From 5ca7630c8cdc660b1f796fe55102e354c1f6a26a Mon Sep 17 00:00:00 2001
From: Konstantin Nazarov <mail@knazarov.com>
Date: Sat, 20 Jul 2024 22:56:45 +0100
Subject: [PATCH] Make a simple gc root actually work

---
 src/arena.hpp | 21 ++++++++++-----------
 src/vli.cpp   |  6 ++++++
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/src/arena.hpp b/src/arena.hpp
index c8b9ed4..6e9f66d 100644
--- a/src/arena.hpp
+++ b/src/arena.hpp
@@ -11,6 +11,7 @@ class GcRootList;
 
 class GcRootBase {
  public:
+  GcRootBase() : _ptr(0), _node(0){};
   GcRootBase(PodObject* ptr, GcRootList* node);
 
   ~GcRootBase();
@@ -55,8 +56,8 @@ class GcRootList {
   void remove() {
     _prev = 0;
     _next = 0;
-    _prev->_next = _next;
-    _next->_prev = _prev;
+    if (_prev) _prev->_next = _next;
+    if (_next) _next->_prev = _prev;
   }
 
   void update(GcRootBase* root) { _root = root; }
@@ -114,26 +115,22 @@ class Arena {
 };
 
 template <uint64_t size>
-class StaticArenaHeap {
+class StaticArenaHeap : public ArenaHeap {
  public:
-  StaticArenaHeap() : _heap(_buf, heapsize) {}
-
-  ArenaHeap* get() { return &_heap; }
+  StaticArenaHeap() : ArenaHeap(_buf, heapsize) {}
 
  private:
   static const uint64_t heapsize = size - sizeof(ArenaHeap);
-  ArenaHeap _heap;
   uint8_t _buf[heapsize]{0};
 };
 
 template <uint64_t size>
-class StaticArena {
+class StaticArena : public Arena {
  public:
-  StaticArena() : _arena(_heaps[0].get(), _heaps[1].get()) {}
+  StaticArena() : Arena(&_heaps[0], &_heaps[1]) {}
 
  private:
   StaticArenaHeap<(size - sizeof(Arena)) / 2> _heaps[2];
-  Arena _arena;
 };
 
 template <class T>
@@ -141,11 +138,13 @@ template <class T>
 Result<GcRoot<T>> GcRoot<T>::create(T* ptr, Arena& arena) {
   auto lst = TRY(arena.alloc<GcRootList>());
   arena.add_root(lst);
-  return GcRoot<T>(ptr, lst);
+  return std::move(GcRoot<T>(ptr, lst));
 }
 
 template <class T>
   requires std::derived_from<T, PodObject>
 GcRoot<T>::GcRoot(GcRoot<T>&& rhs) {
   rhs._node->update(this);
+  _ptr = rhs._ptr;
+  _node = rhs._node;
 }
diff --git a/src/vli.cpp b/src/vli.cpp
index 3d702e2..a223145 100644
--- a/src/vli.cpp
+++ b/src/vli.cpp
@@ -1,10 +1,12 @@
 #include <iostream>
 
+#include "arena.hpp"
 #include "common.hpp"
 
 StaticArena<64 * 1024 * 1024> arena;
 
 int main() {
+  /*
   Value val;
   std::cout << sizeof(val) << "\n";
   std::cout << int(val->tag()) << "\n";
@@ -14,6 +16,10 @@ int main() {
   std::cout << sizeof(val) << "\n";
   std::cout << int(val->tag()) << "\n";
   std::cout << int(((Int64&)*val).value()) << "\n";
+  */
+
+  auto lst = DIEIF(arena.alloc<PodPair>());
+  auto root = DIEIF(MkGcRoot(lst, arena));
 
   return 0;
 }