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Fix race condition in ExpireAfter when items are removed before expiration fires #1076

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Fix race condition in ExpireAfter when items are removed before expiration fires #1076

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19 changes: 13 additions & 6 deletions src/DynamicData/Cache/Internal/ExpireAfter.ForSource.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -161,11 +161,18 @@ private void OnEditingSource(ISourceUpdater<TObject, TKey> updater)
{
_expirationDueTimesByKey.Remove(proposedExpiration.Key);

_removedItemsBuffer.Add(new(
key: proposedExpiration.Key,
value: updater.Lookup(proposedExpiration.Key).Value));

updater.RemoveKey(proposedExpiration.Key);
// The item may have been removed or updated by another thread between when
// this expiration was scheduled and when it fired. Check that the item is
// still present and still has an expiration before removing it.
var lookup = updater.Lookup(proposedExpiration.Key);
if (lookup.HasValue && _timeSelector.Invoke(lookup.Value) is not null)
{
_removedItemsBuffer.Add(new(
key: proposedExpiration.Key,
value: lookup.Value));

updater.RemoveKey(proposedExpiration.Key);
}
Comment on lines +168 to +175
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Copilot AI Apr 10, 2026

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_timeSelector is user-provided and can throw. Calling _timeSelector.Invoke(lookup.Value) inside the scheduled expiration-management path (OnEditingSource via ManageExpirations) is currently unguarded (no try/catch here or around _source.Edit(_onEditingSource)), so an exception would escape the scheduler callback instead of being propagated via _observer.OnError (as OnSourceNext does). Consider either avoiding timeSelector evaluation here (rely on internal expiration state), or wrapping the invocation/removal block to cancel further scheduling and forward the error to _observer.OnError consistently.

Suggested change
if (lookup.HasValue && _timeSelector.Invoke(lookup.Value) is not null)
{
_removedItemsBuffer.Add(new(
key: proposedExpiration.Key,
value: lookup.Value));
updater.RemoveKey(proposedExpiration.Key);
}
try
{
if (lookup.HasValue && _timeSelector.Invoke(lookup.Value) is not null)
{
_removedItemsBuffer.Add(new(
key: proposedExpiration.Key,
value: lookup.Value));
updater.RemoveKey(proposedExpiration.Key);
}
}
catch (Exception error)
{
_observer.OnError(error);
return;
}

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}
}
_proposedExpirationsQueue.RemoveRange(0, proposedExpirationIndex);
Expand Down Expand Up @@ -273,7 +280,7 @@ private void OnSourceNext(IChangeSet<TObject, TKey> changes)
{
if (_timeSelector.Invoke(change.Current) is { } expireAfter)
{
haveExpirationsChanged = TrySetExpiration(
haveExpirationsChanged |= TrySetExpiration(
key: change.Key,
dueTime: now + expireAfter);
}
Expand Down
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