Surround initialisations with atomic critical section

Fixes the race condition when one thread uses cairo_mask_compositor_t
pointer returned by _cairo_image_mask_compositor_get, while another one
started but has not finished it's initialisation yet

Usage:
static cairo_atomic_once_t once = CAIRO_ATOMIC_ONCE_INIT;
if (_cairo_atomic_init_once_enter(&once)) {
    /* Initialization code */
    _cairo_atomic_init_once_leave(&once);
}

https://bugs.freedesktop.org/show_bug.cgi?id=103037

1 files changed, 33 insertions, 0 deletions

diff --git a/src/cairo-atomic-private.h b/src/cairo-atomic-private.h
index 500129039..723a326ce 100644
--- a/src/cairo-atomic-private.h
+++ b/src/cairo-atomic-private.h
@@ -45,6 +45,8 @@
 #include "config.h"
 #endif
 
+#include <assert.h>
+
 /* The autoconf on OpenBSD 4.5 produces the malformed constant name
  * SIZEOF_VOID__ rather than SIZEOF_VOID_P.  Work around that here. */
 #if !defined(SIZEOF_VOID_P) && defined(SIZEOF_VOID__)
@@ -393,6 +395,37 @@ _cairo_atomic_ptr_cmpxchg_return_old_fallback(void **x, void *oldv, void *newv)
     (void) ret__; \
 } while (0)
 
+typedef cairo_atomic_int_t cairo_atomic_once_t;
+
+#define CAIRO_ATOMIC_ONCE_UNINITIALIZED (0)
+#define CAIRO_ATOMIC_ONCE_INITIALIZING  (1)
+#define CAIRO_ATOMIC_ONCE_INITIALIZED   (2)
+#define CAIRO_ATOMIC_ONCE_INIT          CAIRO_ATOMIC_ONCE_UNINITIALIZED
+
+static cairo_always_inline cairo_bool_t
+_cairo_atomic_init_once_enter(cairo_atomic_once_t *once)
+{
+    if (likely(_cairo_atomic_int_get(once) == CAIRO_ATOMIC_ONCE_INITIALIZED))
+	return 0;
+
+    if (_cairo_atomic_int_cmpxchg(once,
+				  CAIRO_ATOMIC_ONCE_UNINITIALIZED,
+				  CAIRO_ATOMIC_ONCE_INITIALIZING))
+	return 1;
+
+    while (_cairo_atomic_int_get(once) != CAIRO_ATOMIC_ONCE_INITIALIZED) {}
+    return 0;
+}
+
+static cairo_always_inline void
+_cairo_atomic_init_once_leave(cairo_atomic_once_t *once)
+{
+    if (unlikely(!_cairo_atomic_int_cmpxchg(once,
+					    CAIRO_ATOMIC_ONCE_INITIALIZING,
+					    CAIRO_ATOMIC_ONCE_INITIALIZED)))
+	assert (0 && "incorrect use of _cairo_atomic_init_once API (once != CAIRO_ATOMIC_ONCE_INITIALIZING)");
+}
+
 CAIRO_END_DECLS
 
 #endif