Retain and release!

gistfile1.txt

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>

struct SObject
{
  uint32_t retainCount;
  void *buffer;
};

typedef struct SObject Object;

Object *alloc(size_t length);
Object *retain(Object *object);
Object *release(Object *object);
void dealloc(Object *object);
void expect(uint8_t condition, const char *message);

/**
 * Allocate a retain-counted buffer n-bytes long.
 */
Object *alloc(size_t length)
{
  Object *object = malloc(sizeof(Object));
  object->retainCount = 0;
  object->buffer = malloc(length);
  return retain(object);
}

Object *retain(Object *object)
{
  object->retainCount++;
  return object;
}

Object *release(Object *object)
{
  object->retainCount = object->retainCount - 1;
  if (object->retainCount <= 0) {
    dealloc(object);
    return NULL;
  } else {
    return object;
  }
}

/**
 * Used by release to clean up the object
 */
void dealloc(Object *object)
{
  free(object->buffer);
  object->buffer = NULL;
  free(object);
}

/**
 * Yells when things break
 */
void expect(uint8_t condition, const char *message)
{
  if (!condition) {
    printf("assertion failed: %s\n", message);
  }
}

/**
 * Don't look at retain count. It's just a test. Don't look at it otherwise!
 */
int main(int argc, char **argv)
{
    Object *object = alloc(1024);
    expect(object->retainCount == 1, "object should have +1 retain");
    expect(object != NULL, "buffer should exist");

    retain(object);
    expect(object->retainCount == 2, "object should have +2 retain");

    release(object);
    expect(object->retainCount == 1, "object should have +1 retain");

    release(object);
}