From 19e27ca78233b752759b7b8365e31982937db615 Mon Sep 17 00:00:00 2001
From: Warwick <warwick.l.e.new@gmail.com>
Date: Mon, 24 Nov 2025 09:58:04 +0000
Subject: [PATCH] Fixed tree deallocation by preventing the creation of copies
 on arena initialisation

---
 src/arena_allocator.c | 36 +++++++++++++++++++++++++++---------
 src/arena_allocator.h |  4 +++-
 src/main.c            | 19 +++++++++----------
 3 files changed, 39 insertions(+), 20 deletions(-)

diff --git a/src/arena_allocator.c b/src/arena_allocator.c
index 233d6e2..86057df 100644
--- a/src/arena_allocator.c
+++ b/src/arena_allocator.c
@@ -2,6 +2,7 @@
 #include <assert.h>
 #include <stddef.h>
 #include <stdlib.h>
+#include <string.h>
 
 #define DEFAUL_REGION_SIZE 1048576 /* 8 * 1024 * 1024 = 8MB */
 
@@ -12,33 +13,44 @@ Region *new_region(size_t capacity) {
   Region *region = malloc(capacity + sizeof(Region));
   assert(region != NULL);
   *region = (Region){.next = NULL, .capacity = capacity, .cursor = 0};
+
+  // Zero initialise memory
+  memset(region->data, 0, capacity);
+
   return region;
 }
 
-Arena arena_init(Arena *parent, size_t capacity) {
+Arena *arena_init(Arena *parent, size_t capacity) {
   Region *region = new_region(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){.begin = region, .end = region, .child = NULL, .sibling = NULL};
+    *current_arena = (Arena){.is_root = false,
+                             .begin = region,
+                             .end = region,
+                             .child = NULL,
+                             .sibling = NULL};
 
     // if parent has no children this arena is now it's child
     if (parent->child == NULL) {
       parent->child = current_arena;
-      return *current_arena;
+      return current_arena;
     }
 
     // Push the arena onto the first childs sibling list
     current_arena->sibling = parent->child;
     parent->child = current_arena;
-    return *current_arena;
+    return current_arena;
   }
 
-  // This is the root of the arena tree
-  Arena arena = {
-      .begin = region, .end = region, .child = NULL, .sibling = NULL};
+  // Create root of arena tree
+  Arena *arena = malloc(sizeof(Arena));
+  *arena = (Arena){.is_root = true,
+                   .begin = region,
+                   .end = region,
+                   .child = NULL,
+                   .sibling = NULL};
   return arena;
 }
 
@@ -62,7 +74,11 @@ void arena_deinit(Arena *arena) {
     region = next_region;
   }
 
-  *arena = (Arena){.begin = NULL, .end = NULL};
+  arena->begin = NULL;
+  arena->end = NULL;
+  if (arena->is_root) {
+    free(arena);
+  }
 }
 
 void *arena_alloc(Arena *arena, size_t size) {
@@ -79,6 +95,8 @@ void *arena_alloc(Arena *arena, size_t size) {
 
   void *result = &region->data[region->cursor];
   region->cursor += size;
+  // TODO: only align when needed
+  size = (size + 7) & ~7; // align size increase to multiple of 8
   return result;
 }
 
diff --git a/src/arena_allocator.h b/src/arena_allocator.h
index 423eedf..6dbe772 100644
--- a/src/arena_allocator.h
+++ b/src/arena_allocator.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <stdbool.h>
 #include <stddef.h>
 
 typedef struct Region_s Region;
@@ -12,13 +13,14 @@ struct Region_s {
 
 typedef struct Arena_s Arena;
 struct Arena_s {
+  bool is_root;
   Arena *child;
   Arena *sibling;
   Region *begin;
   Region *end;
 };
 
-Arena arena_init(Arena *parent, size_t capacity);
+Arena *arena_init(Arena *parent, size_t capacity);
 void arena_deinit(Arena *arena);
 
 void *arena_alloc(Arena *arena, size_t size);
diff --git a/src/main.c b/src/main.c
index 9eeb1ca..a0404d2 100644
--- a/src/main.c
+++ b/src/main.c
@@ -14,23 +14,22 @@
 int main(int argc, char *argv[]) {
   // arena allocation test
   printf("Allocation test\n");
-  Arena global_arena = arena_init(NULL, 0);
-  for (int i = 0; i <= 1048576+100; i++) {
-    int *number = arena_alloc(&global_arena, sizeof(int));
+  Arena *global_arena = arena_init(NULL, 0);
+  for (int i = 0; i <= 1048576 + 100; i++) {
+    int *number = arena_alloc(global_arena, sizeof(int));
     *number = 42;
   }
 
-  printf("children test\n");
-
   // arena children test
-  Arena child_arena = arena_init(&global_arena, 0);
-  //Arena sibling_arena = arena_init(&global_arena, 0);
-  //Arena grandchild_arena = arena_init(&child_arena, 0);
+  printf("children test\n");
+  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_deinit(&global_arena);
+  printf("deinit test\n");
+  arena_deinit(global_arena);
 
   printf("tests complete\n");
-  
 }
 
 /*int main(int argc, char *argv[]) {