Add zmq_timers support (#657)

* Add zmq_timers support

* Add zmq_timers unit tests

zmq.hpp

@@ -2794,6 +2794,85 @@ inline std::ostream &operator<<(std::ostream &os, const message_t &msg)
     return os << msg.str();
 }
 
+#if defined(ZMQ_CPP11) && defined(ZMQ_HAVE_TIMERS)
+
+class timers
+{
+  public:
+    using id_t = int;
+    using fn_t = zmq_timer_fn;
+
+#if CPPZMQ_HAS_OPTIONAL
+    using timeout_result_t = std::optional<std::chrono::milliseconds>;
+#else
+    using timeout_result_t = detail::trivial_optional<std::chrono::milliseconds>;
+#endif
+
+    timers() : _timers(zmq_timers_new())
+    {
+        if (_timers == nullptr)
+            throw error_t();
+    }
+
+    timers(const timers &other) = delete;
+    timers &operator=(const timers &other) = delete;
+
+    ~timers()
+    {
+        int rc = zmq_timers_destroy(&_timers);
+        ZMQ_ASSERT(rc == 0);
+    }
+
+    id_t add(std::chrono::milliseconds interval, zmq_timer_fn handler, void *arg)
+    {
+        id_t timer_id = zmq_timers_add(_timers, interval.count(), handler, arg);
+        if (timer_id == -1)
+            throw zmq::error_t();
+        return timer_id;
+    }
+
+    void cancel(id_t timer_id)
+    {
+        int rc = zmq_timers_cancel(_timers, timer_id);
+        if (rc == -1)
+            throw zmq::error_t();
+    }
+
+    void set_interval(id_t timer_id, std::chrono::milliseconds interval)
+    {
+        int rc = zmq_timers_set_interval(_timers, timer_id, interval.count());
+        if (rc == -1)
+            throw zmq::error_t();
+    }
+
+    void reset(id_t timer_id)
+    {
+        int rc = zmq_timers_reset(_timers, timer_id);
+        if (rc == -1)
+            throw zmq::error_t();
+    }
+
+    timeout_result_t timeout() const
+    {
+        int timeout = zmq_timers_timeout(_timers);
+        if (timeout == -1)
+            return timeout_result_t{};
+        return std::chrono::milliseconds{timeout};
+    }
+
+    void execute()
+    {
+        int rc = zmq_timers_execute(_timers);
+        if (rc == -1)
+            throw zmq::error_t();
+    }
+
+  private:
+    void *_timers;
+};
+
+#endif // defined(ZMQ_CPP11) && defined(ZMQ_HAVE_TIMERS)
+
 } // namespace zmq
 
 #endif // __ZMQ_HPP_INCLUDED__