--- /dev/null
+class eventcount
+{
+public:
+ eventcount() : waiters(0)
+ {
+ count($) = 0;
+ }
+
+ void signal_relaxed()
+ {
+ unsigned cmp = count.load(std::memory_order_relaxed);
+ signal_impl(cmp);
+ }
+
+ void signal()
+ {
+ unsigned cmp = count.fetch_add(0, std::memory_order_seq_cst);
+ signal_impl(cmp);
+ }
+
+ unsigned get()
+ {
+ unsigned cmp = count.fetch_or(0x80000000,
+std::memory_order_seq_cst);
+ return cmp & 0x7FFFFFFF;
+ }
+
+ void wait(unsigned cmp)
+ {
+ unsigned ec = count.load(std::memory_order_seq_cst);
+ if (cmp == (ec & 0x7FFFFFFF))
+ {
+ guard.lock($);
+ ec = count.load(std::memory_order_seq_cst);
+ if (cmp == (ec & 0x7FFFFFFF))
+ {
+ waiters($) += 1;
+ cv.wait(guard, $);
+ }
+ guard.unlock($);
+ }
+ }
+
+private:
+ std::atomic<unsigned> count;
+ rl::var<unsigned> waiters;
+ std::mutex guard;
+ std::condition_variable cv;
+
+ void signal_impl(unsigned cmp)
+ {
+ if (cmp & 0x80000000)
+ {
+ guard.lock($);
+ while (false == count.compare_exchange_weak(cmp,
+ (cmp + 1) & 0x7FFFFFFF, std::memory_order_relaxed));
+ unsigned w = waiters($);
+ waiters($) = 0;
+ guard.unlock($);
+ if (w)
+ cv.notify_all($);
+ }
+ }
+};