spsc-queue-scfence/eventcount.h

   1 #include <unrelacy.h>
   2 #include <atomic>
   3 #include <mutex>
   4 #include <condition_variable>
   5 #include "wildcard.h"
   6
   7 class eventcount
   8 {
   9 public:
  10         eventcount() : waiters(0)
  11         {
  12                 count = 0;
  13         }
  14
  15         void signal_relaxed()
  16         {
  17                 unsigned cmp = count.load(wildcard(1)); // relaxed
  18                 signal_impl(cmp);
  19         }
  20
  21         void signal()
  22         {
  23                 unsigned cmp = count.fetch_add(0, std::memory_order_seq_cst); // the fix
  24                 signal_impl(cmp);
  25         }
  26
  27         unsigned get()
  28         {
  29                 unsigned cmp = count.fetch_or(0x80000000, wildcard(2)); // sc
  30                 return cmp & 0x7FFFFFFF;
  31         }
  32
  33         void wait(unsigned cmp)
  34         {
  35                 unsigned ec = count.load(wildcard(3)); // sc
  36                 if (cmp == (ec & 0x7FFFFFFF))
  37                 {
  38                         guard.lock($);
  39                         ec = count.load(wildcard(4)); // sc
  40                         if (cmp == (ec & 0x7FFFFFFF))
  41                         {
  42                                 waiters += 1;
  43                                 cv.wait(guard);
  44                         }
  45                         guard.unlock($);
  46                 }
  47         }
  48
  49 private:
  50         std::atomic<unsigned> count;
  51         rl::var<unsigned> waiters;
  52         std::mutex guard;
  53         std::condition_variable cv;
  54
  55         void signal_impl(unsigned cmp)
  56         {
  57                 if (cmp & 0x80000000)
  58                 {
  59                         guard.lock($);
  60                         while (false == count.compare_exchange_weak(cmp,
  61                                 (cmp + 1) & 0x7FFFFFFF, wildcard(5))); // relaxed
  62                         unsigned w = waiters($);
  63                         waiters = 0;
  64                         guard.unlock($);
  65                         if (w)
  66                                 cv.notify_all($);
  67                 }
  68         }
  69 };