Semaphore: avoid copying list of links; rawlink() no longer schedules notification

Avoid copying list of links by maintaining a 'dirty' flag that causes
_notify_links to restart iteration. This makes sure that we don't miss
a recently added link because notification is already in progress.

It is possible to notify the same links (that did not remove themselvers)
more than once, but it's better than not notifying some links at all.

rawlink() no longer schedules notification immediatelly if needed, because
there seem to be utility in such behaviour.

gevent/coros.py

@@ -34,18 +34,22 @@ class Semaphore(object):
     def release(self):
         self.counter += 1
         if self._links and self.counter > 0 and not self._notifier.active:
-            self._notifier.start(self._notify_links, list(self._links))
-            # XXX so what if there was another release() with different self._links? it would be ignored then?
-
-    def _notify_links(self, links):
-        for link in links:
-            if self.counter <= 0:
-                return
-            if link in self._links:
+            self._notifier.start(self._notify_links)
+
+    def _notify_links(self):
+        while True:
+            self._dirty = False
+            for link in self._links:
+                if self.counter <= 0:
+                    return
                 try:
                     link(self)
                 except:
                     self.hub.handle_error((link, self), *sys.exc_info())
+                if self._dirty:
+                    break
+            if not self._dirty:
+                return
 
     def rawlink(self, callback):
         """Register a callback to call when a counter is more than zero.
@@ -56,13 +60,13 @@ class Semaphore(object):
         if not callable(callback):
             raise TypeError('Expected callable: %r' % (callback, ))
         self._links.append(callback)
-        if self.counter > 0 and not self._notifier.active:
-            self._notifier.start(self._notify_links, list(self._links))
+        self._dirty = True
 
     def unlink(self, callback):
         """Remove the callback set by :meth:`rawlink`"""
         try:
             self._links.remove(callback)
+            self._dirty = True
         except ValueError:
             pass