[cairo-atomic] Use an atomic operation to set the status on a shared resource.

Since the objects can be shared and may be in use simultaneously across
multiple threads, setting the status needs to be atomic. We use a
locked compare and exchange in order to avoid overwriting an existing
error - that is we use an atomic operation that only sets the new status
value if the current value is CAIRO_STATUS_SUCCESS.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/cairo-atomic-private.h b/src/cairo-atomic-private.h
index 3577e0d32..3bf4e2754 100644
--- a/src/cairo-atomic-private.h
+++ b/src/cairo-atomic-private.h
@@ -54,6 +54,8 @@ typedef int cairo_atomic_int_t;
 # define _cairo_atomic_int_get(x) (*x)
 # define _cairo_atomic_int_set(x, value) ((*x) = value)
 
+# define _cairo_atomic_int_cmpxchg(x, oldv, newv) __sync_val_compare_and_swap (x, oldv, newv)
+
 #else
 
 # include "cairo-compiler-private.h"
@@ -74,8 +76,14 @@ _cairo_atomic_int_get (int *x);
 cairo_private void
 _cairo_atomic_int_set (int *x, int value);
 
+cairo_private int
+_cairo_atomic_int_cmpxchg (int *x, int oldv, int newv);
+
 #endif
 
+#define _cairo_status_set_error(status, err) \
+    (void) _cairo_atomic_int_cmpxchg (status, CAIRO_STATUS_SUCCESS, err)
+
 CAIRO_END_DECLS
 
 #endif