Improve ethread atomics

The ethread atomics API now also provide double word size atomics.
Double word size atomics are implemented using native atomic
instructions on x86 (when the cmpxchg8b instruction is available)
and on x86_64 (when the cmpxchg16b instruction is available). On
other hardware where 32-bit atomics or word size atomics are
available, an optimized fallback is used; otherwise, a spinlock,
or a mutex based fallback is used.

The ethread library now performs runtime tests for presence of
hardware features, such as for example SSE2 instructions, instead
of requiring this to be determined at compile time.

There are now functions implementing each atomic operation with the
following implied memory barrier semantics: none, read, write,
acquire, release, and full. Some of the operation-barrier
combinations aren't especially useful. But instead of filtering
useful ones out, and potentially miss a useful one, we implement
them all.

A much smaller set of functionality for native atomics are required
to be implemented than before. More or less only cmpxchg and a
membar macro are required to be implemented for each atomic size.
Other functions will automatically be constructed from these. It is,
of course, often wise to implement more that this if possible from a
performance perspective.

1 files changed, 3 insertions, 5 deletions

diff --git a/erts/include/internal/pthread/ethr_event.h b/erts/include/internal/pthread/ethr_event.h
index 4c29b28536..d0a77990cc 100644
--- a/erts/include/internal/pthread/ethr_event.h
+++ b/erts/include/internal/pthread/ethr_event.h
@@ -21,7 +21,7 @@
  * Author: Rickard Green
  */
 
-#if defined(ETHR_HAVE_LINUX_FUTEX) && defined(ETHR_HAVE_NATIVE_ATOMICS)
+#if defined(ETHR_HAVE_LINUX_FUTEX) && defined(ETHR_HAVE_32BIT_NATIVE_ATOMIC_OPS)
 /* --- Linux futex implementation of ethread events ------------------------- */
 #define ETHR_LINUX_FUTEX_IMPL__
 
@@ -62,8 +62,7 @@ static void ETHR_INLINE
 ETHR_INLINE_FUNC_NAME_(ethr_event_set)(ethr_event *e)
 {
     ethr_sint32_t val;
-    ETHR_MEMORY_BARRIER;
-    val = ethr_atomic32_xchg(&e->futex, ETHR_EVENT_ON__);
+    val = ethr_atomic32_xchg_mb(&e->futex, ETHR_EVENT_ON__);
     if (val == ETHR_EVENT_OFF_WAITER__) {
 	int res = ETHR_FUTEX__(&e->futex, ETHR_FUTEX_WAKE__, 1);
 	if (res != 0)
@@ -99,8 +98,7 @@ static void ETHR_INLINE
 ETHR_INLINE_FUNC_NAME_(ethr_event_set)(ethr_event *e)
 {
     ethr_sint32_t val;
-    ETHR_MEMORY_BARRIER;
-    val = ethr_atomic32_xchg(&e->state, ETHR_EVENT_ON__);
+    val = ethr_atomic32_xchg_mb(&e->state, ETHR_EVENT_ON__);
     if (val == ETHR_EVENT_OFF_WAITER__) {
 	int res = pthread_mutex_lock(&e->mtx);
 	if (res != 0)