start() no longer raises an exception if Greenlet was already started. it also...

start() no longer raises an exception if Greenlet was already started. it also now does nothing if the greenlet already exited (previously it would schedule another switch)

gevent/greenlet.py

@@ -144,7 +144,7 @@ class Greenlet(greenlet):
         self._exception = _NONE
         loop = hub.loop
         self._notifier = loop.callback()
-        self._start_event = loop.callback()
+        self._start_event = None
 
     @property
     def loop(self):
@@ -152,11 +152,12 @@ class Greenlet(greenlet):
         return self.parent.loop
 
     def __nonzero__(self):
-        return self._start_event.pending or greenlet.__nonzero__(self)
+        return self._start_event is not None and self._exception is _NONE
 
     @property
     def started(self):
-        return self._start_event.pending or greenlet.__nonzero__(self)
+        # DEPRECATED
+        return self.__nonzero__()
 
     def ready(self):
         """Return true if and only if the greenlet has finished execution."""
@@ -215,7 +216,8 @@ class Greenlet(greenlet):
         a) cancel the event that will start it
         b) fire the notifications as if an exception was raised in a greenlet
         """
-        self._start_event.stop()
+        if self._start_event is not None:
+            self._start_event.stop()
         try:
             greenlet.throw(self, *args)
         finally:
@@ -237,14 +239,15 @@ class Greenlet(greenlet):
 
     def start(self):
         """Schedule the greenlet to run in this loop iteration"""
-        assert not self.started, 'Greenlet already started'
-        self._start_event.start(self.switch)
+        if self._start_event is None:
+            self._start_event = self.parent.loop.callback()
+            self._start_event.start(self.switch)
 
     def start_later(self, seconds):
         """Schedule the greenlet to run in the future loop iteration *seconds* later"""
-        assert not self.started, 'Greenlet already started'
-        self._start_event = self.parent.loop.timer(seconds)
-        self._start_event.start(self.switch)
+        if self._start_event is None:
+            self._start_event = self.parent.loop.timer(seconds)
+            self._start_event.start(self.switch)
 
     @classmethod
     def spawn(cls, *args, **kwargs):
@@ -294,7 +297,8 @@ class Greenlet(greenlet):
 
         `Changed in version 0.13.0:` *block* is now ``True`` by default.
         """
-        self._start_event.stop()
+        if self._start_event is not None:
+            self._start_event.stop()
         if not self.dead:
             waiter = Waiter()
             self.parent.loop.run_callback(_kill, self, exception, waiter)