improved 'when', fixed simul.disconnect

@@ -411,13 +411,19 @@ class ShellRunner (Runner) :
         """
         for evt in event :
             self.watch(evt)
-    async def cmd_when (self, event:str, cmd:str, *args:str) :
+    async def cmd_when (self, event:str, count:int, cmd:str, *args:str) :
         """execute command on specified event
+         - event: watched event
+         - count: number of occurrences (0 => infinite)
          - cmd: a shell command
          - args: arguments for cmd"""
         def cb (e, *a) :
             loop = asyncio.get_event_loop()
             asyncio.run_coroutine_threadsafe(self._cmd_call(cmd, args), loop)
+            cb.count -= 1
+            if cb.count == 0 :
+                self.ignore(event)
+        cb.count = count
         self.watch(event, cb)
     async def cmd_ignore (self, *event:str) :
         """ignore specified events

@@ -57,9 +57,9 @@ class Simulator (object) :
         self.cb = {}
         self._ident = 0
     def connect (self, pattern, cb) :
-        ident = self._ident
         self._ident += 1
         self.cb[self._ident] = (pattern, cb)
+        return self._ident
     def disconnect (self, ident) :
         self.cb.pop(ident, None)
     async def ttc_event (self, name, *args) :
@@ -76,7 +76,7 @@ class Simulator (object) :
                 if a is NONE :
                     args[i] = None
             done = set()
-            for pat, fun in self.cb.values() :
+            for pat, fun in list(self.cb.values()) :
                 if fun in done :
                     continue
                 if match(event, pat) :