From 1760310123e6b86aecc545ae02b85ae8a7a8ab16 Mon Sep 17 00:00:00 2001
From: Max Kellermann <mk@cm4all.com>
Date: Tue, 23 Apr 2024 15:00:24 +0200
Subject: [PATCH] Revert "util/IntrusiveList: allow the last disposer to
 destroy the IntrusiveList"

This reverts commit 669cbcd25aec664c465907347601e48ab51c9aed
("util/IntrusiveList: allow the last disposer to destroy the
IntrusiveList").  It was bad because it could lead to off-by-one crash
bugs when the last item was removed inside the previous item's
disposer.

We need a different solution for the other crash bug that was fixed by
the reverted commit.
---
 src/util/IntrusiveList.hxx | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/src/util/IntrusiveList.hxx b/src/util/IntrusiveList.hxx
index f47ef266e..9a1a4eaef 100644
--- a/src/util/IntrusiveList.hxx
+++ b/src/util/IntrusiveList.hxx
@@ -293,20 +293,12 @@ public:
 
 	/**
 	 * Like clear(), but invoke a disposer function on each item.
+	 *
+	 * The disposer is not allowed to destruct the list.
 	 */
 	void clear_and_dispose(Disposer<value_type> auto disposer) noexcept {
-		bool is_empty = empty();
-
-		while (!is_empty) {
-			auto *item = &pop_front();
-
-			/* by checking empty() before invoking the
-			   disposer, it is possible for the disposer
-			   to destroy this IntrusiveList in the last
-			   call */
-			is_empty = empty();
-
-			disposer(item);
+		while (!empty()) {
+			disposer(&pop_front());
 		}
 	}