From 639cd07d6d4e22e3413349bbd3bfb33db37a8d2f Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 7 Apr 2016 14:24:12 +0100
Subject: [PATCH] Add comment
---
synapse/util/async.py | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/synapse/util/async.py b/synapse/util/async.py
index 408c86be91..14a3dfd43f 100644
--- a/synapse/util/async.py
+++ b/synapse/util/async.py
@@ -164,6 +164,14 @@ class Linearizer(object):
@defer.inlineCallbacks
def queue(self, key):
+ # If there is already a deferred in the queue, we pull it out so that
+ # we can wait on it later.
+ # Then we replace it with a deferred that we resolve *after* the
+ # context manager has exited.
+ # We only return the context manager after the previous deferred has
+ # resolved.
+ # This all has the net effect of creating a chain of deferreds that
+ # wait for the previous deferred before starting their work.
current_defer = self.key_to_defer.get(key)
new_defer = defer.Deferred()
--
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