spsc-queue/eventcount.h

   1 #include <unrelacy.h>
   2 #include <atomic>
   3 #include <mutex>
   4
   5 class eventcount
   6 {
   7 public:
   8         eventcount() : waiters(0)
   9         {
  10                 count = 0;
  11         }
  12
  13         void signal_relaxed()
  14         {
  15                 unsigned cmp = count.load(std::memory_order_relaxed);
  16                 signal_impl(cmp);
  17         }
  18
  19         void signal()
  20         {
  21                 unsigned cmp = count.fetch_add(0, std::memory_order_seq_cst);
  22                 signal_impl(cmp);
  23         }
  24
  25         unsigned get()
  26         {
  27                 unsigned cmp = count.fetch_or(0x80000000,
  28 std::memory_order_seq_cst);
  29                 return cmp & 0x7FFFFFFF;
  30         }
  31
  32         void wait(unsigned cmp)
  33         {
  34                 unsigned ec = count.load(std::memory_order_seq_cst);
  35                 if (cmp == (ec & 0x7FFFFFFF))
  36                 {
  37                         guard.lock($);
  38                         ec = count.load(std::memory_order_seq_cst);
  39                         if (cmp == (ec & 0x7FFFFFFF))
  40                         {
  41                                 waiters += 1;
  42                                 cv.wait(guard, $);
  43                         }
  44                         guard.unlock($);
  45                 }
  46         }
  47
  48 private:
  49         std::atomic<unsigned> count;
  50         rl::var<unsigned> waiters;
  51         std::mutex guard;
  52         condition_variable_any cv;
  53
  54         void signal_impl(unsigned cmp)
  55         {
  56                 if (cmp & 0x80000000)
  57                 {
  58                         guard.lock($);
  59                         while (false == count.compare_exchange_weak(cmp,
  60                                 (cmp + 1) & 0x7FFFFFFF, std::memory_order_relaxed));
  61                         unsigned w = waiters($);
  62                         waiters = 0;
  63                         guard.unlock($);
  64                         if (w)
  65                                 cv.notify_all($);
  66                 }
  67         }
  68 };