From 4114118a9ed01f289c0694b9053af63191e6b987 Mon Sep 17 00:00:00 2001
From: Kegan Dougal <kegan@matrix.org>
Date: Thu, 21 Sep 2023 17:15:23 +0100
Subject: [PATCH] Reduce mutex contention on callbacks

---
 sync2/poller.go | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/sync2/poller.go b/sync2/poller.go
index 85d611a0..4902bf69 100644
--- a/sync2/poller.go
+++ b/sync2/poller.go
@@ -222,19 +222,25 @@ func (h *PollerMap) DeviceIDs(userID string) []string {
 
 func (h *PollerMap) ExpirePollers(pids []PollerID) int {
 	h.pollerMu.Lock()
-	defer h.pollerMu.Unlock()
 	numTerminated := 0
+	var pollersToTerminate []*poller
 	for _, pid := range pids {
 		p, ok := h.Pollers[pid]
 		if !ok || p.terminated.Load() {
 			continue
 		}
+		pollersToTerminate = append(pollersToTerminate, p)
+	}
+	h.pollerMu.Unlock()
+	// now terminate the pollers.
+	for _, p := range pollersToTerminate {
 		p.Terminate()
 		// Ensure that we won't recreate this poller on startup. If it reappears later,
 		// we'll make another EnsurePolling call which will recreate the poller.
 		h.callbacks.OnExpiredToken(context.Background(), hashToken(p.accessToken), p.userID, p.deviceID)
 		numTerminated++
 	}
+
 	return numTerminated
 }