Add support for clock ticks

luprex/core/cpp/drivenengine.hpp

@@ -123,6 +123,13 @@ public:
     //
     bool closed() const { return closed_; }
 
+    // Get the channel's error message.
+    //
+    // If this is an empty string, there is no error.  If this is set,
+    // then the channel is also closed.
+    //
+    std::string error() const { return error_; }
+
     // True if the channel is in readline mode.
     //
     // Stdio always starts with this enabled, other channels always start
@@ -161,6 +168,7 @@ private:
     std::unique_ptr<StreamBuffer> sb_out_;
     int port_;
     bool closed_;
+    std::string error_;
     std::string target_;
     char readline_buf_[READLINE_MAX];
     int readline_len_;
@@ -313,7 +321,7 @@ public:
     // delete it.  Closing a channel prevents it from showing up in
     // 'drv_list_channels'.  
     //
-    void drv_notify_close(int chid);
+    void drv_notify_close(int chid, const std::string &err);
 
     // Notify the DrivenEngine that somebody connected to an incoming port.
     // This will cause the DrivenEngine to allocate a new channel and put the