blinker.patch

--- /home/vagrant/python/lib/python2.7/site-packages/blinker/base.py	2017-05-12 22:29:27.020638000 +0000
+++ base.py	2017-05-12 22:29:02.000000000 +0000
@@ -21,6 +21,13 @@
     symbol,
     )
 
+import logging;
+FORMAT = '%(asctime)s %(message)s'
+
+log = logging.getLogger()
+handler = logging.FileHandler("./ddtrace_blinker.log")
+handler.setFormatter(logging.Formatter(FORMAT))
+log.addHandler(handler)
 
 ANY = symbol('ANY')
 ANY.__doc__ = 'Token for "any sender".'
@@ -108,6 +115,7 @@
           is garbage collected.  Defaults to True.
 
         """
+        log.warn("Connected %s %s %s", receiver, sender, weak)
         receiver_id = hashable_identity(receiver)
         if weak:
             receiver_ref = reference(receiver, self._cleanup_receiver)
@@ -253,6 +261,7 @@
         # Using '*sender' rather than 'sender=None' allows 'sender' to be
         # used as a keyword argument- i.e. it's an invisible name in the
         # function signature.
+        log.warn("Sent %s %s", sender, kwargs)
         if len(sender) == 0:
             sender = None
         elif len(sender) > 1:
@@ -313,6 +322,7 @@
           to disconnect from all senders.  Defaults to ``ANY``.
 
         """
+        log.warn("Disconnected %s %s", receiver, sender)
         if sender is ANY:
             sender_id = ANY_ID
         else:
@@ -327,6 +337,7 @@
                                             sender=sender)
 
     def _disconnect(self, receiver_id, sender_id):
+        log.warn("_disconnected %s %s", receiver_id, sender_id)
         if sender_id == ANY_ID:
             if self._by_receiver.pop(receiver_id, False):
                 for bucket in self._by_sender.values():
@@ -341,6 +352,7 @@
 
     def _cleanup_sender(self, sender_ref):
         """Disconnect all receivers from a sender."""
+        log.warn("_cleanup_sender %s %s", sender_ref)
         sender_id = sender_ref.sender_id
         assert sender_id != ANY_ID
         self._weak_senders.pop(sender_id, None)

apply with

$ wget -O blinker.patch https://gist.githubusercontent.com/talwai/c3a000edda6db8312210c74caaded261/raw/7f92eec60ed1b52eeff32fc863d774778afc6c22/blinker.patch

$ patch /path/to/site-packages/blinker/base.py blinker.patch

For a traced flask app using blinker, this will output all signal operations into $CWD/ddtrace_blinker.log . Hopefully this will let us see if any receivers get disconnected or unintentionally lost to garbage collection.