From e0f0bb0713c45de883456f50a14558352f06cec9 Mon Sep 17 00:00:00 2001
From: Warwick <warwick.l.e.new@gmail.com>
Date: Mon, 24 Nov 2025 11:18:19 +0000
Subject: [PATCH] Remove dangling pointers on arena parents

---
 src/arena_allocator.c | 12 +++++++++---
 src/arena_allocator.h |  3 +--
 src/main.c            |  4 ++++
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/arena_allocator.c b/src/arena_allocator.c
index 86057df..d11a6e3 100644
--- a/src/arena_allocator.c
+++ b/src/arena_allocator.c
@@ -26,7 +26,7 @@ Arena *arena_init(Arena *parent, size_t capacity) {
   if (parent != NULL) {
     // Allocate new arena in parent to reduce likelyhood of loss
     Arena *current_arena = arena_alloc(parent, sizeof(Arena));
-    *current_arena = (Arena){.is_root = false,
+    *current_arena = (Arena){.parent = parent,
                              .begin = region,
                              .end = region,
                              .child = NULL,
@@ -46,7 +46,7 @@ Arena *arena_init(Arena *parent, size_t capacity) {
 
   // Create root of arena tree
   Arena *arena = malloc(sizeof(Arena));
-  *arena = (Arena){.is_root = true,
+  *arena = (Arena){.parent = NULL,
                    .begin = region,
                    .end = region,
                    .child = NULL,
@@ -76,9 +76,15 @@ void arena_deinit(Arena *arena) {
 
   arena->begin = NULL;
   arena->end = NULL;
-  if (arena->is_root) {
+
+  // If we're the tree root free us from malloc
+  if (arena->parent == NULL) {
     free(arena);
+    return;
   }
+
+  // Now that we have no descendants tell our parent of our death
+  arena->parent->child = arena->sibling;
 }
 
 void *arena_alloc(Arena *arena, size_t size) {
diff --git a/src/arena_allocator.h b/src/arena_allocator.h
index 6dbe772..0c48a10 100644
--- a/src/arena_allocator.h
+++ b/src/arena_allocator.h
@@ -1,6 +1,5 @@
 #pragma once
 
-#include <stdbool.h>
 #include <stddef.h>
 
 typedef struct Region_s Region;
@@ -13,7 +12,7 @@ struct Region_s {
 
 typedef struct Arena_s Arena;
 struct Arena_s {
-  bool is_root;
+  Arena *parent;
   Arena *child;
   Arena *sibling;
   Region *begin;
diff --git a/src/main.c b/src/main.c
index a0404d2..5dae4d4 100644
--- a/src/main.c
+++ b/src/main.c
@@ -25,8 +25,12 @@ int main(int argc, char *argv[]) {
   Arena *child_arena = arena_init(global_arena, 0);
   Arena *sibling_arena = arena_init(global_arena, 0);
   Arena *grandchild_arena = arena_init(child_arena, 0);
+  Arena *greatgrandchild_arena = arena_init(grandchild_arena, 0);
+  Arena *greategreatgrandchild_arena = arena_init(greatgrandchild_arena, 0);
 
   printf("deinit test\n");
+  arena_deinit(greatgrandchild_arena);
+
   arena_deinit(global_arena);
 
   printf("tests complete\n");