spsc-bugfix/eventcount-relacy.h

   1 class eventcount
   2 {
   3 public:
   4         eventcount() : waiters(0)
   5         {
   6                 count($) = 0;
   7         }
   8
   9         void signal_relaxed()
  10         {
  11                 unsigned cmp = count.load(std::memory_order_relaxed);
  12                 signal_impl(cmp);
  13         }
  14
  15         void signal()
  16         {
  17                 unsigned cmp = count.fetch_add(0, std::memory_order_seq_cst);
  18                 signal_impl(cmp);
  19         }
  20
  21         unsigned get()
  22         {
  23                 unsigned cmp = count.fetch_or(0x80000000,
  24 std::memory_order_seq_cst);
  25                 return cmp & 0x7FFFFFFF;
  26         }
  27
  28         void wait(unsigned cmp)
  29         {
  30                 unsigned ec = count.load(std::memory_order_seq_cst);
  31                 if (cmp == (ec & 0x7FFFFFFF))
  32                 {
  33                         guard.lock($);
  34                         ec = count.load(std::memory_order_seq_cst);
  35                         if (cmp == (ec & 0x7FFFFFFF))
  36                         {
  37                                 waiters($) += 1;
  38                                 cv.wait(guard, $);
  39                         }
  40                         guard.unlock($);
  41                 }
  42         }
  43
  44 private:
  45         std::atomic<unsigned> count;
  46         rl::var<unsigned> waiters;
  47         std::mutex guard;
  48         std::condition_variable cv;
  49
  50         void signal_impl(unsigned cmp)
  51         {
  52                 if (cmp & 0x80000000)
  53                 {
  54                         guard.lock($);
  55                         while (false == count.compare_exchange_weak(cmp,
  56                                 (cmp + 1) & 0x7FFFFFFF, std::memory_order_relaxed));
  57                         unsigned w = waiters($);
  58                         waiters($) = 0;
  59                         guard.unlock($);
  60                         if (w)
  61                                 cv.notify_all($);
  62                 }
  63         }
  64 };