From 05d9d61a655455b3729e5d13097f151ce7248e02 Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Wed, 21 May 2025 12:40:25 +1000
Subject: [PATCH] Check for changing deferred action counts

---
 deferrwl.go | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/deferrwl.go b/deferrwl.go
index bf95be24..0f1b3a54 100644
--- a/deferrwl.go
+++ b/deferrwl.go
@@ -1,6 +1,10 @@
 package torrent
 
-import "github.com/anacrolix/sync"
+import (
+	"fmt"
+
+	"github.com/anacrolix/sync"
+)
 
 // Runs deferred actions on Unlock. Note that actions are assumed to be the results of changes that
 // would only occur with a write lock at present. The race detector should catch instances of defers
@@ -15,12 +19,15 @@ func (me *lockWithDeferreds) Lock() {
 }
 
 func (me *lockWithDeferreds) Unlock() {
-	unlockActions := me.unlockActions
-	for i := 0; i < len(unlockActions); i += 1 {
-		unlockActions[i]()
+	defer me.internal.Unlock()
+	startLen := len(me.unlockActions)
+	for i := range startLen {
+		me.unlockActions[i]()
+	}
+	if len(me.unlockActions) != startLen {
+		panic(fmt.Sprintf("num deferred changed while running: %v -> %v", startLen, len(me.unlockActions)))
 	}
-	me.unlockActions = unlockActions[:0]
-	me.internal.Unlock()
+	me.unlockActions = me.unlockActions[:0]
 }
 
 func (me *lockWithDeferreds) RLock() {
-- 
2.51.0