WeakRef::RefError: Invalid Reference - probably recycled

[GregOnNet]

Hi,

first thanks for the great and consistent work on nanoc.
Me and my team really appreciate it.

Problem

I create the used items inside a preprocess rule.
After upgrading to Nanoc 4.2.0 I experience the following error when I access @item inside a template:

Message:

WeakRef::RefError: Invalid Reference - probably recycled

Compilation stack:

  (empty)

Environment

Nanoc 4.2.0 © 2007-2016 Denis Defreyne.
Running ruby 2.2.4 (2015-12-16) on x64-mingw32 with RubyGems 2.4.5.1.

crash.log
crash.txt

Let me know if I can provide further information to this topic

Kind Regards
Gregor

[agross]

Here's another stack trace with less haml and more nanoc:

crash.log.txt

[denisdefreyne]

Yup, I am getting this one as well. This is caused by the recent change of #846, though I am not quite sure why.

[denisdefreyne]

Potential fix in #865.

[agross]

The only reason for this to fail seems be that GC occurs between the check for weakref_alive? and the actual retrieval of the value.

[agross]

Probably it's best to disable GC during check and retrieval?

[agross]

Yes, it seems GC is the culprit.

I added this:

+       require 'pry-byebug'
+       prestat = GC.stat
        if method_cache.key?(args) && method_cache[args].weakref_alive?
+         begin
            method_cache[args].value
+          rescue => e
+            errstat = GC.stat
+            binding.pry
+            raise
+          end
        else
          send(original_method_name, *args).tap do |r|
            method_cache[args] = WeakRef.new(Wrapper.new(r))
          end
        end

When the debugger breaks I printed the GC count:

[3] pry(#<Nanoc::Int::OutdatednessChecker>)> prestat[:count]
50
[4] pry(#<Nanoc::Int::OutdatednessChecker>)> errstat[:count]
51

[denisdefreyne]

Correct. I have a fix in #865, which uses rescue WeakRef::RefError rather than checking #weakref_alive?.