max / makenotwork

Fix DashMap deadlock in SSE connection guard drop The SseConnectionGuard::drop held a DashMap read lock (via .get()) while calling .remove() on the same shard, which requires a write lock. This deadlocked the entire server whenever a SyncKit SSE connection disconnected. Fix: extract the needed value via .map() to drop the read guard before calling .remove(). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Max J. <87768334+MaxJMath@users.noreply.github.com> · 2026-05-11 18:22 UTC

Commit: f1b410b08ba0c397a3d0da0b1e7276e927bd5818

Parent: ea0e960

1 file changed, +17 insertions, -10 deletions

M server/src/routes/synckit/subscribe.rs +17 -10

			@@ -35,19 +35,26 @@ struct SseConnectionGuard {
35	35
36	36		impl Drop for SseConnectionGuard {
37	37		fn drop(&mut self) {
38		-	if let Some(counter) = self.sse_connections.get(&self.user_id) {
	38	+	// Decrement connection counter, then remove entry if it hit zero.
	39	+	// Must drop the read guard before calling remove() to avoid deadlocking
	40	+	// on the same DashMap shard.
	41	+	let should_remove_connection = self.sse_connections.get(&self.user_id).map(\|counter\| {
39	42		let prev = counter.value().fetch_sub(1, Ordering::AcqRel);
40		-	// If this was the last connection for this user, remove the entry
41		-	if prev <= 1 {
42		-	self.sse_connections.remove(&self.user_id);
43		-	}
	43	+	prev <= 1
	44	+	}).unwrap_or(false);
	45	+
	46	+	if should_remove_connection {
	47	+	self.sse_connections.remove(&self.user_id);
44	48		}
45		-	// Prune sync_notify channel if no receivers remain
	49	+
	50	+	// Prune sync_notify channel if no receivers remain.
	51	+	// Same pattern: read first, drop guard, then remove.
46	52		let key = (self.app_id, self.user_id);
47		-	if let Some(entry) = self.sync_notify.get(&key)
48		-	&& entry.value().receiver_count() == 0
49		-	{
50		-	drop(entry);
	53	+	let should_remove_notify = self.sync_notify.get(&key)
	54	+	.map(\|entry\| entry.value().receiver_count() == 0)
	55	+	.unwrap_or(false);
	56	+
	57	+	if should_remove_notify {
51	58		self.sync_notify.remove(&key);
52	59		}
53	60		}