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Fix stackoverflow and logcontexts from linearizer

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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.
This commit is contained in:
Richard van der Hoff 2017-10-11 15:05:05 +01:00
parent 4d24becf7f
commit 4fad8efbfb
2 changed files with 46 additions and 6 deletions
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24
synapse/util/async.py
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@ -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)