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Be careful with logcontext in DeferredEvent #19142

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Be careful with logcontext in DeferredEvent #19142

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Be careful with logcontext in `DeferredEvent`
MadLittleMods Nov 4, 2025
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MadLittleMods Nov 4, 2025
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1 change: 1 addition & 0 deletions changelog.d/19142.misc
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@@ -0,0 +1 @@
Respect logcontext in `DeferredEvent`.
3 changes: 2 additions & 1 deletion synapse/util/async_helpers.py
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Expand Up @@ -1029,7 +1029,8 @@ def __init__(self, clock: Clock) -> None:

def set(self) -> None:
if not self._deferred.called:
self._deferred.callback(None)
with PreserveLoggingContext():
self._deferred.callback(None)
Comment on lines +1032 to +1033
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@MadLittleMods MadLittleMods Nov 4, 2025

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This is the main fix!

See the Deferred callbacks section of our logcontext docs for more info (specifically using solution 2).

Heads-up, I wrote the docs too so it's my assumptions/understanding all the way down. Apply your own scrutiny.

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@MadLittleMods MadLittleMods Nov 4, 2025

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This usage is actually probably fine given you can't get a handle to the raw deferred and add some callbacks to the chain that could cause the logcontext to change.

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@MadLittleMods MadLittleMods Nov 5, 2025

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This was actually a problem, see #19146 (comment) for an explanation


def clear(self) -> None:
if self._deferred.called:
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