Bug #21354: Symbol#to_proc is not ractor safe

• Status: Closed
• Assignee: ko1 (Koichi Sasada)
• Target version: -
• Backport: 3.2: REQUIRED, 3.3: REQUIRED, 3.4: REQUIRED

[luke-gru (Luke Gruber)]

There is caching in Symbol#to_proc (rb_sym_to_proc) that makes the assumption that we're always in the main ractor. With multiple ractors, this caching logic is not ractor-safe in that cached procs created in one ractor can leak into other ractors. In a debug build, this results in a ractor_confirm_belonging assertion failure.

Ruby code that reproduces the issue:

  :inspect.to_proc
  Ractor.new do
    :inspect.to_proc
  end.take

[luke-gru (Luke Gruber)]

PR here: https://github.com/ruby/ruby/pull/13380

We are looking at how to make the cache ractor safe but it will be done in a separate PR.

[nobu (Nobuyoshi Nakada)]

• Assignee set to ko1 (Koichi Sasada)
• Backport changed from 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN to 3.2: REQUIRED, 3.3: REQUIRED, 3.4: REQUIRED

• Status changed from Open to Closed

Applied in changeset git|f6cbf499bc98b851034fffb49fcbb59d495f6f7b.

---

Fix Symbol#to_proc (rb_sym_to_proc) to be ractor safe

In non-main ractors, don't use sym_proc_cache. It is not thread-safe
to add to this array without a lock and also it leaks procs from one
ractor to another. Instead, we create a new proc each time. If this
results in poor performance we can come up with a solution later.

Fixes [Bug #21354]