Cleanup hb_refrence_count_t

src/hb-object-private.hh

diff --git a/src/hb-object-private.hh b/src/hb-object-private.hh
index 930f616..74bc3ad 100644
--- a/src/hb-object-private.hh
+++ b/src/hb-object-private.hh
@@ -38,18 +38,31 @@
 typedef struct {
   hb_atomic_int_t ref_count;
 
+#define HB_REFERENCE_COUNT_INVALID_VALUE ((hb_atomic_int_t) -1)
+#define HB_REFERENCE_COUNT_INVALID {HB_REFERENCE_COUNT_INVALID_VALUE}
+
   inline void init (int v) { ref_count = v; /* non-atomic is fine */ }
   inline int inc (void) { return hb_atomic_int_fetch_and_add (ref_count,  1); }
   inline int dec (void) { return hb_atomic_int_fetch_and_add (ref_count, -1); }
   inline void set (int v) { return hb_atomic_int_set (ref_count, v); }
+
+  /* XXX
+   *
+   * One thing I'm not sure.  The following two methods should be declared
+   * const.  However, that assumes that hb_atomic_int_get() is const.  I have
+   * a vague memory hearing from Chris Wilson or Jeff Muizelaar that atomic get
+   * is implemented as a fetch_and_add(0).  In which case it does write to the
+   * memory, and hence cannot be called on .rodata section.  But that's how we
+   * use it.
+   *
+   * If that is indeed the case, then perhaps is_invalid() should do a
+   * non-protected read of the location.
+   */
   inline int get (void) { return hb_atomic_int_get (ref_count); }
+  inline bool is_invalid (void) { return get () == HB_REFERENCE_COUNT_INVALID_VALUE; }
 
 } hb_reference_count_t;
 
-#define HB_REFERENCE_COUNT_INVALID_VALUE ((hb_atomic_int_t) -1)
-#define HB_REFERENCE_COUNT_INVALID {HB_REFERENCE_COUNT_INVALID_VALUE}
-
-#define HB_REFERENCE_COUNT_IS_INVALID(RC) ((RC).get () == HB_REFERENCE_COUNT_INVALID_VALUE)
 
 
 /* Debug */
@@ -77,7 +90,7 @@
 /* Object allocation and lifecycle manamgement macros */
 
 #define HB_OBJECT_IS_INERT(obj) \
-    (unlikely (HB_REFERENCE_COUNT_IS_INVALID ((obj)->ref_count)))
+    (unlikely ((obj)->ref_count.is_invalid ()))
 
 #define HB_OBJECT_DO_INIT_EXPR(obj) \
     obj->ref_count.init (1)

src/hb-private.hh

diff --git a/src/hb-private.hh b/src/hb-private.hh
index d08a4d0..ae52889 100644
--- a/src/hb-private.hh
+++ b/src/hb-private.hh
@@ -212,7 +212,7 @@
 
 #include <glib.h>
 
-typedef int hb_atomic_int_t;
+typedef volatile int hb_atomic_int_t;
 #define hb_atomic_int_fetch_and_add(AI, V)	g_atomic_int_exchange_and_add (&(AI), V)
 #define hb_atomic_int_get(AI)			g_atomic_int_get (&(AI))
 #define hb_atomic_int_set(AI, V)		g_atomic_int_set (&(AI), V)
@@ -235,12 +235,12 @@
 #warning "Could not find any system to define platform macros, library will NOT be thread-safe"
 #endif
 
-typedef int hb_atomic_int_t;
+typedef volatile int hb_atomic_int_t;
 #define hb_atomic_int_fetch_and_add(AI, V)	((AI) += (V), (AI) - (V))
 #define hb_atomic_int_get(AI)			(AI)
 #define hb_atomic_int_set(AI, V)		HB_STMT_START { (AI) = (V); } HB_STMT_END
 
-typedef int hb_mutex_t;
+typedef volatile int hb_mutex_t;
 #define HB_MUTEX_INIT				0
 #define hb_mutex_init(M)			HB_STMT_START { (M) = 0; } HB_STMT_END
 #define hb_mutex_lock(M)			HB_STMT_START { (M) = 1; } HB_STMT_END