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authorRichard van der Hoff <richard@matrix.org>2017-10-11 15:05:05 +0100
committerRichard van der Hoff <richard@matrix.org>2017-10-11 15:05:05 +0100
commit4fad8efbfb1726c72bdd7cbbacc894b8701efec3 (patch)
tree355ebe6a112915c9028d7ca6296f493cff12320a /synapse
parentMerge pull request #2517 from matrix-org/rav/fed_server_refactor (diff)
downloadsynapse-4fad8efbfb1726c72bdd7cbbacc894b8701efec3.tar.xz
Fix stackoverflow and logcontexts from linearizer
1. make it not blow out the stack when there are more than 50 things waiting
   for a lock. Fixes https://github.com/matrix-org/synapse/issues/2505.

2. Make it not mess up the log contexts.
Diffstat (limited to 'synapse')
-rw-r--r--synapse/util/async.py24
1 files changed, 22 insertions, 2 deletions
diff --git a/synapse/util/async.py b/synapse/util/async.py
index bb252f75d7..0fd5b42523 100644
--- a/synapse/util/async.py
+++ b/synapse/util/async.py
@@ -203,7 +203,26 @@ class Linearizer(object):
             except:
                 logger.exception("Unexpected exception in Linearizer")
 
-        logger.info("Acquired linearizer lock %r for key %r", self.name, key)
+            logger.info("Acquired linearizer lock %r for key %r", self.name,
+                        key)
+
+            # if the code holding the lock completes synchronously, then it
+            # will recursively run the next claimant on the list. That can
+            # relatively rapidly lead to stack exhaustion. This is essentially
+            # the same problem as http://twistedmatrix.com/trac/ticket/9304.
+            #
+            # In order to break the cycle, we add a cheeky sleep(0) here to
+            # ensure that we fall back to the reactor between each iteration.
+            #
+            # (There's no particular need for it to happen before we return
+            # the context manager, but it needs to happen while we hold the
+            # lock, and the context manager's exit code must be synchronous,
+            # so actually this is the only sensible place.
+            yield run_on_reactor()
+
+        else:
+            logger.info("Acquired uncontended linearizer lock %r for key %r",
+                        self.name, key)
 
         @contextmanager
         def _ctx_manager():
@@ -211,7 +230,8 @@ class Linearizer(object):
                 yield
             finally:
                 logger.info("Releasing linearizer lock %r for key %r", self.name, key)
-                new_defer.callback(None)
+                with PreserveLoggingContext():
+                    new_defer.callback(None)
                 current_d = self.key_to_defer.get(key)
                 if current_d is new_defer:
                     self.key_to_defer.pop(key, None)