爲什麼`ObjectSpace._id2ref`在Ruby 1.9和Ruby 2.0上提供不同的輸出？

Question

爲什麼ObjectSpace._id2ref在Ruby 1.9和Ruby 2.0上有不同的輸出？

紅寶石1.9.3p392 I386-mingw32的

class Foo ; end 

Foo.object_id      #=> 17569464 
ObjectSpace._id2ref(17569464)  #=> Foo 

Foo.new.singleton_class.object_id #=> 17075124 
ObjectSpace._id2ref(17075124)  #=> "\x00" 

紅寶石2.0.0p0 I386-mingw32的

class Foo ; end 

Foo.object_id      #=> 17197176 
ObjectSpace._id2ref(17197176)  #=> Foo 

Foo.new.singleton_class.object_id #=> 19181436 
ObjectSpace._id2ref(19181436)  #=> RangeError: 0x124af7c is recycled object 

Foo.new.singleton_class.object_id #=> 17454324 
ObjectSpace._id2ref(17454324)  #=> RangeError: 0x10a54f4 is not id value 

Foo.new.singleton_class.object_id #=> 17139816 
ObjectSpace._id2ref(17139816)  #=> "c" 

Answer 1

只是因爲在2.0垃圾收集器是defter。對於

# RangeError: 0x124af7c is recycled object 

狀態的對象已經GC'ed。

UPD：我們可以Mutex接近要求的行爲：

2.0.0 (main):0 > Mutex.new.synchronize { 
2.0.0 (main):0 * class Foo ; end 
2.0.0 (main):0 * id = Foo.new.singleton_class.object_id 
2.0.0 (main):0 * puts id 
2.0.0 (main):0 * puts ObjectSpace._id2ref(id) 
2.0.0 (main):0 * } 
# 23172260 
# <Class:#<Foo:0x00000002c32970>>