makefile.c

#include <ruby.h>

struct my_malloc {
    size_t size;
    void *ptr;
};

static void
my_malloc_free(void *p) {
    struct my_malloc *ptr = p;
    
    if (ptr-&gt;size &gt; 0)
    free(ptr-&gt;ptr);
}

static VALUE
my_malloc_alloc(VALUE klass) {
    VALUE obj;
    struct my_malloc *ptr;
    
    obj = Data_Make_Struct(klass, struct my_malloc, NULL, my_malloc_free, ptr);
    
    ptr-&gt;size = 0;
    ptr-&gt;ptr  = NULL;
    
    return obj;
}

static VALUE
my_malloc_init(VALUE self, VALUE size) {
    struct my_malloc *ptr;
    size_t requested = NUM2SIZET(size);
    
    if (0 == requested)
    rb_raise(rb_eArgError, "unable to allocate 0 bytes");
    
    Data_Get_Struct(self, struct my_malloc, ptr);
    
    ptr-&gt;ptr = malloc(requested);
    
    if (NULL == ptr-&gt;ptr)
    rb_raise(rb_eNoMemError, "unable to allocate %ld bytes", requested);
    
    ptr-&gt;size = requested;
    
    return self;
}

static VALUE
my_malloc_release(VALUE self) {
    struct my_malloc *ptr;
    
    Data_Get_Struct(self, struct my_malloc, ptr);
    
    if (0 == ptr-&gt;size)
    return self;
    
    ptr-&gt;size = 0;
    free(ptr-&gt;ptr);
    
    return self;
}

void
Init_my_malloc(void) {
    VALUE cMyMalloc;
    
    cMyMalloc = rb_const_get(rb_cObject, rb_intern("MyMalloc"));
    
    rb_define_alloc_func(cMyMalloc, my_malloc_alloc);
    rb_define_method(cMyMalloc, "initialize", my_malloc_init, 1);
    rb_define_method(cMyMalloc, "free", my_malloc_release, 0);
}