Added Signal._cleanup_bookeeping() to prune stale bookkeeping on demand.

CHANGES

@@ -7,6 +7,8 @@ Version 1.4dev
 
 - Additional bookkeeping cleanup for non-ANY connections at disconnect
   time.
+- Added Signal._cleanup_bookeeping() to prune stale bookkeeping on
+  demand
 
 Version 1.3
 -----------

blinker/base.py

@@ -348,6 +348,32 @@ def _cleanup_sender(self, sender_ref):
         for receiver_id in self._by_sender.pop(sender_id, ()):
             self._by_receiver[receiver_id].discard(sender_id)
 
+    def _cleanup_bookkeeping(self):
+        """Prune unused sender/receiver bookeeping. Not threadsafe.
+
+        Connecting & disconnecting leave behind a small amount of bookeeping
+        for the receiver and sender values. Typical workloads using Blinker,
+        for example in most web apps, Flask, CLI scripts, etc., are not
+        adversely affected by this bookkeeping.
+
+        With a long-running Python process performing dynamic signal routing
+        with high volume- e.g. connecting to function closures, "senders" are
+        all unique object instances, and doing all of this over and over- you
+        may see memory usage will grow due to extraneous bookeeping. (An empty
+        set() for each stale sender/receiver pair.)
+
+        This method will prune that bookeeping away, with the caveat that such
+        pruning is not threadsafe. The risk is that cleanup of a fully
+        disconnected receiver/sender pair occurs while another thread is
+        connecting that same pair. If you are in the highly dynamic, unique
+        receiver/sender situation that has lead you to this method, that
+        failure mode is perhaps not a big deal for you.
+        """
+        for mapping in (self._by_sender, self._by_receiver):
+            for _id, bucket in list(mapping.items()):
+                if not bucket:
+                    mapping.pop(_id, None)
+
     def _clear_state(self):
         """Throw away all signal state.  Useful for unit tests."""
         self._weak_senders.clear()

tests/test_signals.py

@@ -211,6 +211,10 @@ class Sender(object):
     assert senders() == (1, 0)
     assert receivers() == (2, 0)
 
+    sig._cleanup_bookkeeping()
+    assert senders() == (0, 0)
+    assert receivers() == (0, 0)
+
 
 def test_meta_connect_failure():
     def meta_received(sender, **kw):