Implement locks using create_observer for fetching media and server keys

synapse/crypto/keyring.py

@@ -24,6 +24,8 @@ from synapse.api.errors import SynapseError, Codes
 
 from synapse.util.retryutils import get_retry_limiter
 
+from synapse.util.async import create_observer
+
 from OpenSSL import crypto
 
 import logging
@@ -38,6 +40,8 @@ class Keyring(object):
         self.clock = hs.get_clock()
         self.hs = hs
 
+        self.key_downloads = {}
+
     @defer.inlineCallbacks
     def verify_json_for_server(self, server_name, json_object):
         logger.debug("Verifying for %s", server_name)
@@ -97,6 +101,8 @@ class Keyring(object):
             defer.returnValue(cached[0])
             return
 
+        @defer.inlineCallbacks
+        def fetch_keys():
             # Try to fetch the key from the remote server.
 
             limiter = yield get_retry_limiter(
@@ -170,3 +176,17 @@ class Keyring(object):
                     return
 
             raise ValueError("No verification key found for given key ids")
+
+        download = self.key_downloads.get(server_name)
+
+        if download is None:
+            download = fetch_keys()
+            self.key_downloads[server_name] = download
+
+            @download.addBoth
+            def callback(ret):
+                del self.key_downloads[server_name]
+                return ret
+
+        r = yield create_observer(download)
+        defer.returnValue(r)

synapse/rest/media/v1/base_resource.py

@@ -25,6 +25,8 @@ from twisted.internet import defer
 from twisted.web.resource import Resource
 from twisted.protocols.basic import FileSender
 
+from synapse.util.async import create_observer
+
 import os
 
 import logging
@@ -87,7 +89,7 @@ class BaseMediaResource(Resource):
             def callback(media_info):
                 del self.downloads[key]
                 return media_info
-        return download
+        return create_observer(download)
 
     @defer.inlineCallbacks
     def _get_remote_media_impl(self, server_name, media_id):