[ruby-core:96811] [Ruby master Bug#16503] "ret: 2, hash modified during iteration" error in Ruby 2.7.0

[ko1@atdot.net]

Issue #16503 has been updated by ko1 (Koichi Sasada).


All right. I got a script:

```ruby
loop{
  h = {a:1, b:2, c:3, d:4, e:5, f:6, g:7, h:8}
  h.each{|k,v| GC.start; h.delete(k)}
}
```

The patch is:

```diff
diff --git a/hash.c b/hash.c
index 878f2b1790..644f85d6da 100644
--- a/hash.c
+++ b/hash.c
@@ -974,6 +974,7 @@ ar_foreach_check(VALUE hash, st_foreach_check_callback_func *func, st_data_t arg
 
             switch (retval) {
               case ST_CHECK: {
+                  pair = RHASH_AR_TABLE_REF(hash, i);
                   if (pair->key == never) break;
                   ret = ar_find_entry_hint(hash, hint, key);
                   if (ret == RHASH_AR_TABLE_MAX_BOUND) {
```

This patch should be back-ported for Ruby 2.6.

Thank you for your report.

----------------------------------------
Bug #16503: "ret: 2, hash modified during iteration" error in Ruby 2.7.0
https://bugs.ruby-lang.org/issues/16503#change-83806

* Author: jnchito (Junichi Ito)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-linux] (heroku-18 stack)
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
I am running a Rails app on Heroku. After upgrading to Ruby 2.7, I sometimes get `ret: 2, hash modified during iteration` error.

The same issue is reported here (I'm using meta-tags gem too):
https://github.com/kpumuk/meta-tags/issues/209

This gem deletes elements while iterating hash (HashWithIndifferentAccess actually), so I guess it might involve this error:
https://github.com/kpumuk/meta-tags/blob/v2.13.0/lib/meta_tags/renderer.rb#L168
https://github.com/kpumuk/meta-tags/blob/v2.13.0/lib/meta_tags/renderer.rb#L181
https://github.com/kpumuk/meta-tags/blob/v2.13.0/lib/meta_tags/meta_tags_collection.rb#L85

However, this error does not occur every time (sometimes works, sometimes fails), and it didn't occur in Ruby 2.6. So I'm wondering why. Do you have any idea on this?



-- 
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