The ObjectSpace module contains a number of routines that interact with the garbage collection facility and allow you to traverse all living objects with an iterator.

ObjectSpace also provides support for object finalizers, procs that will be called when a specific object is about to be destroyed by garbage collection.

include ObjectSpace

a = "A"
b = "B"
c = "C"

define_finalizer(a, proc {|id| puts "Finalizer one on #{id}" })
define_finalizer(a, proc {|id| puts "Finalizer two on #{id}" })
define_finalizer(b, proc {|id| puts "Finalizer three on #{id}" })

produces:

Finalizer three on 537763470
Finalizer one on 537763480
Finalizer two on 537763480
Namespace
Methods
#
C
D
E
G
U
Class Public methods
ObjectSpace._id2ref(object_id) → an_object

Converts an object id to a reference to the object. May not be called on an object id passed as a parameter to a finalizer.

s = "I am a string"                    #=> "I am a string"
r = ObjectSpace._id2ref(s.object_id)   #=> "I am a string"
r == s                                 #=> true
static VALUE
id2ref(VALUE obj, VALUE objid)
{
#if SIZEOF_LONG == SIZEOF_VOIDP
#define NUM2PTR(x) NUM2ULONG(x)
#elif SIZEOF_LONG_LONG == SIZEOF_VOIDP
#define NUM2PTR(x) NUM2ULL(x)
#endif
    rb_objspace_t *objspace = &rb_objspace;
    VALUE ptr;
    void *p0;

    rb_secure(4);
    ptr = NUM2PTR(objid);
    p0 = (void *)ptr;

    if (ptr == Qtrue) return Qtrue;
    if (ptr == Qfalse) return Qfalse;
    if (ptr == Qnil) return Qnil;
    if (FIXNUM_P(ptr)) return (VALUE)ptr;
    if (FLONUM_P(ptr)) return (VALUE)ptr;
    ptr = obj_id_to_ref(objid);

    if ((ptr % sizeof(RVALUE)) == (4 << 2)) {
        ID symid = ptr / sizeof(RVALUE);
        if (rb_id2name(symid) == 0)
            rb_raise(rb_eRangeError, "%p is not symbol id value", p0);
        return ID2SYM(symid);
    }

    if (!is_id_value(objspace, ptr)) {
        rb_raise(rb_eRangeError, "%p is not id value", p0);
    }
    if (!is_live_object(objspace, ptr)) {
        rb_raise(rb_eRangeError, "%p is recycled object", p0);
    }
    return (VALUE)ptr;
}
ObjectSpace.count_objects([result_hash]) → hash

Counts objects for each type.

It returns a hash, such as:

{
  :TOTAL=>10000,
  :FREE=>3011,
  :T_OBJECT=>6,
  :T_CLASS=>404,
  # ...
}

The contents of the returned hash are implementation specific. It may be changed in future.

If the optional argument result_hash is given, it is overwritten and returned. This is intended to avoid probe effect.

This method is only expected to work on C Ruby.

static VALUE
count_objects(int argc, VALUE *argv, VALUE os)
{
    rb_objspace_t *objspace = &rb_objspace;
    size_t counts[T_MASK+1];
    size_t freed = 0;
    size_t total = 0;
    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 <= T_MASK; i++) {
        counts[i] = 0;
    }

    for (i = 0; i < heaps_used; i++) {
        RVALUE *p, *pend;

        p = objspace->heap.sorted[i]->start; pend = p + objspace->heap.sorted[i]->limit;
        for (;p < pend; p++) {
            if (p->as.basic.flags) {
                counts[BUILTIN_TYPE(p)]++;
            }
            else {
                freed++;
            }
        }
        total += objspace->heap.sorted[i]->limit;
    }

    if (hash == Qnil) {
        hash = rb_hash_new();
    }
    else if (!RHASH_EMPTY_P(hash)) {
        st_foreach(RHASH_TBL(hash), set_zero, hash);
    }
    rb_hash_aset(hash, ID2SYM(rb_intern("TOTAL")), SIZET2NUM(total));
    rb_hash_aset(hash, ID2SYM(rb_intern("FREE")), SIZET2NUM(freed));

    for (i = 0; i <= T_MASK; i++) {
        VALUE type;
        switch (i) {
#define COUNT_TYPE(t) case (t): type = ID2SYM(rb_intern(#t)); break;
            COUNT_TYPE(T_NONE);
            COUNT_TYPE(T_OBJECT);
            COUNT_TYPE(T_CLASS);
            COUNT_TYPE(T_MODULE);
            COUNT_TYPE(T_FLOAT);
            COUNT_TYPE(T_STRING);
            COUNT_TYPE(T_REGEXP);
            COUNT_TYPE(T_ARRAY);
            COUNT_TYPE(T_HASH);
            COUNT_TYPE(T_STRUCT);
            COUNT_TYPE(T_BIGNUM);
            COUNT_TYPE(T_FILE);
            COUNT_TYPE(T_DATA);
            COUNT_TYPE(T_MATCH);
            COUNT_TYPE(T_COMPLEX);
            COUNT_TYPE(T_RATIONAL);
            COUNT_TYPE(T_NIL);
            COUNT_TYPE(T_TRUE);
            COUNT_TYPE(T_FALSE);
            COUNT_TYPE(T_SYMBOL);
            COUNT_TYPE(T_FIXNUM);
            COUNT_TYPE(T_UNDEF);
            COUNT_TYPE(T_NODE);
            COUNT_TYPE(T_ICLASS);
            COUNT_TYPE(T_ZOMBIE);
#undef COUNT_TYPE
          default:              type = INT2NUM(i); break;
        }
        if (counts[i])
            rb_hash_aset(hash, type, SIZET2NUM(counts[i]));
    }

    return hash;
}
ObjectSpace.define_finalizer(obj, aProc=proc())

Adds aProc as a finalizer, to be called after obj was destroyed.

static VALUE
define_final(int argc, VALUE *argv, VALUE os)
{
    VALUE obj, block;

    rb_scan_args(argc, argv, "11", &obj, &block);
    rb_check_frozen(obj);
    if (argc == 1) {
        block = rb_block_proc();
    }
    else if (!rb_respond_to(block, rb_intern("call"))) {
        rb_raise(rb_eArgError, "wrong type argument %s (should be callable)",
                 rb_obj_classname(block));
    }

    return define_final0(obj, block);
}
ObjectSpace.each_object([module]) {|obj| ... } → fixnum
ObjectSpace.each_object([module]) → an_enumerator

Calls the block once for each living, nonimmediate object in this Ruby process. If module is specified, calls the block for only those classes or modules that match (or are a subclass of) module. Returns the number of objects found. Immediate objects (Fixnums, Symbols true, false, and nil) are never returned. In the example below, each_object returns both the numbers we defined and several constants defined in the Math module.

If no block is given, an enumerator is returned instead.

a = 102.7
b = 95       # Won't be returned
c = 12345678987654321
count = ObjectSpace.each_object(Numeric) {|x| p x }
puts "Total count: #{count}"

produces:

12345678987654321
102.7
2.71828182845905
3.14159265358979
2.22044604925031e-16
1.7976931348623157e+308
2.2250738585072e-308
Total count: 7
static VALUE
os_each_obj(int argc, VALUE *argv, VALUE os)
{
    VALUE of;

    rb_secure(4);
    if (argc == 0) {
        of = 0;
    }
    else {
        rb_scan_args(argc, argv, "01", &of);
    }
    RETURN_ENUMERATOR(os, 1, &of);
    return os_obj_of(of);
}
GC.start → nil
gc.garbage_collect → nil
ObjectSpace.garbage_collect → nil

Initiates garbage collection, unless manually disabled.

VALUE
rb_gc_start(void)
{
    rb_gc();
    return Qnil;
}
ObjectSpace.undefine_finalizer(obj)

Removes all finalizers for obj.

static VALUE
undefine_final(VALUE os, VALUE obj)
{
    return rb_undefine_final(obj);
}