From fef3dd609ab60a764a19863e0c9fe3bc7948be51 Mon Sep 17 00:00:00 2001
From: Krzosa Karol <krzosa.karol@gmail.com>
Date: Wed, 10 Jan 2024 07:35:01 +0100
Subject: [PATCH] Add "base_len" to memory arena so that bootstrap arena
 doesn't delete itself

---
 code/arena.c        | 13 ++++++-------
 code/arena.h        |  5 +++--
 test/test_arena.cpp | 21 +++++++++++++++++++++
 3 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/code/arena.c b/code/arena.c
index 5e366aa..ce88687 100644
--- a/code/arena.c
+++ b/code/arena.c
@@ -68,17 +68,14 @@ MA_StaticFunc uint8_t *MV__AdvanceCommit(MV_Memory *m, size_t *commit_size, size
     return result;
 }
 
-MA_API void MA_DeallocateStub(MA_Arena *arena, void *p) {}
-
 MA_API void MA_PopToPos(MA_Arena *arena, size_t pos) {
-    pos = MA_CLAMP_TOP(pos, arena->len);
+    MA_ASSERT(arena->len >= arena->base_len);
+    pos = MA_CLAMP(pos, arena->base_len, arena->len);
     arena->len = pos;
 }
 
-MA_API void *MA_PopSize(MA_Arena *arena, size_t size) {
-    size = MA_CLAMP_TOP(size, arena->len);
-    arena->len -= size;
-    return arena->memory.data + arena->len;
+MA_API void MA_PopSize(MA_Arena *arena, size_t size) {
+    MA_PopToPos(arena, arena->len - size);
 }
 
 MA_API void MA_DeallocateArena(MA_Arena *arena) {
@@ -153,6 +150,7 @@ MA_API MA_Arena *MA_Bootstrap(void) {
     MA_Arena bootstrap_arena = {0};
     MA_Arena *arena = MA_PushStruct(&bootstrap_arena, MA_Arena);
     *arena = bootstrap_arena;
+    arena->base_len = arena->len;
     return arena;
 }
 
@@ -160,6 +158,7 @@ MA_API M_Allocator MA_BootstrapExclusive(void) {
     MA_Arena bootstrap_arena = {0};
     MA_Arena *arena = MA_PushStruct(&bootstrap_arena, MA_Arena);
     *arena = bootstrap_arena;
+    arena->base_len = arena->len;
     return MA_GetExclusiveAllocator(arena);
 }
 
diff --git a/code/arena.h b/code/arena.h
index 28b1de4..94ec8ae 100644
--- a/code/arena.h
+++ b/code/arena.h
@@ -80,6 +80,8 @@ struct MA_Arena {
     MV_Memory memory;
     int alignment;
     size_t len;
+    size_t base_len; // When popping to 0 this is the minimum "len" value
+                     // It's so that Bootstrapped arena won't delete itself when Reseting.
 
 #ifdef __cplusplus
     operator M_Allocator() { return {this, MA_AllocatorProc}; }
@@ -130,9 +132,8 @@ MA_API MA_Checkpoint   MA_Save(MA_Arena *arena);
 MA_API void            MA_Load(MA_Checkpoint checkpoint);
 
 MA_API void            MA_PopToPos(MA_Arena *arena, size_t pos);
-MA_API void *          MA_PopSize(MA_Arena *arena, size_t size);
+MA_API void            MA_PopSize(MA_Arena *arena, size_t size);
 MA_API void            MA_DeallocateArena(MA_Arena *arena);
-MA_API void            MA_DeallocateStub(MA_Arena *arena, void *p);
 MA_API void            MA_Reset(MA_Arena *arena);
 
 MA_API void            MA_MemoryZero(void *p, size_t size);
diff --git a/test/test_arena.cpp b/test/test_arena.cpp
index b061d13..8f658f0 100644
--- a/test/test_arena.cpp
+++ b/test/test_arena.cpp
@@ -1,5 +1,25 @@
 #include "../core.c"
 
+void TestBootstrapArenaClear() {
+    MA_Arena *arena = MA_Bootstrap();
+    IO_Assert(arena->base_len != 0);
+
+    MA_PushSize(arena, 1024);
+    MA_Reset(arena);
+
+    int *vals = MA_PushArray(arena, int, 1024);
+    for (int i = 0; i < 1024; i += 1) {
+        vals[i] = i;
+    }
+
+    int *a = MA_PushStruct(arena, int);
+    *a = 1;
+
+    for (int i = 0; i < 1024; i += 1) {
+        IO_Assert(vals[i] == i);
+    }
+}
+
 void TestScratch() {
     MA_Arena *scratch_arena_test = NULL;
     {
@@ -76,4 +96,5 @@ int main() {
     TestCreateAllocate();
     TestBootstrap();
     TestBootstrapExclusive();
+    TestBootstrapArenaClear();
 }
\ No newline at end of file