MINOR: hathreads: add support for gcc < 4.7
Till now the use of __atomic_* gcc builtins required gcc >= 4.7. Since
some supported and quite common operating systems like CentOS 6 still
come with older versions (4.4) and the mapping to the older builtins
is reasonably simple, let's implement it.
This code is only used for gcc < 4.7. It has been quickly tested on a
machine using gcc 4.4.4 and provided expected results.
This patch should be backported to 1.8.
diff --git a/include/common/hathreads.h b/include/common/hathreads.h
index 9782ca9..503abbe 100644
--- a/include/common/hathreads.h
+++ b/include/common/hathreads.h
@@ -99,6 +99,58 @@
/* TODO: thread: For now, we rely on GCC builtins but it could be a good idea to
* have a header file regrouping all functions dealing with threads. */
+
+#if defined(__GNUC__) && (__GNUC__ < 4 || __GNUC__ == 4 && __GNUC_MINOR__ < 7)
+/* gcc < 4.7 */
+
+#define HA_ATOMIC_ADD(val, i) __sync_add_and_fetch(val, i)
+#define HA_ATOMIC_SUB(val, i) __sync_sub_and_fetch(val, i)
+#define HA_ATOMIC_AND(val, flags) __sync_and_and_fetch(val, flags)
+#define HA_ATOMIC_OR(val, flags) __sync_or_and_fetch(val, flags)
+
+/* the CAS is a bit complicated. The older API doesn't support returning the
+ * value and the swap's result at the same time. So here we take what looks
+ * like the safest route, consisting in using the boolean version guaranteeing
+ * that the operation was performed or not, and we snoop a previous value. If
+ * the compare succeeds, we return. If it fails, we return the previous value,
+ * but only if it differs from the expected one. If it's the same it's a race
+ * thus we try again to avoid confusing a possibly sensitive caller.
+ */
+#define HA_ATOMIC_CAS(val, old, new) \
+ ({ \
+ typeof((val)) __val = (val); \
+ typeof((old)) __oldp = (old); \
+ typeof(*(old)) __oldv; \
+ typeof((new)) __new = (new); \
+ int __ret; \
+ do { \
+ __oldv = *__val; \
+ __ret = __sync_bool_compare_and_swap(__val, *__oldp, __new); \
+ } while (!__ret && *__oldp == __oldv); \
+ if (!__ret) \
+ *__oldp = __oldv; \
+ __ret; \
+ })
+
+#define HA_ATOMIC_XCHG(val, new) \
+ ({ \
+ typeof((val)) __val = (val); \
+ typeof(*(val)) __old; \
+ typeof((new)) __new = (new); \
+ do { __old = *__val; \
+ } while (!__sync_bool_compare_and_swap(__val, __old, __new)); \
+ __old; \
+ })
+#define HA_ATOMIC_STORE(val, new) \
+ ({ \
+ typeof((val)) __val = (val); \
+ typeof(*(val)) __old; \
+ typeof((new)) __new = (new); \
+ do { __old = *__val; \
+ } while (!__sync_bool_compare_and_swap(__val, __old, __new)); \
+ })
+#else
+/* gcc >= 4.7 */
#define HA_ATOMIC_CAS(val, old, new) __atomic_compare_exchange_n(val, old, new, 0, 0, 0)
#define HA_ATOMIC_ADD(val, i) __atomic_add_fetch(val, i, 0)
#define HA_ATOMIC_SUB(val, i) __atomic_sub_fetch(val, i, 0)
@@ -106,6 +158,8 @@
#define HA_ATOMIC_OR(val, flags) __atomic_or_fetch(val, flags, 0)
#define HA_ATOMIC_XCHG(val, new) __atomic_exchange_n(val, new, 0)
#define HA_ATOMIC_STORE(val, new) __atomic_store_n(val, new, 0)
+#endif
+
#define HA_ATOMIC_UPDATE_MAX(val, new) \
({ \
typeof(*(val)) __old = *(val); \