| "Chris M. Thomasson" <invalid_chris_thomasson@invalid.invalid>: Mar 31 01:44PM -0700 Notice how there is an acquire barrier inside of the CAS loops within the enqueue and dequeue functions of: http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue ? Well, fwiw we can get rid of them by using stand alone fences: Btw, sorry for the membar abstraction. I can quickly get sick and tired of having to type out (std::memory_order_relaxed) all the damn time. ;^) Anyway, here is the simple code using Relacy: ___________________ /* Membar Abstraction ___________________________________________________*/ #define mbrlx std::memory_order_relaxed #define mbacq std::memory_order_acquire #define mbrel std::memory_order_release #define mb(mb_membar) std::atomic_thread_fence(mb_membar) template<typename T, unsigned int T_N> struct fifo { struct cell { VAR_T(T) m_data; std::atomic<unsigned int> m_ver; }; std::atomic<unsigned int> m_head; std::atomic<unsigned int> m_tail; cell m_cells[T_N]; fifo() : m_head(0), m_tail(0) { for (unsigned int i = 0; i < T_N; ++i) { m_cells[i].m_ver.store(i, mbrlx); } } bool push_try(T const& data) { cell* c = nullptr; unsigned int ver = m_head.load(mbrlx); do { c = &m_cells[ver & (T_N - 1)]; if (c->m_ver.load(mbrlx) != ver) return false; } while (! m_head.compare_exchange_weak(ver, ver + 1, mbrlx)); mb(mbacq); VAR(c->m_data) = data; mb(mbrel); c->m_ver.store(ver + 1, mbrlx); return true; } bool pop_try(T& data) { cell* c = nullptr; unsigned int ver = m_tail.load(mbrlx); do { c = &m_cells[ver & (T_N - 1)]; if (c->m_ver.load(mbrlx) != ver + 1) return false; } while (! m_tail.compare_exchange_weak(ver, ver + 1, mbrlx)); mb(mbacq); data = VAR(c->m_data); mb(mbrel); c->m_ver.store(ver + T_N, mbrlx); return true; } }; ___________________ There is no need for any membars within the loops. The version count keeps everything in order. :^) |
| Andrey Karpov <karpov2007@gmail.com>: Mar 31 11:50AM -0700 A new version of the PVS-Studio analyzer 6.23 is working under macOS, which allows you to check the projects written in C and C++. Our team decided to perform a XNU Kernel check to coincide it with this event. https://www.viva64.com/en/b/0566/ |
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