objspace.c

/**********************************************************************

  objspace.c - ObjectSpace extender for MRI.

  $Author$
  created at: Wed Jun 17 07:39:17 2009

  NOTE: This extension library is only expected to exist with C Ruby.

  All the files in this distribution are covered under the Ruby's
  license (see the file COPYING).

**********************************************************************/

#include "internal.h"
#include <ruby/st.h>
#include <ruby/io.h>
#include <ruby/re.h>
#include "node.h"
#include "gc.h"

/*
 *  call-seq:
 *    ObjectSpace.memsize_of(obj) -> Integer
 *
 *  Return consuming memory size of obj.
 *
 *  Note that the return size is incomplete.  You need to deal with this
 *  information as only a *HINT*. Especially, the size of +T_DATA+ may not be
 *  correct.
 *
 *  This method is only expected to work with C Ruby.
 *
 *  From Ruby 2.2, memsize_of(obj) returns a memory size includes
  * sizeof(RVALUE).
 */

static VALUE
memsize_of_m(VALUE self, VALUE obj)
{
    return SIZET2NUM(rb_obj_memsize_of(obj));
}

struct total_data {
    size_t total;
    VALUE klass;
};

static int
total_i(void *vstart, void *vend, size_t stride, void *ptr)
{
    VALUE v;
    struct total_data *data = (struct total_data *)ptr;

    for (v = (VALUE)vstart; v != (VALUE)vend; v += stride) {
	if (RBASIC(v)->flags) {
	    switch (BUILTIN_TYPE(v)) {
	      case T_NONE:
	      case T_IMEMO:
	      case T_ICLASS:
	      case T_NODE:
	      case T_ZOMBIE:
		continue;
	      case T_CLASS:
		if (FL_TEST(v, FL_SINGLETON))
		  continue;
	      default:
		if (data->klass == 0 || rb_obj_is_kind_of(v, data->klass)) {
		    data->total += rb_obj_memsize_of(v);
		}
	    }
	}
    }

    return 0;
}

/*
 *  call-seq:
 *    ObjectSpace.memsize_of_all([klass]) -> Integer
 *
 *  Return consuming memory size of all living objects.
 *
 *  If +klass+ (should be Class object) is given, return the total memory size
 *  of instances of the given class.
 *
 *  Note that the returned size is incomplete. You need to deal with this
 *  information as only a *HINT*. Especially, the size of +T_DATA+ may not be
 *  correct.
 *
 *  Note that this method does *NOT* return total malloc'ed memory size.
 *
 *  This method can be defined by the following Ruby code:
 *
 *	def memsize_of_all klass = false
 *  	  total = 0
 *  	  ObjectSpace.each_object{|e|
 *  	    total += ObjectSpace.memsize_of(e) if klass == false || e.kind_of?(klass)
 *  	  }
 *  	  total
 *  	end
 *
 *  This method is only expected to work with C Ruby.
 */

static VALUE
memsize_of_all_m(int argc, VALUE *argv, VALUE self)
{
    struct total_data data = {0, 0};

    if (argc > 0) {
	rb_scan_args(argc, argv, "01", &data.klass);
    }

    rb_objspace_each_objects(total_i, &data);
    return SIZET2NUM(data.total);
}

static int
set_zero_i(st_data_t key, st_data_t val, st_data_t arg)
{
    VALUE k = (VALUE)key;
    VALUE hash = (VALUE)arg;
    rb_hash_aset(hash, k, INT2FIX(0));
    return ST_CONTINUE;
}

static int
cos_i(void *vstart, void *vend, size_t stride, void *data)
{
    size_t *counts = (size_t *)data;
    VALUE v = (VALUE)vstart;

    for (;v != (VALUE)vend; v += stride) {
	if (RBASIC(v)->flags) {
	    counts[BUILTIN_TYPE(v)] += rb_obj_memsize_of(v);
	}
    }
    return 0;
}

static VALUE
type2sym(enum ruby_value_type i)
{
    VALUE type;
    switch (i) {
#define CASE_TYPE(t) case t: type = ID2SYM(rb_intern(#t)); break;
	CASE_TYPE(T_NONE);
	CASE_TYPE(T_OBJECT);
	CASE_TYPE(T_CLASS);
	CASE_TYPE(T_MODULE);
	CASE_TYPE(T_FLOAT);
	CASE_TYPE(T_STRING);
	CASE_TYPE(T_REGEXP);
	CASE_TYPE(T_ARRAY);
	CASE_TYPE(T_HASH);
	CASE_TYPE(T_STRUCT);
	CASE_TYPE(T_BIGNUM);
	CASE_TYPE(T_FILE);
	CASE_TYPE(T_DATA);
	CASE_TYPE(T_MATCH);
	CASE_TYPE(T_COMPLEX);
	CASE_TYPE(T_RATIONAL);
	CASE_TYPE(T_NIL);
	CASE_TYPE(T_TRUE);
	CASE_TYPE(T_FALSE);
	CASE_TYPE(T_SYMBOL);
	CASE_TYPE(T_FIXNUM);
	CASE_TYPE(T_UNDEF);
	CASE_TYPE(T_IMEMO);
	CASE_TYPE(T_NODE);
	CASE_TYPE(T_ICLASS);
	CASE_TYPE(T_ZOMBIE);
#undef CASE_TYPE
      default: rb_bug("type2sym: unknown type (%d)", i);
    }
    return type;
}

/*
 *  call-seq:
 *    ObjectSpace.count_objects_size([result_hash]) -> hash
 *
 *  Counts objects size (in bytes) for each type.
 *
 *  Note that this information is incomplete.  You need to deal with
 *  this information as only a *HINT*.  Especially, total size of
 *  T_DATA may not right size.
 *
 *  It returns a hash as:
 *    {:TOTAL=>1461154, :T_CLASS=>158280, :T_MODULE=>20672, :T_STRING=>527249, ...}
 *
 *  If the optional argument, result_hash, is given,
 *  it is overwritten and returned.
 *  This is intended to avoid probe effect.
 *
 *  The contents of the returned hash is implementation defined.
 *  It may be changed in future.
 *
 *  This method is only expected to work with C Ruby.
 */

static VALUE
count_objects_size(int argc, VALUE *argv, VALUE os)
{
    size_t counts[T_MASK+1];
    size_t total = 0;
    enum ruby_value_type i;
    VALUE hash;

    if (rb_scan_args(argc, argv, "01", &hash) == 1) {
        if (!RB_TYPE_P(hash, T_HASH))
            rb_raise(rb_eTypeError, "non-hash given");
    }

    for (i = 0; i <= T_MASK; i++) {
	counts[i] = 0;
    }

    rb_objspace_each_objects(cos_i, &counts[0]);

    if (hash == Qnil) {
        hash = rb_hash_new();
    }
    else if (!RHASH_EMPTY_P(hash)) {
        st_foreach(RHASH_TBL(hash), set_zero_i, hash);
    }

    for (i = 0; i <= T_MASK; i++) {
	if (counts[i]) {
	    VALUE type = type2sym(i);
	    total += counts[i];
	    rb_hash_aset(hash, type, SIZET2NUM(counts[i]));
	}
    }
    rb_hash_aset(hash, ID2SYM(rb_intern("TOTAL")), SIZET2NUM(total));
    return hash;
}

static int
cn_i(void *vstart, void *vend, size_t stride, void *n)
{
    size_t *nodes = (size_t *)n;
    VALUE v = (VALUE)vstart;

    for (; v != (VALUE)vend; v += stride) {
	if (RBASIC(v)->flags && BUILTIN_TYPE(v) == T_NODE) {
	    size_t s = nd_type((NODE *)v);
	    nodes[s]++;
	}
    }

    return 0;
}

/*
 *  call-seq:
 *     ObjectSpace.count_nodes([result_hash]) -> hash
 *
 *  Counts nodes for each node type.
 *
 *  This method is only for MRI developers interested in performance and memory
 *  usage of Ruby programs.
 *
 *  It returns a hash as:
 *
 *	{:NODE_METHOD=>2027, :NODE_FBODY=>1927, :NODE_CFUNC=>1798, ...}
 *
 *  If the optional argument, result_hash, is given, it is overwritten and
 *  returned. This is intended to avoid probe effect.
 *
 *  Note:
 *  The contents of the returned hash is implementation defined.
 *  It may be changed in future.
 *
 *  This method is only expected to work with C Ruby.
 */

static VALUE
count_nodes(int argc, VALUE *argv, VALUE os)
{
    size_t nodes[NODE_LAST+1];
    size_t i;
    VALUE hash;

    if (rb_scan_args(argc, argv, "01", &hash) == 1) {
        if (!RB_TYPE_P(hash, T_HASH))
            rb_raise(rb_eTypeError, "non-hash given");
    }

    for (i = 0; i <= NODE_LAST; i++) {
	nodes[i] = 0;
    }

    rb_objspace_each_objects(cn_i, &nodes[0]);

    if (hash == Qnil) {
        hash = rb_hash_new();
    }
    else if (!RHASH_EMPTY_P(hash)) {
        st_foreach(RHASH_TBL(hash), set_zero_i, hash);
    }

    for (i=0; i<NODE_LAST; i++) {
	if (nodes[i] != 0) {
	    VALUE node;
	    switch (i) {
#define COUNT_NODE(n) case n: node = ID2SYM(rb_intern(#n)); break;
		COUNT_NODE(NODE_SCOPE);
		COUNT_NODE(NODE_BLOCK);
		COUNT_NODE(NODE_IF);
		COUNT_NODE(NODE_CASE);
		COUNT_NODE(NODE_WHEN);
		COUNT_NODE(NODE_OPT_N);
		COUNT_NODE(NODE_WHILE);
		COUNT_NODE(NODE_UNTIL);
		COUNT_NODE(NODE_ITER);
		COUNT_NODE(NODE_FOR);
		COUNT_NODE(NODE_BREAK);
		COUNT_NODE(NODE_NEXT);
		COUNT_NODE(NODE_REDO);
		COUNT_NODE(NODE_RETRY);
		COUNT_NODE(NODE_BEGIN);
		COUNT_NODE(NODE_RESCUE);
		COUNT_NODE(NODE_RESBODY);
		COUNT_NODE(NODE_ENSURE);
		COUNT_NODE(NODE_AND);
		COUNT_NODE(NODE_OR);
		COUNT_NODE(NODE_MASGN);
		COUNT_NODE(NODE_LASGN);
		COUNT_NODE(NODE_DASGN);
		COUNT_NODE(NODE_DASGN_CURR);
		COUNT_NODE(NODE_GASGN);
		COUNT_NODE(NODE_IASGN);
		COUNT_NODE(NODE_IASGN2);
		COUNT_NODE(NODE_CDECL);
		COUNT_NODE(NODE_CVASGN);
		COUNT_NODE(NODE_CVDECL);
		COUNT_NODE(NODE_OP_ASGN1);
		COUNT_NODE(NODE_OP_ASGN2);
		COUNT_NODE(NODE_OP_ASGN_AND);
		COUNT_NODE(NODE_OP_ASGN_OR);
		COUNT_NODE(NODE_OP_CDECL);
		COUNT_NODE(NODE_CALL);
		COUNT_NODE(NODE_FCALL);
		COUNT_NODE(NODE_VCALL);
		COUNT_NODE(NODE_SUPER);
		COUNT_NODE(NODE_ZSUPER);
		COUNT_NODE(NODE_ARRAY);
		COUNT_NODE(NODE_ZARRAY);
		COUNT_NODE(NODE_VALUES);
		COUNT_NODE(NODE_HASH);
		COUNT_NODE(NODE_RETURN);
		COUNT_NODE(NODE_YIELD);
		COUNT_NODE(NODE_LVAR);
		COUNT_NODE(NODE_DVAR);
		COUNT_NODE(NODE_GVAR);
		COUNT_NODE(NODE_IVAR);
		COUNT_NODE(NODE_CONST);
		COUNT_NODE(NODE_CVAR);
		COUNT_NODE(NODE_NTH_REF);
		COUNT_NODE(NODE_BACK_REF);
		COUNT_NODE(NODE_MATCH);
		COUNT_NODE(NODE_MATCH2);
		COUNT_NODE(NODE_MATCH3);
		COUNT_NODE(NODE_LIT);
		COUNT_NODE(NODE_STR);
		COUNT_NODE(NODE_DSTR);
		COUNT_NODE(NODE_XSTR);
		COUNT_NODE(NODE_DXSTR);
		COUNT_NODE(NODE_EVSTR);
		COUNT_NODE(NODE_DREGX);
		COUNT_NODE(NODE_DREGX_ONCE);
		COUNT_NODE(NODE_ARGS);
		COUNT_NODE(NODE_ARGS_AUX);
		COUNT_NODE(NODE_OPT_ARG);
		COUNT_NODE(NODE_KW_ARG);
		COUNT_NODE(NODE_POSTARG);
		COUNT_NODE(NODE_ARGSCAT);
		COUNT_NODE(NODE_ARGSPUSH);
		COUNT_NODE(NODE_SPLAT);
		COUNT_NODE(NODE_TO_ARY);
		COUNT_NODE(NODE_BLOCK_ARG);
		COUNT_NODE(NODE_BLOCK_PASS);
		COUNT_NODE(NODE_DEFN);
		COUNT_NODE(NODE_DEFS);
		COUNT_NODE(NODE_ALIAS);
		COUNT_NODE(NODE_VALIAS);
		COUNT_NODE(NODE_UNDEF);
		COUNT_NODE(NODE_CLASS);
		COUNT_NODE(NODE_MODULE);
		COUNT_NODE(NODE_SCLASS);
		COUNT_NODE(NODE_COLON2);
		COUNT_NODE(NODE_COLON3);
		COUNT_NODE(NODE_DOT2);
		COUNT_NODE(NODE_DOT3);
		COUNT_NODE(NODE_FLIP2);
		COUNT_NODE(NODE_FLIP3);
		COUNT_NODE(NODE_SELF);
		COUNT_NODE(NODE_NIL);
		COUNT_NODE(NODE_TRUE);
		COUNT_NODE(NODE_FALSE);
		COUNT_NODE(NODE_ERRINFO);
		COUNT_NODE(NODE_DEFINED);
		COUNT_NODE(NODE_POSTEXE);
		COUNT_NODE(NODE_ALLOCA);
		COUNT_NODE(NODE_BMETHOD);
		COUNT_NODE(NODE_DSYM);
		COUNT_NODE(NODE_ATTRASGN);
		COUNT_NODE(NODE_PRELUDE);
		COUNT_NODE(NODE_LAMBDA);
#undef COUNT_NODE
	      default: node = INT2FIX(i);
	    }
	    rb_hash_aset(hash, node, SIZET2NUM(nodes[i]));
	}
    }
    return hash;
}

static int
cto_i(void *vstart, void *vend, size_t stride, void *data)
{
    VALUE hash = (VALUE)data;
    VALUE v = (VALUE)vstart;

    for (; v != (VALUE)vend; v += stride) {
	if (RBASIC(v)->flags && BUILTIN_TYPE(v) == T_DATA) {
	    VALUE counter;
	    VALUE key = RBASIC(v)->klass;

	    if (key == 0) {
		const char *name = rb_objspace_data_type_name(v);
		if (name == 0) name = "unknown";
		key = ID2SYM(rb_intern(name));
	    }

	    counter = rb_hash_aref(hash, key);
	    if (NIL_P(counter)) {
		counter = INT2FIX(1);
	    }
	    else {
		counter = INT2FIX(FIX2INT(counter) + 1);
	    }

	    rb_hash_aset(hash, key, counter);
	}
    }

    return 0;
}

/*
 *  call-seq:
 *     ObjectSpace.count_tdata_objects([result_hash]) -> hash
 *
 *  Counts objects for each +T_DATA+ type.
 *
 *  This method is only for MRI developers interested in performance and memory
 *  usage of Ruby programs.
 *
 *  It returns a hash as:
 *
 *	{RubyVM::InstructionSequence=>504, :parser=>5, :barrier=>6,
 *  	 :mutex=>6, Proc=>60, RubyVM::Env=>57, Mutex=>1, Encoding=>99,
 *  	 ThreadGroup=>1, Binding=>1, Thread=>1, RubyVM=>1, :iseq=>1,
 *  	 Random=>1, ARGF.class=>1, Data=>1, :autoload=>3, Time=>2}
 *  	# T_DATA objects existing at startup on r32276.
 *
 *  If the optional argument, result_hash, is given, it is overwritten and
 *  returned. This is intended to avoid probe effect.
 *
 *  The contents of the returned hash is implementation specific and may change
 *  in the future.
 *
 *  In this version, keys are Class object or Symbol object.
 *
 *  If object is kind of normal (accessible) object, the key is Class object.
 *  If object is not a kind of normal (internal) object, the key is symbol
 *  name, registered by rb_data_type_struct.
 *
 *  This method is only expected to work with C Ruby.
 */

static VALUE
count_tdata_objects(int argc, VALUE *argv, VALUE self)
{
    VALUE hash;

    if (rb_scan_args(argc, argv, "01", &hash) == 1) {
        if (!RB_TYPE_P(hash, T_HASH))
            rb_raise(rb_eTypeError, "non-hash given");
    }

    if (hash == Qnil) {
        hash = rb_hash_new();
    }
    else if (!RHASH_EMPTY_P(hash)) {
        st_foreach(RHASH_TBL(hash), set_zero_i, hash);
    }

    rb_objspace_each_objects(cto_i, (void *)hash);

    return hash;
}

static void
iow_mark(void *ptr)
{
    rb_gc_mark((VALUE)ptr);
}

static size_t
iow_size(const void *ptr)
{
    VALUE obj = (VALUE)ptr;
    return rb_obj_memsize_of(obj);
}

static const rb_data_type_t iow_data_type = {
    "ObjectSpace::InternalObjectWrapper",
    {iow_mark, 0, iow_size,},
    0, 0, RUBY_TYPED_FREE_IMMEDIATELY
};

static VALUE rb_mInternalObjectWrapper;

static VALUE
iow_newobj(VALUE obj)
{
    return rb_data_typed_object_alloc(rb_mInternalObjectWrapper, (void *)obj, &iow_data_type);
}

/* Returns the type of the internal object. */
static VALUE
iow_type(VALUE self)
{
    VALUE obj = (VALUE)DATA_PTR(self);
    return type2sym(BUILTIN_TYPE(obj));
}

/* See Object#inspect. */
static VALUE
iow_inspect(VALUE self)
{
    VALUE obj = (VALUE)DATA_PTR(self);
    VALUE type = type2sym(BUILTIN_TYPE(obj));

    return rb_sprintf("#<InternalObject:%p %"PRIsVALUE">", (void *)obj, rb_sym2str(type));
}

/* Returns the Object#object_id of the internal object. */
static VALUE
iow_internal_object_id(VALUE self)
{
    VALUE obj = (VALUE)DATA_PTR(self);
    return rb_obj_id(obj);
}

struct rof_data {
    st_table *refs;
    VALUE internals;
};

static void
reachable_object_from_i(VALUE obj, void *data_ptr)
{
    struct rof_data *data = (struct rof_data *)data_ptr;
    VALUE key = obj;
    VALUE val = obj;

    if (rb_objspace_markable_object_p(obj)) {
	if (rb_objspace_internal_object_p(obj)) {
	    val = iow_newobj(obj);
	    rb_ary_push(data->internals, val);
	}
	st_insert(data->refs, key, val);
    }
}

static int
collect_values(st_data_t key, st_data_t value, st_data_t data)
{
    VALUE ary = (VALUE)data;
    rb_ary_push(ary, (VALUE)value);
    return ST_CONTINUE;
}

/*
 *  call-seq:
 *     ObjectSpace.reachable_objects_from(obj) -> array or nil
 *
 *  [MRI specific feature] Return all reachable objects from `obj'.
 *
 *  This method returns all reachable objects from `obj'.
 *
 *  If `obj' has two or more references to the same object `x', then returned
 *  array only includes one `x' object.
 *
 *  If `obj' is a non-markable (non-heap management) object such as true,
 *  false, nil, symbols and Fixnums (and Flonum) then it simply returns nil.
 *
 *  If `obj' has references to an internal object, then it returns instances of
 *  ObjectSpace::InternalObjectWrapper class. This object contains a reference
 *  to an internal object and you can check the type of internal object with
 *  `type' method.
 *
 *  If `obj' is instance of ObjectSpace::InternalObjectWrapper class, then this
 *  method returns all reachable object from an internal object, which is
 *  pointed by `obj'.
 *
 *  With this method, you can find memory leaks.
 *
 *  This method is only expected to work except with C Ruby.
 *
 *  Example:
 *    ObjectSpace.reachable_objects_from(['a', 'b', 'c'])
 *    #=> [Array, 'a', 'b', 'c']
 *
 *    ObjectSpace.reachable_objects_from(['a', 'a', 'a'])
 *    #=> [Array, 'a', 'a', 'a'] # all 'a' strings have different object id
 *
 *    ObjectSpace.reachable_objects_from([v = 'a', v, v])
 *    #=> [Array, 'a']
 *
 *    ObjectSpace.reachable_objects_from(1)
 *    #=> nil # 1 is not markable (heap managed) object
 *
 */

static VALUE
reachable_objects_from(VALUE self, VALUE obj)
{
    if (rb_objspace_markable_object_p(obj)) {
	VALUE ret = rb_ary_new();
	struct rof_data data;

	if (rb_typeddata_is_kind_of(obj, &iow_data_type)) {
	    obj = (VALUE)DATA_PTR(obj);
	}

	data.refs = st_init_numtable();
	data.internals = rb_ary_new();

	rb_objspace_reachable_objects_from(obj, reachable_object_from_i, &data);

	st_foreach(data.refs, collect_values, (st_data_t)ret);
	return ret;
    }
    else {
	return Qnil;
    }
}

struct rofr_data {
    VALUE categories;
    const char *last_category;
    VALUE last_category_str;
    VALUE last_category_objects;
};

static void
reachable_object_from_root_i(const char *category, VALUE obj, void *ptr)
{
    struct rofr_data *data = (struct rofr_data *)ptr;
    VALUE category_str;
    VALUE category_objects;

    if (category == data->last_category) {
	category_str = data->last_category_str;
	category_objects = data->last_category_objects;
    }
    else {
	data->last_category = category;
	category_str = data->last_category_str = rb_str_new2(category);
	category_objects = data->last_category_objects = rb_hash_new();
	rb_funcall(category_objects, rb_intern("compare_by_identity"), 0);
	if (!NIL_P(rb_hash_lookup(data->categories, category_str))) {
	    rb_bug("reachable_object_from_root_i: category should insert at once");
	}
	rb_hash_aset(data->categories, category_str, category_objects);
    }

    if (rb_objspace_markable_object_p(obj) &&
	obj != data->categories &&
	obj != data->last_category_objects) {
	if (rb_objspace_internal_object_p(obj)) {
	    obj = iow_newobj(obj);
	}
	rb_hash_aset(category_objects, obj, obj);
    }
}

static int
collect_values_of_values(VALUE category, VALUE category_objects, VALUE categories)
{
    VALUE ary = rb_ary_new();
    st_foreach(rb_hash_tbl(category_objects), collect_values, ary);
    rb_hash_aset(categories, category, ary);
    return ST_CONTINUE;
}

/*
 *  call-seq:
 *     ObjectSpace.reachable_objects_from_root -> hash
 *
 *  [MRI specific feature] Return all reachable objects from root.
 */
static VALUE
reachable_objects_from_root(VALUE self)
{
    struct rofr_data data;
    VALUE hash = data.categories = rb_hash_new();
    data.last_category = 0;

    rb_funcall(hash, rb_intern("compare_by_identity"), 0);
    rb_objspace_reachable_objects_from_root(reachable_object_from_root_i, &data);
    rb_hash_foreach(hash, collect_values_of_values, hash);

    return hash;
}

void Init_object_tracing(VALUE rb_mObjSpace);
void Init_objspace_dump(VALUE rb_mObjSpace);

/*
 * Document-module: ObjectSpace
 *
 * The objspace library extends the ObjectSpace module and adds several
 * methods to get internal statistic information about
 * object/memory management.
 *
 * You need to <code>require 'objspace'</code> to use this extension module.
 *
 * Generally, you *SHOULD NOT* use this library if you do not know
 * about the MRI implementation.  Mainly, this library is for (memory)
 * profiler developers and MRI developers who need to know about MRI
 * memory usage.
 */

void
Init_objspace(void)
{
    VALUE rb_mObjSpace;
#if 0
    rb_mObjSpace = rb_define_module("ObjectSpace"); /* let rdoc know */
#endif
    rb_mObjSpace = rb_const_get(rb_cObject, rb_intern("ObjectSpace"));

    rb_define_module_function(rb_mObjSpace, "memsize_of", memsize_of_m, 1);
    rb_define_module_function(rb_mObjSpace, "memsize_of_all", memsize_of_all_m, -1);

    rb_define_module_function(rb_mObjSpace, "count_objects_size", count_objects_size, -1);
    rb_define_module_function(rb_mObjSpace, "count_nodes", count_nodes, -1);
    rb_define_module_function(rb_mObjSpace, "count_tdata_objects", count_tdata_objects, -1);

    rb_define_module_function(rb_mObjSpace, "reachable_objects_from", reachable_objects_from, 1);
    rb_define_module_function(rb_mObjSpace, "reachable_objects_from_root", reachable_objects_from_root, 0);

    /*
     * This class is used as a return value from
     * ObjectSpace::reachable_objects_from.
     *
     * When ObjectSpace::reachable_objects_from returns an object with
     * references to an internal object, an instance of this class is returned.
     *
     * You can use the #type method to check the type of the internal object.
     */
    rb_mInternalObjectWrapper = rb_define_class_under(rb_mObjSpace, "InternalObjectWrapper", rb_cObject);
    rb_define_method(rb_mInternalObjectWrapper, "type", iow_type, 0);
    rb_define_method(rb_mInternalObjectWrapper, "inspect", iow_inspect, 0);
    rb_define_method(rb_mInternalObjectWrapper, "internal_object_id", iow_internal_object_id, 0);

    Init_object_tracing(rb_mObjSpace);
    Init_objspace_dump(rb_mObjSpace);
}