Bug #15262
Updated by nobu (Nobuyoshi Nakada) over 5 years ago
Given the following program: ```ruby require "weakref" Thread.abort_on_exception = true class Adder def self.start_adder(obj) obj.add end def initialize @qu = Queue.new @mutex = Mutex.new @mutex.lock begin @count = 10 @count.times do Thread.new(WeakRef.new(self), &self.class.method(:start_adder)) end ensure @mutex.unlock end @qu.deq end def add @mutex.lock begin @count-=1 if @count == 0 @qu.enq true elsif @count < 0 raise "shouldn't happen" end ensure @mutex.unlock end end end def test_adder 10.times.map do Thread.new do Adder.new end end.each(&:join) end 100.times do test_adder end ``` ## Expected behaviour: The program should simply execute without error. This is the case on JRuby but not on MRI. ## Actual behavior: The program stops with a probability of approximately 80% with the following error: ``` $ ruby -W2 adder-test.rb #<Thread:0x0000562d5089fea8@adder-test.rb:6 run> terminated with exception (report_on_exception is true): Traceback (most recent call last): adder-test.rb:7:in `start_adder': Invalid Reference - probably recycled (WeakRef::RefError) Traceback (most recent call last): adder-test.rb:7:in `start_adder': Invalid Reference - probably recycled (WeakRef::RefError) ``` Although `start_adder` start_adder works with a `WeakRef`, WeakRef, the `Adder` Adder object should still be GC marked, since `Adder.new` Adder.new doesn't return before all calls to `start_adder` start_adder finished. I verified this on ruby-trunk, but get mostly the same behavior on all older MRI versions.