Raise warning when using async Sentry transport.

CHANGES.md

@@ -1,7 +1,7 @@
 ### 0.4.6
 (not released yet)
 
-- ...
+- Fix where Sentry logging did not reliably work in the worker process.
 
 
 ### 0.4.5

rq/contrib/sentry.py

@@ -1,12 +1,24 @@
 # -*- coding: utf-8 -*-
 from __future__ import (absolute_import, division, print_function,
                         unicode_literals)
+import warnings
 
 
 def register_sentry(client, worker):
     """Given a Raven client and an RQ worker, registers exception handlers
     with the worker so exceptions are logged to Sentry.
     """
+    def uses_supported_transport(url):
+        supported_transports = set(['sync+', 'requests+'])
+        return any(url.startswith(prefix) for prefix in supported_transports)
+
+    if not any(uses_supported_transport(s) for s in client.servers):
+        msg = ('Sentry error delivery is known to be unreliable when not '
+               'delivered synchronously from RQ workers.  You are encouraged '
+               'to change your DSN to use the sync+ or requests+ transport '
+               'prefix.')
+        warnings.warn(msg, UserWarning, stacklevel=2)
+
     def send_to_sentry(job, *exc_info):
         client.captureException(
             exc_info=exc_info,