Added: Arena allocator improvements

src/arena.c

@@ -1,40 +1,93 @@
+
 internal Arena *
-arena_initialize(u64 size)
+arena_initialize(u64 size, b8 growable)
 {
   Arena *result = 0;
-
-  void *backing_buffer = malloc(size);
+  void *backing_buffer = platform_memory_reserve(size);
 
   if (backing_buffer != NULL)
   {
-    result = (Arena*) backing_buffer;
+    platform_memory_commit(backing_buffer, ARENA_INITIAL_COMMIT_SIZE);
 
-    result->buffer = backing_buffer;
-    result->offset = sizeof(Arena); 
-    result->size   = sizeof(Arena) + size;
+    result = (Arena*) backing_buffer;
+    result->backing_buffer = (u64*) backing_buffer;
+    result->current = result;
+    result->prev = 0;
+
+    // rhjr: immutable arena header
+    result->base_pos =
+      memory_align(sizeof(Arena), ARENA_DEFAULT_ALIGNMENT);
+    result->offset = result->base_pos;
+
+    result->growable = growable;
+    result->size = size;
   }
 
+  // rhjr: arenas should be instantiated early on in the programs lifetime, that
+  //       is why this assertion will also be used in production.
+  ASSERT(result != 0);
+  return result;
+}
+
+internal Arena *
+arena_initialize_default()
+{
+  Arena *result = arena_initialize(ARENA_DEFAULT_RESERVE_SIZE, 1);
   return result;
 }
 
 internal void *
 arena_allocate(Arena *arena, u64 size)
 {
-  void *result = 0;
+  Arena *current = arena->current;
+  u64 pos_cur = current->base_pos + current->offset;
+  u64 pos_mem = memory_align(pos_cur, ARENA_DEFAULT_ALIGNMENT);
+  u64 pos_new = pos_mem + size;
 
-  if (arena->offset + size <= arena->size)
+  if (current->size < pos_new && current->growable)
   {
-    result = (void*)((u64) arena->buffer + (u64) arena->offset);
-    arena->offset += size;
+    Arena *new_memory_bock;
+
+    if (size > ARENA_DEFAULT_RESERVE_SIZE)
+    {
+      // rhjr: TODO add support for allocations larger then a single page, in a
+      //       single allocation call.
+      ASSERT(0);
+    }
+    else
+    {
+      new_memory_bock = arena_initialize_default();
+
+      if (new_memory_bock)
+      {
+        stack_push(arena->current, new_memory_bock, prev);
+
+        current = new_memory_bock;
+
+        pos_mem =
+          memory_align(current->offset, ARENA_DEFAULT_ALIGNMENT);
+        pos_new = current->offset + size;
+      }
+
+    }
 
-    memset(result, 0, size);
   }
 
-  return result;
+  void *memory = (void*)((u64) current->backing_buffer + pos_mem);
+  arena->offset = pos_new;
+
+  platform_memory_commit(memory, size);
+  memset(memory, 0, size);
+
+  return memory;
 }
 
 internal void
 arena_release(Arena *arena)
 {
-  arena->offset = 0;
+  for (Arena *node = arena->current, *prev = 0; node != 0; node = prev)
+  {
+    prev = node->prev;
+    platform_memory_release(node, node->size);
+  }
 }

src/arena.h

@@ -1,19 +1,30 @@
 #ifndef ARENA_H
 #define ARENA_H
 
+#define ARENA_INITIAL_COMMIT_SIZE sizeof(struct Arena)
+#define ARENA_DEFAULT_ALIGNMENT   0
+
+#ifndef ARENA_DEFAULT_RESERVE_SIZE
+#  define ARENA_DEFAULT_RESERVE_SIZE KB(4)
+#endif // ARENA_DEFAULT_RESERVE_SIZE
+
 typedef struct Arena Arena;
 struct Arena {
-  u64 *buffer;
+  struct Arena *current;
+  struct Arena *prev;
+  u64 *backing_buffer;
+  u64 base_pos;
   u64 offset;
   u64 size;
+  b8 growable;
 };
 
-internal Arena * arena_initialize(u64 size);
+//= rhjr: arenas
 
-internal void * arena_allocate(Arena *arena, u64 size);
-internal void   arena_release(Arena *arena);
+internal Arena * arena_initialize(u64 size, b8 growable);
+internal Arena * arena_initialize_default();
 
-//= rhjr: arena helpers
+internal void *  arena_allocate(Arena *arena, u64 size);
 
 #define arena_push_array(arena, type, count) \
   (type*) arena_allocate((arena), sizeof(type) * (count))
@@ -21,8 +32,12 @@ internal void   arena_release(Arena *arena);
 #define arena_push(arena, type) \
   (type*) arena_allocate((arena), sizeof(type))
 
+internal void arena_release(Arena *arena);
+
 //= rhjr: memory helpers
 
+#define memory_align(x, b) ((b != 0) ? (((x) + (b) - 1) & (~(b - 1))) : (x))
+
 #define memory_zero(s,z)       memset((s), 0, (z))
 #define memory_zero_struct(s)  memory_zero((s), sizeof(*(s)))