minor

LuisaGroup · Dec 18, 2024 · a0cdc19 · a0cdc19
1 parent 3c7c1d1
commit a0cdc19
Showing 1 changed file with 10 additions and 0 deletions.
diff --git a/src/backends/fallback/fallback_event.cpp b/src/backends/fallback/fallback_event.cpp
@@ -6,9 +6,19 @@
 namespace luisa::compute::fallback {
 
 void FallbackEvent::signal(uint64_t fence_value) noexcept {
+#if defined(__has_builtin) && __has_builtin(__c11_atomic_fetch_max)
     using A = _Atomic(uint64_t);
     auto p = reinterpret_cast<A *>(&_fence_value);
     __c11_atomic_fetch_max(p, fence_value, __ATOMIC_RELEASE);
+#else
+    // use a CAS loop to ensure the fence value is monotonically increasing
+    auto current = _fence_value.load(std::memory_order_acquire);
+    while (current < fence_value) {
+        if (_fence_value.compare_exchange_weak(current, fence_value, std::memory_order_release, std::memory_order_acquire)) {
+            break;
+        }
+    }
+#endif
 }
 
 void FallbackEvent::wait(uint64_t fence_value) const noexcept {