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Fix the logcontext handling in the cache wrappers (#2077)

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The cache wrappers had a habit of leaking the logcontext into the reactor while
the lookup function was running, and then not restoring it correctly when the
lookup function had completed. It's all the fault of
`preserve_context_over_{fn,deferred}` which are basically a bit broken.
This commit is contained in:
Richard van der Hoff 2017-03-30 13:22:24 +01:00 • committed by GitHub
parent 30348c924c
commit f9b4bb05e0
4 changed files with 136 additions and 19 deletions
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30
synapse/util/caches/descriptors.py
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@ -15,12 +15,9 @@
import logging
from synapse.util.async import ObservableDeferred
from synapse.util import unwrapFirstError
from synapse.util import unwrapFirstError, logcontext
from synapse.util.caches.lrucache import LruCache
from synapse.util.caches.treecache import TreeCache, iterate_tree_cache_entry
from synapse.util.logcontext import (
PreserveLoggingContext, preserve_context_over_deferred, preserve_context_over_fn
)
from . import DEBUG_CACHES, register_cache
@ -328,11 +325,9 @@ class CacheDescriptor(_CacheDescriptorBase):
defer.returnValue(cached_result)
observer.addCallback(check_result)
return preserve_context_over_deferred(observer)
except KeyError:
ret = defer.maybeDeferred(
preserve_context_over_fn,
self.function_to_call,
logcontext.preserve_fn(self.function_to_call),
obj, *args, **kwargs
)
@ -342,10 +337,11 @@ class CacheDescriptor(_CacheDescriptorBase):
ret.addErrback(onErr)
ret = ObservableDeferred(ret, consumeErrors=True)
cache.set(cache_key, ret, callback=invalidate_callback)
result_d = ObservableDeferred(ret, consumeErrors=True)
cache.set(cache_key, result_d, callback=invalidate_callback)
observer = result_d.observe()
return preserve_context_over_deferred(ret.observe())
return logcontext.make_deferred_yieldable(observer)
wrapped.invalidate = cache.invalidate
wrapped.invalidate_all = cache.invalidate_all
@ -362,7 +358,11 @@ class CacheListDescriptor(_CacheDescriptorBase):
"""Wraps an existing cache to support bulk fetching of keys.
Given a list of keys it looks in the cache to find any hits, then passes
the list of missing keys to the wrapped fucntion.
the list of missing keys to the wrapped function.
Once wrapped, the function returns either a Deferred which resolves to
the list of results, or (if all results were cached), just the list of
results.
"""
def __init__(self, orig, cached_method_name, list_name, num_args=None,
@ -433,8 +433,7 @@ class CacheListDescriptor(_CacheDescriptorBase):
args_to_call[self.list_name] = missing
ret_d = defer.maybeDeferred(
preserve_context_over_fn,
self.function_to_call,
logcontext.preserve_fn(self.function_to_call),
**args_to_call
)
@ -443,8 +442,7 @@ class CacheListDescriptor(_CacheDescriptorBase):
# We need to create deferreds for each arg in the list so that
# we can insert the new deferred into the cache.
for arg in missing:
with PreserveLoggingContext():
observer = ret_d.observe()
observer = ret_d.observe()
observer.addCallback(lambda r, arg: r.get(arg, None), arg)
observer = ObservableDeferred(observer)
@ -471,7 +469,7 @@ class CacheListDescriptor(_CacheDescriptorBase):
results.update(res)
return results
return preserve_context_over_deferred(defer.gatherResults(
return logcontext.make_deferred_yieldable(defer.gatherResults(
cached_defers.values(),
consumeErrors=True,
).addCallback(update_results_dict).addErrback(