Designed and implemented by Chris M. Thomasson. Complete implementation can be found on GitHub.
mutex.h:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 |
class rw_fast_mutex { public: rw_fast_mutex() : m_wrstate(1), m_count(INT_MAX), m_rdwake(0), m_rdwset(0), m_wrwset(0), m_wrmtx(0) {} void read_lock() { if (m_count.fetch_add(-1, std::memory_order_acquire) < 1) m_rdwset.wait(); } void read_unlock() { if (m_count.fetch_add(1, std::memory_order_release) < 0) if (m_rdwake.fetch_add(-1, std::memory_order_acq_rel) == 1) m_wrwset.post(); } void write_lock() { if (m_wrstate.fetch_sub(1, std::memory_order_acquire) < 1) m_wrmtx.wait(); int count = m_count.fetch_add(-INT_MAX, std::memory_order_acquire); if (count < INT_MAX) { int rdwake = m_rdwake.fetch_add(INT_MAX - count, std::memory_order_acquire); if (rdwake + INT_MAX - count) m_wrwset.wait(); } } void write_unlock() { int count = m_count.fetch_add(INT_MAX, std::memory_order_release); if (count < 0) m_rdwset.post(-count); if (m_wrstate.fetch_add(1, std::memory_order_release) < 0) m_wrmtx.post(); } private: std::atomic<int> m_wrstate; std::atomic<int> m_count; std::atomic<int> m_rdwake; semaphore m_rdwset; semaphore m_wrwset; semaphore m_wrmtx; }; |
Thanks for your interest in my algorithm. I had a fun time creating it back in 2007-2008. It was interesting to think up a scheme that can get around any CAS loops. Also, this is 100% starvation free. Nice. :^)