From b5f3b197a4220460bbf793c8e4770f802c0d1c79 Mon Sep 17 00:00:00 2001
From: AmuroEita <1071307515@qq.com>
Date: Mon, 28 Sep 2026 01:41:48 +0800
Subject: [PATCH] Fix empty child capacity hint in box allocator

---
 CMakeLists.txt                       |  1 +
 include/slotsboxmalloc/doc.h         |  2 +-
 include/slotsboxmalloc/slotsboxobj.h |  2 +-
 tutorial/03_stress.c                 |  6 +++---
 tutorial/18_capacity_hint.c          | 23 +++++++++++++++++++++++
 tutorial/CMakeLists.txt              |  3 +++
 6 files changed, 32 insertions(+), 5 deletions(-)
 create mode 100644 tutorial/18_capacity_hint.c

diff --git a/CMakeLists.txt b/CMakeLists.txt
index cc092f4..1218aa3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,6 +6,7 @@ set(CMAKE_C_STANDARD_REQUIRED ON)
 set(CMAKE_C_EXTENSIONS OFF)
 
 include(GNUInstallDirs)
+include(CTest)
 
 # shared library (for FFI) + header-only (with SLOTSBOXMALLOC_IMPLEMENTATION)
 add_library(slotsboxmalloc SHARED
diff --git a/include/slotsboxmalloc/doc.h b/include/slotsboxmalloc/doc.h
index 165d7c8..68a8410 100644
--- a/include/slotsboxmalloc/doc.h
+++ b/include/slotsboxmalloc/doc.h
@@ -152,7 +152,7 @@
  *       box.children[i] = -1
  *       box.v2p[i] = box.p2v[i] = i     // 恒等映射 (预留)
  *
- *   box.child_max_cap = {level: objlevel+1, mult: 1}  // 满 box
+ *   box.child_max_cap = {level: 0, mult: 0}  // no children
  */
 
 /* --- 3.2 alloc_box_slot: 分配一个子 box slot（从左侧） ---
diff --git a/include/slotsboxmalloc/slotsboxobj.h b/include/slotsboxmalloc/slotsboxobj.h
index 113711c..9035c62 100644
--- a/include/slotsboxmalloc/slotsboxobj.h
+++ b/include/slotsboxmalloc/slotsboxobj.h
@@ -292,7 +292,7 @@ static inline void sbo_box_format(sbo_meta_t *meta, sbo_box_t *box,
         box->slots[i].state = SBO_FREE;
         box->children[i] = -1;
     }
-    box->child_max_cap = (sbo_usage_t){objlevel + 1, 1};
+    box->child_max_cap = (sbo_usage_t){0, 0};
 }
 
 /* ================================================================
diff --git a/tutorial/03_stress.c b/tutorial/03_stress.c
index d473099..1f0e554 100644
--- a/tutorial/03_stress.c
+++ b/tutorial/03_stress.c
@@ -10,14 +10,14 @@
 int main() {
     // 初始化 slotsboxmalloc 的元数据和数据区，使用更大的内存池以支持高负载
     uint8_t *buddy = malloc(4 * 1024 * 1024);     // 元数据区，增大到4MB
-    uint8_t *data = malloc(64 * 1024 * 1024);     // 数据区，增大到64MB
+    uint8_t *data = malloc(128 * 1024 * 1024);
     if (!buddy || !data) {
         perror("Failed to allocate memory for slotsboxmalloc");
         return 1;
     }
 
     // 初始化 slotsboxmalloc
-    if (sbo_init(buddy, 4 * 1024 * 1024, 64 * 1024 * 1024) != 0) {
+    if (sbo_init(buddy, 4 * 1024 * 1024, 128 * 1024 * 1024) != 0) {
         printf("Failed to initialize slotsboxmalloc\n");
         free(buddy);
         free(data);
@@ -104,4 +104,4 @@ int main() {
     free(data);
     printf("Stress test completed after %lld loops.\n", loop_count);
     return 0;
-}
\ No newline at end of file
+}
diff --git a/tutorial/18_capacity_hint.c b/tutorial/18_capacity_hint.c
new file mode 100644
index 0000000..14c4714
--- /dev/null
+++ b/tutorial/18_capacity_hint.c
@@ -0,0 +1,23 @@
+#define BLOCKMALLOC_IMPLEMENTATION
+#include <blockmalloc/blockmalloc.h>
+#define SLOTSBOXMALLOC_IMPLEMENTATION
+#include <slotsboxmalloc/slotsboxobj.h>
+
+int main(void) {
+    sbo_box_t box;
+    sbo_box_format(NULL, &box, 1, 0);
+    if (box.child_max_cap.level != 0 || box.child_max_cap.multiple != 0)
+        return 1;
+
+    for (int i = 0; i < SBO_N; i++) {
+        if (sbo_alloc_obj_slots(NULL, &box, 1) < 0)
+            return 2;
+    }
+    if (sbo_usage_cmp(sbo_box_and_child_max_cap(&box), (sbo_usage_t){0, 0}) != 0)
+        return 3;
+
+    sbo_free_obj_slots(NULL, &box, 0);
+    if (sbo_usage_cmp(sbo_box_and_child_max_cap(&box), (sbo_usage_t){1, 1}) != 0)
+        return 4;
+    return 0;
+}
diff --git a/tutorial/CMakeLists.txt b/tutorial/CMakeLists.txt
index 9551d40..1ba6121 100644
--- a/tutorial/CMakeLists.txt
+++ b/tutorial/CMakeLists.txt
@@ -71,3 +71,6 @@ target_link_libraries(16_bench_malloc slotsboxmalloc Threads::Threads)
 
 add_executable(17_data_integrity 17_data_integrity.c)
 target_link_libraries(17_data_integrity slotsboxmalloc)
+
+add_executable(18_capacity_hint 18_capacity_hint.c)
+add_test(NAME 18_capacity_hint COMMAND 18_capacity_hint)