_int_cmpxchg (int *x, int oldv, int newv);
+_cairo_atomic_int_cmpxchg_return_old_impl (int *x, int oldv, int newv);
 
 cairo_private void *
-_cairo_atomic_ptr_cmpxchg (void **x, void *oldv, void *newv);
+_cairo_atomic_ptr_cmpxchg_return_old_impl (void **x, void *oldv, void *newv);
+
+#define _cairo_atomic_int_cmpxchg_return_old(x, oldv, newv) _cairo_atomic_int_cmpxchg_return_old_impl (x, oldv, newv)
+#define _cairo_atomic_ptr_cmpxchg_return_old(x, oldv, newv) _cairo_atomic_ptr_cmpxchg_return_old_impl (x, oldv, newv)
 
 #ifdef ATOMIC_OP_NEEDS_MEMORY_BARRIER
 cairo_private int
@@ -130,6 +138,54 @@ _cairo_atomic_int_get (int *x);
 # define _cairo_atomic_int_get(x) (*x)
 #endif
 
+#else
+
+/* Workaround GCC complaining about casts */
+static cairo_always_inline void *
+_cairo_atomic_intptr_to_voidptr (cairo_atomic_intptr_t x)
+{
+  return (void *) x;
+}
+
+static cairo_always_inline cairo_atomic_int_t
+_cairo_atomic_int_cmpxchg_return_old_fallback(cairo_atomic_int_t *x, cairo_atomic_int_t oldv, cairo_atomic_int_t newv)
+{
+    cairo_atomic_int_t curr;
+
+    do {
+        curr = _cairo_atomic_int_get (x);
+    } while (curr == oldv && !_cairo_atomic_int_cmpxchg (x, oldv, newv));
+
+    return curr;
+}
+
+static cairo_always_inline void *
+_cairo_atomic_ptr_cmpxchg_return_old_fallback(void **x, void *oldv, void *newv)
+{
+    void *curr;
+
+    do {
+        curr = _cairo_atomic_ptr_get (x);
+    } while (curr == oldv && !_cairo_atomic_ptr_cmpxchg (x, oldv, newv));
+
+    return curr;
+}
+#endif
+
+#ifndef _cairo_atomic_int_cmpxchg_return_old
+#define _cairo_atomic_int_cmpxchg_return_old(x, oldv, newv) _cairo_atomic_int_cmpxchg_return_old_fallback (x, oldv, newv)
+#endif
+
+#ifndef _cairo_atomic_ptr_cmpxchg_return_old
+#define _cairo_atomic_ptr_cmpxchg_return_old(x, oldv, newv) _cairo_atomic_ptr_cmpxchg_return_old_fallback (x, oldv, newv)
+#endif
+
+#ifndef _cairo_atomic_int_cmpxchg
+#define _cairo_atomic_int_cmpxchg(x, oldv, newv) (_cairo_atomic_int_cmpxchg_return_old (x, oldv, newv) == oldv)
+#endif
+
+#ifndef _cairo_atomic_ptr_cmpxchg
+#define _cairo_atomic_ptr_cmpxchg(x, oldv, newv) (_cairo_atomic_ptr_cmpxchg_return_old (x, oldv, newv) == oldv)
 #endif
 
 #define _cairo_atomic_uint_get(x) _cairo_atomic_int_get(x)

src/cairo-atomic.c

@@ -62,7 +62,7 @@ _cairo_atomic_int_dec_and_test (int *x)
 }
 
 int
-_cairo_atomic_int_cmpxchg (int *x, int oldv, int newv)
+_cairo_atomic_int_cmpxchg_return_old_impl (int *x, int oldv, int newv)
 {
     int ret;
 
@@ -76,7 +76,7 @@ _cairo_atomic_int_cmpxchg (int *x, int oldv, int newv)
 }
 
 void *
-_cairo_atomic_ptr_cmpxchg (void **x, void *oldv, void *newv)
+_cairo_atomic_ptr_cmpxchg_return_old_impl (void **x, void *oldv, void *newv)
 {
     void *ret;
 

src/cairo-freed-pool-private.h

@@ -53,13 +53,13 @@ typedef struct {
 static inline void *
 _atomic_fetch (void **slot)
 {
-    return _cairo_atomic_ptr_cmpxchg (slot, *slot, NULL);
+    return _cairo_atomic_ptr_cmpxchg_return_old (slot, *slot, NULL);
 }
 
 static inline cairo_bool_t
 _atomic_store (void **slot, void *ptr)
 {
-    return _cairo_atomic_ptr_cmpxchg (slot, NULL, ptr) == NULL;
+    return _cairo_atomic_ptr_cmpxchg (slot, NULL, ptr);
 }
 
 cairo_private void *

src/cairo-image-surface.c

@@ -873,7 +873,7 @@ _pixman_transparent_image (void)
 	image = pixman_image_create_solid_fill (&color);
 
 	if (_cairo_atomic_ptr_cmpxchg (&__pixman_transparent_image,
-				       NULL, image) == NULL)
+				       NULL, image))
 	{
 	    pixman_image_ref (image);
 	}
@@ -902,7 +902,7 @@ _pixman_black_image (void)
 	image = pixman_image_create_solid_fill (&color);
 
 	if (_cairo_atomic_ptr_cmpxchg (&__pixman_black_image,
-				       NULL, image) == NULL)
+				       NULL, image))
 	{
 	    pixman_image_ref (image);
 	}
@@ -931,7 +931,7 @@ _pixman_white_image (void)
 	image = pixman_image_create_solid_fill (&color);
 
 	if (_cairo_atomic_ptr_cmpxchg (&__pixman_white_image,
-				       NULL, image) == NULL)
+				       NULL, image))
 	{
 	    pixman_image_ref (image);
 	}

src/cairo.c

@@ -142,7 +142,7 @@ _context_get (void)
 	    return malloc (sizeof (cairo_t));
 
 	new = old | (1 << avail);
-    } while (_cairo_atomic_int_cmpxchg (&_context_stash.occupied, old, new) != old);
+    } while (! _cairo_atomic_int_cmpxchg (&_context_stash.occupied, old, new));
 
     return &_context_stash.pool[avail];
 }
@@ -163,7 +163,7 @@ _context_put (cairo_t *cr)
     do {
 	old = _cairo_atomic_int_get (&_context_stash.occupied);
 	new = old & avail;
-    } while (_cairo_atomic_int_cmpxchg (&_context_stash.occupied, old, new) != old);
+    } while (! _cairo_atomic_int_cmpxchg (&_context_stash.occupied, old, new));
 }
 #else
 #define _context_get() malloc (sizeof (cairo_t))

src/drm/cairo-drm.c

@@ -84,7 +84,7 @@ _device_finish (void *abstract_device)
     CAIRO_MUTEX_UNLOCK (_cairo_drm_device_mutex);
 
     if (_cairo_atomic_ptr_cmpxchg (&_cairo_drm_default_device,
-				   device, NULL) == device)
+				   device, NULL))
     {
 	cairo_device_destroy (&device->base);
     }