Bug #18933: Dir.tmpdir implemented in non-Ractor-safe manner

• Status: Open
• Priority: Normal
• Assignee: -
• Target version: -
• ruby -v: ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-darwin21]
• Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN

[kreynolds (Kelley Reynolds)]

Background

Inside a Ractor, it is expected that generating a temporary directory using Dir.tmpdir will work. The current implementation uses a number of things which are not considered Rector-safe and will require refactoring.

How to reproduce

Ractor.new { Dir.tmpdir }

Expectation and result

The result is expected to be something along the lines of "/var/folders/xm/y4c00x0s26sgf_zlnqjh_7800000gn/T" but instead a Ractor::IsolationError exception is raised:

3.1.2/lib/ruby/3.1.0/tmpdir.rb:23:in `tmpdir': can not access class variables from non-main Ractors (Ractor::IsolationError)

Suggested solutions

• Make cached class variable a shareable constant
• Modify how random values are generated to be Rector-safe

[kreynolds (Kelley Reynolds)]

• File tmpdir.diff tmpdir.diff added

Attached is a possible solution for this

[nobu (Nobuyoshi Nakada)]

In Ruby 3.0, an instance variable also is not accessible from non-main Ractor.

[headius (Charles Nutter)]

Why not just put this in a private constant? I believe that would be Ractor-safe and it would make more sense than a lazy class variable or class instance variable (that's not actually lazy).