From 1048f23680ece42be173d8e42c4cb80738a9c411 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Wed, 24 Feb 2021 20:28:47 +0100
Subject: [PATCH] util/IntrusiveList: add hook class SafeLinkIntrusiveListHook

Similar to boost::intrusive::safe_link.
---
 src/util/IntrusiveList.hxx | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/src/util/IntrusiveList.hxx b/src/util/IntrusiveList.hxx
index 4f88ac626..19b9a5b11 100644
--- a/src/util/IntrusiveList.hxx
+++ b/src/util/IntrusiveList.hxx
@@ -65,21 +65,15 @@ private:
 };
 
 /**
- * A variant of #IntrusiveListHook which auto-unlinks itself from the
- * list upon destruction.  As a side effect, it has an is_linked()
- * method.
+ * A variant of #IntrusiveListHook which keeps track of whether it is
+ * currently in a list.
  */
-class AutoUnlinkIntrusiveListHook : public IntrusiveListHook {
+class SafeLinkIntrusiveListHook : public IntrusiveListHook {
 public:
-	AutoUnlinkIntrusiveListHook() noexcept {
+	SafeLinkIntrusiveListHook() noexcept {
 		siblings.next = nullptr;
 	}
 
-	~AutoUnlinkIntrusiveListHook() noexcept {
-		if (is_linked())
-			unlink();
-	}
-
 	void unlink() noexcept {
 		IntrusiveListHook::unlink();
 		siblings.next = nullptr;
@@ -90,6 +84,19 @@ public:
 	}
 };
 
+/**
+ * A variant of #IntrusiveListHook which auto-unlinks itself from the
+ * list upon destruction.  As a side effect, it has an is_linked()
+ * method.
+ */
+class AutoUnlinkIntrusiveListHook : public SafeLinkIntrusiveListHook {
+public:
+	~AutoUnlinkIntrusiveListHook() noexcept {
+		if (is_linked())
+			unlink();
+	}
+};
+
 template<typename T>
 class IntrusiveList {
 	IntrusiveListNode head{&head, &head};
@@ -140,7 +147,7 @@ public:
 	}
 
 	~IntrusiveList() noexcept {
-		if constexpr (std::is_base_of<AutoUnlinkIntrusiveListHook, T>::value)
+		if constexpr (std::is_base_of<SafeLinkIntrusiveListHook, T>::value)
 			clear();
 	}
 
@@ -151,8 +158,8 @@ public:
 	}
 
 	void clear() noexcept {
-		if constexpr (std::is_base_of<AutoUnlinkIntrusiveListHook, T>::value) {
-			/* for AutoUnlinkIntrusiveListHook, we need to
+		if constexpr (std::is_base_of<SafeLinkIntrusiveListHook, T>::value) {
+			/* for SafeLinkIntrusiveListHook, we need to
 			   remove each item manually, or else its
 			   is_linked() method will not work */
 			while (!empty())