spsc-queue/eventcount.h

   1 #include <unrelacy.h>
   2
   3 class eventcount
   4 {
   5 public:
   6         eventcount()
   7                 : count(0)
   8                 , waiters(0)
   9         {}
  10
  11         void signal_relaxed()
  12         {
  13                 unsigned cmp = count.load(std::memory_order_relaxed);
  14                 signal_impl(cmp);
  15         }
  16
  17         void signal()
  18         {
  19                 unsigned cmp = count.fetch_add(0, std::memory_order_seq_cst);
  20                 signal_impl(cmp);
  21         }
  22
  23         unsigned get()
  24         {
  25                 unsigned cmp = count.fetch_or(0x80000000,
  26 std::memory_order_seq_cst);
  27                 return cmp & 0x7FFFFFFF;
  28         }
  29
  30         void wait(unsigned cmp)
  31         {
  32                 unsigned ec = count.load(std::memory_order_seq_cst);
  33                 if (cmp == (ec & 0x7FFFFFFF))
  34                 {
  35                         guard.lock($);
  36                         ec = count.load(std::memory_order_seq_cst);
  37                         if (cmp == (ec & 0x7FFFFFFF))
  38                         {
  39                                 waiters += 1;
  40                                 cv.wait(guard, $);
  41                         }
  42                         guard.unlock($);
  43                 }
  44         }
  45
  46 private:
  47         std::atomic<unsigned> count;
  48         rl::var<unsigned> waiters;
  49         mutex guard;
  50         condition_variable_any cv;
  51
  52         void signal_impl(unsigned cmp)
  53         {
  54                 if (cmp & 0x80000000)
  55                 {
  56                         guard.lock($);
  57                         while (false == count.compare_swap(cmp,
  58                                 (cmp + 1) & 0x7FFFFFFF, std::memory_order_relaxed));
  59                         unsigned w = waiters($);
  60                         waiters = 0;
  61                         guard.unlock($);
  62                         if (w)
  63                                 cv.notify_all($);
  64                 }
  65         }
  66 };