避免wait_if的counter因为ABA问题导致计数错误

Author: mutouyun

src/libipc/waiter_helper.h

@@ -33,9 +33,10 @@ struct waiter_helper {
         auto & counter = ctrl.counter();
         counter.waiting_.fetch_add(1, std::memory_order_release);
         flags.is_waiting_.store(true, std::memory_order_relaxed);
-        auto finally = ipc::guard([&counter, &flags] {
-            for (auto curr_wait = counter.waiting_.load(std::memory_order_acquire); curr_wait > 0;) {
-                if (counter.waiting_.compare_exchange_weak(curr_wait, curr_wait - 1, std::memory_order_release)) {
+        auto finally = ipc::guard([&ctrl, &counter, &flags] {
+            ctrl.get_lock(); // barrier
+            for (auto curr_wait = counter.waiting_.load(std::memory_order_relaxed); curr_wait > 0;) {
+                if (counter.waiting_.compare_exchange_weak(curr_wait, curr_wait - 1, std::memory_order_acq_rel)) {
                     break;
                 }
             }