proplib: use GCC atomic builtins if supported.

NEWS

@@ -1,3 +1,9 @@
+xbps-0.42 (???):
+
+ * Use atomic builtins if supported by the compiler in our
+   portableproplib copy, to handle object reference counting.
+   This should be cheaper than using a mutex.
+
 xbps-0.41 (2014-09-29):
 
  * libxbps: another bugfix while checking required shlibs in

configure

@@ -340,6 +340,31 @@ echo "CPPFLAGS +=       -I\$(TOPDIR)/lib/portableproplib/prop" >>$CONFIG_MK
 echo "LDFLAGS +=	-lpthread" >>$CONFIG_MK
 echo "STATIC_LIBS +=	-lpthread" >>$CONFIG_MK
 
+#
+# Check for GCC atomic builtins.
+#
+func=atomic
+printf "Checking for GCC atomic builtins ... "
+cat <<EOF >_$func.c
+int main() {
+	volatile unsigned long val = 1;
+	__sync_fetch_and_add(&val, 1);
+	__sync_fetch_and_sub(&val, 1);
+	__sync_add_and_fetch(&val, 1);
+	__sync_sub_and_fetch(&val, 1);
+	return 0;
+}
+EOF
+if $XCC _$func.c -o _$func 2>/dev/null; then
+	echo yes.
+	HAVE_ATOMICS=1
+else
+	echo no.
+fi
+rm -f _$func.c _$func
+if test -n "$HAVE_ATOMICS"; then
+	echo "CPPFLAGS +=	-DHAVE_ATOMICS" >> $CONFIG_MK
+fi
 #
 # Check for vasprintf().
 #

lib/portableproplib/prop_object_impl.h

@@ -277,36 +277,58 @@ struct _prop_object_iterator {
 	static pthread_once_t x = PTHREAD_ONCE_INIT;
 #define _PROP_ONCE_RUN(x,f)		pthread_once(&(x),(void(*)(void))f)
 
+#ifndef HAVE_ATOMICS /* NO ATOMIC SUPPORT, USE A MUTEX */
+
 #define _PROP_NEED_REFCNT_MTX
+#define _PROP_ATOMIC_INC32(x) \
+	do { \
+		pthread_mutex_lock(&_prop_refcnt_mtx); \
+		(*(x))++; \
+		pthread_mutex_unlock(&_prop_refcnt_mtx); \
+	} while (/*CONSTCOND*/0)
+#define _PROP_ATOMIC_DEC32(x) \
+	do { \
+		pthread_mutex_lock(&_prop_refcnt_mtx); \
+		(*(x))--; \
+		pthread_mutex_unlock(&_prop_refcnt_mtx); \
+	} while (/*CONSTCOND*/0)
+#define _PROP_ATOMIC_INC32_NV(x, v) \
+	do { \
+		pthread_mutex_lock(&_prop_refcnt_mtx); \
+		v = ++(*(x)); \
+		pthread_mutex_unlock(&_prop_refcnt_mtx); \
+	} while (/*CONSTCOND*/0)
+#define _PROP_ATOMIC_DEC32_NV(x, v) \
+	do { \
+		pthread_mutex_lock(&_prop_refcnt_mtx); \
+		v = --(*(x)); \
+		pthread_mutex_unlock(&_prop_refcnt_mtx); \
+	} while (/*CONSTCOND*/0)
+
+#else /* GCC ATOMIC BUILTINS */
 
 #define _PROP_ATOMIC_INC32(x)						\
 do {									\
-	pthread_mutex_lock(&_prop_refcnt_mtx);				\
+	(void)__sync_fetch_and_add(x, 1);				\
-	(*(x))++;							\
-	pthread_mutex_unlock(&_prop_refcnt_mtx);			\
 } while (/*CONSTCOND*/0)
 
 #define _PROP_ATOMIC_DEC32(x)						\
 do {									\
-	pthread_mutex_lock(&_prop_refcnt_mtx);				\
+	(void)__sync_fetch_and_sub(x, 1);				\
-	(*(x))--;							\
-	pthread_mutex_unlock(&_prop_refcnt_mtx);			\
 } while (/*CONSTCOND*/0)
 
 #define _PROP_ATOMIC_INC32_NV(x, v)					\
 do {									\
-	pthread_mutex_lock(&_prop_refcnt_mtx);				\
+	v = __sync_add_and_fetch(x, 1);					\
-	v = ++(*(x));							\
-	pthread_mutex_unlock(&_prop_refcnt_mtx);			\
 } while (/*CONSTCOND*/0)
 
 #define _PROP_ATOMIC_DEC32_NV(x, v)					\
 do {									\
-	pthread_mutex_lock(&_prop_refcnt_mtx);				\
+	v = __sync_sub_and_fetch(x, 1);					\
-	v = --(*(x));							\
-	pthread_mutex_unlock(&_prop_refcnt_mtx);			\
 } while (/*CONSTCOND*/0)
 
+#endif /* !HAVE_ATOMICS */
+
 /*
  * Language features.
  */