I recently found that in Qt, reference counting to guard a resource, is using ref() / deref()
But ref() is using memory_order_seq_cst while memory_order_relaxed, should be sufficient What is important is to guarantee that destruction is not subject to a race condition, to prevent double destruction. Hence deref() with memory_order_seq_cst is enough to guarantee that. It does not matter how much the counter increase, but what is important is to control how it is decreased. Hence deref(with memory_order_seq_cst) is just enough. I have verified the implementaiton of reference counting for shared_ptr in clang, and it does what I describe above (it even just use memory_order_acq_rel to decrement, and not memory_order_seq_cst) https://github.com/llvm-mirror/libcxx/blob/master/include/memory#L3344 Is there a reason why Qt is not optimized in the same way? (since ref() is used a lot, and atomic operations are a bit expensive). Is there a requirement at some stage that the reference counter must be ordered for increments? Philippe _______________________________________________ Development mailing list Development@qt-project.org https://lists.qt-project.org/listinfo/development
