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Fix a bug which could cause incorrect 'cyclic dependency' error. (#7178) 

If there was an exception setting up one of the attributes of the Homeserver
god object, then future attempts to fetch that attribute would raise a
confusing "Cyclic dependency" error. Let's make sure that we clear the
`building` flag so that we just get the original exception.

Ref: #7169
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Richard van der Hoff 2020-03-31 13:09:16 +01:00 committed by GitHub
parent 7966a1cde9
commit 62a7289133
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2 changed files with 11 additions and 12 deletions
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1
changelog.d/7178.bugfix Normal file
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@ -0,0 +1 @@
Fix a bug which could cause incorrect 'cyclic dependency' error.

22
synapse/server.py
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@ -583,24 +583,22 @@ def _make_dependency_method(depname):
try: try:
builder = getattr(hs, "build_%s" % (depname)) builder = getattr(hs, "build_%s" % (depname))
except AttributeError: except AttributeError:
builder = None raise NotImplementedError(
"%s has no %s nor a builder for it" % (type(hs).__name__, depname)
)
if builder: # Prevent cyclic dependencies from deadlocking
# Prevent cyclic dependencies from deadlocking if depname in hs._building:
if depname in hs._building: raise ValueError("Cyclic dependency while building %s" % (depname,))
raise ValueError("Cyclic dependency while building %s" % (depname,))
hs._building[depname] = 1
hs._building[depname] = 1
try:
dep = builder() dep = builder()
setattr(hs, depname, dep) setattr(hs, depname, dep)
finally:
del hs._building[depname] del hs._building[depname]
return dep return dep
raise NotImplementedError(
"%s has no %s nor a builder for it" % (type(hs).__name__, depname)
)
setattr(HomeServer, "get_%s" % (depname), _get) setattr(HomeServer, "get_%s" % (depname), _get)