1.0.3 - Renamed parameter bytes to size in arena_alloc()

.gitignore

@@ -0,0 +1 @@
+test

README.md

@@ -1,7 +1,8 @@
 # arena.h
 
 A single header library that implements
-[region-based memory management](https://en.wikipedia.org/wiki/Region-based_memory_management) in C.
+[region-based memory management](https://en.wikipedia.org/wiki/Region-based_memory_management)
+in C using a linked list approach.
 
 ## Example
 
@@ -11,12 +12,13 @@ A single header library that implements
 
 int main(void)
 {
-    Arena a = {0};
+    Arena a = {0}; // or arena_create(...) to specify a custom region
+                   // capacity just for this arena
 
-    int *x = arena_alloc(&a, sizeof(*x) * 69);
-    float *y = arena_alloc(&a, sizeof(*y) * 420);
+    int *x = arena_alloc(&a, sizeof(*x) * 32);
+    float *y = arena_alloc(&a, sizeof(*y) * 512);
 
-    arena_free(&a);
+    arena_free(&a); // The arena can still be reused
     return 0;
 }
 ```

arena.h

@@ -1,84 +1,232 @@
+// arena.h - v1.0.3 - MIT License - https://github.com/seajee/arena.h
+// single header library for region-based memory management.
+//
+// [License and changelog]
+//
+//     See end of file.
+//
+// [Single header library usage]
+//
+//     Including this header file as such does what you normally expect.
+//
+//     If you also need to include all of the function implementations you
+//     need to #define ARENA_IMPLEMENTATION before including the header file
+//     like this:
+//
+//         #define ARENA_IMPLEMENTATION
+//         #include "arena.h"
+//
+// [Compile-time options]
+//
+//     Note: every compile-time option listed here should be configured before
+//           the #include "arena.h"
+//
+//     #define ARENA_NO_ASSERT
+//
+//         This macro disables assertions that happen when a reallocation
+//         fails. The disabled assertions will be replaced with a simple
+//         condition that returns NULL when it fails. Note that ARENA_ASSERT
+//         is only used in arena_alloc().
+//
+//     #define ARENA_REGION_CAPACITY new_region_capacity_in_bytes (4096)
+//
+//         This macro defines the default capacity for arena regions.
+//
+//     #define ARENA_ASSERT my_assert
+//
+//         This macro defines an alternative function for assertions. In this
+//         library, ARENA_ASSERT is only used when arena_alloc() fails. Will
+//         be overwritten if ARENA_NO_ASSERT is defined.
+//
+//     #define ARENA_REALLOC my_realloc
+//     #define ARENA_FREE my_free
+//
+//         These macros define alternative functions for dynamic allocation
+//         and deallocation on the heap. They are only used for managing
+//         Arena_Region structures.
+//
+// [Function documentation]
+//
+// In this library, arenas are implemented as linked lists of regions. Each
+// region will contain the allocated buffers. The following are all of the
+// functions
+//
+//     Arena arena_create(size_t region_capacity)
+//
+// This function initializes an arena with a specified region capacity. By
+// default the region capacity is ARENA_REGION_CAPACITY, which can be
+// configured by redefining it before including the header file. This function
+// is not strictly necessary for initializing an arena (see example).
+//
+//     void *arena_alloc(Arena *a, size_t size)
+//
+// This function allocates a buffer of <size> bytes into the specified arena
+// and returns it's pointer.
+//
+//     void arena_free(Arena *a)
+//
+// This function frees all of the regions allocated in the specified arena
+// which invalidates all the pointers associated with the arena. The arena can
+// still be reused. If the arena was created with arena_create() the
+// configured region_capacity will be retained.
+//
+//     void arena_reset(Arena *a)
+//
+// This function resets an arena by keeping all of the regions allocated but
+// invalidates all of the pointers associated with the specified arena.
+// Warning: this functions may cause fragmentation, consider setting an
+// appropriate region capacity.
+//
+// [Example]
+//
+#if 0
+#define ARENA_IMPLEMENTATION
+#include "arena.h"
+
+int main(void)
+{
+    Arena a = {0}; // or arena_create(...) to specify a custom region
+                   // capacity just for this arena
+
+    int *x = arena_alloc(&a, sizeof(*x) * 32);
+    float *y = arena_alloc(&a, sizeof(*y) * 512);
+
+    arena_free(&a); // The arena can still be reused
+    return 0;
+}
+#endif // [Example]
+
 #ifndef ARENA_H_
 #define ARENA_H_
 
 #include <stddef.h>
 #include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
 
-#ifndef ARENA_MIN_CAPACITY
-#define ARENA_MIN_CAPACITY 4096
-#endif // ARENA_MIN_CAPACITY
+#ifndef ARENA_REGION_CAPACITY
+#    define ARENA_REGION_CAPACITY (8*1024)
+#endif // ARENA_REGION_CAPACITY
+
+#ifndef ARENA_NO_ASSERT
+#    ifndef ARENA_ASSERT
+#        include <assert.h>
+#        define ARENA_ASSERT assert
+#    endif // ARENA_ASSERT
+#else
+#    define ARENA_ASSERT(...) ((void)0)
+#endif // ARENA_NO_ASSERT
+
+#ifndef ARENA_REALLOC
+#    include <stdlib.h>
+#    define ARENA_REALLOC realloc
+#endif // ARENA_REALLOC
+
+#ifndef ARENA_FREE
+#    include <stdlib.h>
+#    define ARENA_FREE free
+#endif // ARENA_FREE
+
+#ifdef __cplusplus
+extern "C" { // Prevent name mangling of functions
+#endif // __cplusplus
 
 typedef struct Arena_Region Arena_Region;
 
 struct Arena_Region {
+    Arena_Region *next;
     size_t count;
     size_t capacity;
-    Arena_Region *next;
     uint8_t data[];
 };
 
-typedef struct {
+typedef struct Arena {
     Arena_Region *head;
     Arena_Region *tail;
+    size_t region_capacity;
 } Arena;
 
-void *arena_alloc(Arena *a, size_t bytes);
+Arena arena_create(size_t region_capacity);
+void *arena_alloc(Arena *a, size_t size);
 void arena_free(Arena *a);
 void arena_reset(Arena *a);
 
+#ifdef __cplusplus
+}
+#endif // __cplusplus
+
 #endif // ARENA_H_
 
 #ifdef ARENA_IMPLEMENTATION
 
-void *arena_alloc(Arena *a, size_t bytes)
+#ifdef __cplusplus
+extern "C" { // Prevent name mangling of functions
+#endif // __cplusplus
+
+Arena arena_create(size_t region_capacity)
 {
-    if (a == NULL) {
+    Arena a = {0};
+    a.region_capacity = region_capacity;
+    return a;
+}
+
+void *arena_alloc(Arena *a, size_t size)
+{
+    if (a == NULL || size == 0) {
+        ARENA_ASSERT(!"Invalid, parameters");
         return NULL;
     }
 
+    size_t region_capacity = (a->region_capacity == 0
+            ? ARENA_REGION_CAPACITY : a->region_capacity);
+
     // Empty arena
     if (a->head == NULL) {
-        size_t size = (bytes > ARENA_MIN_CAPACITY ? bytes : ARENA_MIN_CAPACITY);
-        a->head = (Arena_Region*)malloc(sizeof(*a->head) + size);
+        size_t alloc_size = (size > region_capacity ? size : region_capacity);
+        a->head = (Arena_Region*)ARENA_REALLOC(
+                NULL, sizeof(*a->head) + alloc_size);
+
         if (a->head == NULL) {
+            ARENA_ASSERT(!"Reallocation failed");
             return NULL;
         }
-        memset(a->head, 0, sizeof(*a->head));
-        a->head->count = bytes;
-        a->head->capacity = size;
+
+        a->head->next = NULL;
+        a->head->count = size;
+        a->head->capacity = alloc_size;
         a->tail = a->head;
         return a->head->data;
     }
 
     // Not enough capacity
-    if (bytes > a->tail->capacity - a->tail->count) {
+    if (size > a->tail->capacity - a->tail->count) {
         // Find first suitable region
-        while (a->tail->next != NULL && bytes > a->tail->capacity - a->tail->count) {
+        while (a->tail->next != NULL
+                && size > a->tail->capacity - a->tail->count) {
             a->tail = a->tail->next;
         }
 
-        // If found allocate on that region
-        if (bytes <= a->tail->capacity - a->tail->count) {
-            a->tail->count += bytes;
-            return a->tail->data + a->tail->count;
-        }
+        // If not found create a new region
+        if (size > a->tail->capacity - a->tail->count) {
+            size_t alloc_size =
+                (size > region_capacity ? size : region_capacity);
+
+            a->tail->next = (Arena_Region*)ARENA_REALLOC(
+                    NULL, sizeof(*a->tail) + alloc_size);
 
-        // If not create a new region
-        a->tail->next = (Arena_Region*)malloc(sizeof(*a->tail) + bytes);
             if (a->tail->next == NULL) {
+                ARENA_ASSERT(!"Reallocation failed");
                 return NULL;
             }
+
             a->tail = a->tail->next;
-        memset(a->tail, 0, sizeof(*a->tail));
-        a->tail->count = bytes;
-        a->tail->capacity = bytes;
+            a->tail->next = NULL;
+            a->tail->count = size;
+            a->tail->capacity = alloc_size;
             return a->tail->data;
         }
+    }
 
-    a->tail->count += bytes;
-    return a->tail->data + a->tail->count;
+    a->tail->count += size;
+    return a->tail->data + a->tail->count - size;
 }
 
 void arena_free(Arena *a)
@@ -90,11 +238,13 @@ void arena_free(Arena *a)
     Arena_Region *cur = a->head;
     while (cur != NULL) {
         Arena_Region *next = cur->next;
-        free(cur);
+        ARENA_FREE(cur);
         cur = next;
     }
 
-    memset(a, 0, sizeof(*a));
+    a->head = NULL;
+    a->tail = NULL;
+    // a->region_capacity = 0;
 }
 
 void arena_reset(Arena *a)
@@ -110,4 +260,42 @@ void arena_reset(Arena *a)
     a->tail = a->head;
 }
 
+#ifdef __cplusplus
+}
+#endif // __cplusplus
+
 #endif // ARENA_IMPLEMENTATION
+
+/*
+ * Revision history:
+ *
+ *     1.0.3 (2025-09-10) Renamed parameter bytes to size in arena_alloc()
+ *     1.0.2 (2025-09-06) Bug fixes; new ARENA_NO_ASSERT macro
+ *     1.0.1 (2025-08-02) Prevent name mangling of functions; don't reset
+ *                        region_capacity in arena_free()
+ *     1.0.0 (2025-07-24) Initial release
+ */
+
+/*
+ * MIT License
+ *
+ * Copyright (c) 2025 seajee
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */

test.c

@@ -2,13 +2,12 @@
 #include <stdlib.h>
 
 #ifdef DEBUG
-#define malloc(n) (printf("%s:%d:%s: malloc(%ld)\n",\
-            __FILE__, __LINE__, __func__, (n)), malloc((n)));
+#define realloc(p, s) (printf("%s:%d:%s: realloc(%p, %lu)\n",\
+            __FILE__, __LINE__, __func__, (p), (s)), realloc((p), (s)));
 #define free(p)   (printf("%s:%d:%s: free(%p)\n",\
             __FILE__, __LINE__, __func__, (p)), free((p)));
 #endif // DEBUG
 
-#define ARENA_MIN_CAPACITY 400
 #define ARENA_IMPLEMENTATION
 #include "arena.h"