add cancel sync, filter out wait for canceled tasks

src/thread/future.cpp

@@ -27,6 +27,7 @@ namespace fc {
   }
                
   void promise_base::cancel(const char* reason /* = nullptr */){
+      synchronized(_spin_yield)
 //      wlog("${desc} canceled!", ("desc", _desc? _desc : ""));
       _canceled = true;
 #ifndef NDEBUG

src/thread/thread_d.hpp

@@ -596,7 +596,12 @@ namespace fc {
                   else if( timeout_time != time_point::min() ) 
                   {
                      // there may be tasks that have been canceled we should filter them out now
-                     // rather than waiting... 
+                     // rather than waiting...
+		     //
+
+		     if (current->canceled){
+			     return;
+		     }
 
 
                     /* This bit is kind of sloppy -- this wait was originally implemented as a wait