Merge pull request #1 from thequux/master

First cut at allocator

.gitignore

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+*.o
+*~

config.mk

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+CFLAGS := $(shell pkg-config --cflags glib-2.0)
+LDFLAGS := $(shell pkg-config --libs glib-2.0)

lib/Makefile

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+include ../config.mk
+
+all: allocator.o
+
+%.o: %.c
+	gcc $(CFLAGS) -c -o $@ $^

lib/allocator.c

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+#include <glib.h>
+#include <stdint.h>
+#include <sys/types.h>
+
+#include "allocator.h"
+
+struct arena_link {
+  // TODO:
+  // For efficiency, we should probably allocate the arena links in 
+  // their own slice, and link to a block directly. That can be
+  // implemented later, though, with no change in interface.
+  struct arena_link *next; // It is crucial that this be the first item; so that 
+                           // any arena link can be casted to struct arena_link**.
+
+  size_t free;
+  size_t used;
+  uint8_t rest[];
+} ;
+
+struct arena {
+  struct arena_link *head;
+  size_t block_size;
+};
+
+arena_t new_arena(size_t block_size) {
+  struct arena *ret = g_new(struct arena, 1);
+  struct arena_link *link = (struct arena_link*)g_malloc0(sizeof(struct arena_link) + block_size);
+  link->free = block_size;
+  link->used = 0;
+  link->next = NULL;
+  ret->head = link;
+  ret->block_size = 0;
+
+  return ret;
+}
+
+void* arena_malloc(arena_t arena, size_t size) {
+  if (size <= arena->head->free) {
+    // fast path..
+    void* ret = arena->head->rest + arena->head->used;
+    arena->head->used += size;
+    arena->head->free -= size;
+    return ret;
+  } else if (size > arena->block_size) {
+    // We need a new, dedicated block for it, because it won't fit in a standard sized one.
+    // This involves some annoying casting...
+    void* link = g_malloc(size + sizeof(struct arena_link*));
+    *(struct arena_link**)link = arena->head->next;
+    arena->head->next = (struct arena_link*)link;
+    return (void*)((uint8_t*)link + sizeof(struct arena_link*));
+  } else {
+    // we just need to allocate an ordinary new block.
+    struct arena_link *link = (struct arena_link*)g_malloc0(sizeof(struct arena_link) + arena->block_size);
+    link->free = arena->block_size - size;
+    link->used = size;
+    link->next = arena->head;
+    arena->head = link;
+    return link->rest;
+  }
+}
+    
+void delete_arena(arena_t arena) {
+  struct arena_link *link = arena->head;
+  while (link) {
+    struct arena_link *next = link->next; 
+    // Even in the case of a special block, without the full arena
+    // header, this is correct, because the next pointer is the first
+    // in the structure.
+    g_free(link);
+    link = next;
+  }
+  g_free(arena);
+}

lib/allocator.h

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+#ifndef LIB_ALLOCATOR__H__
+#define LIB_ALLOCATOR__H__
+#include <sys/types.h>
+
+typedef struct arena* arena_t; // hidden implementation
+
+arena_t new_arena(size_t block_size); // pass 0 for default...
+void* arena_malloc(arena_t arena, size_t count); // TODO: needs the malloc attribute
+void delete_arena(arena_t arena);
+
+
+#endif // #ifndef LIB_ALLOCATOR__H__