From: "Dan0042 (Daniel DeLorme) via ruby-core" <ruby-core@...>
Date: 2023-11-15T14:06:40+00:00
Subject: [ruby-core:115398] [Ruby master Bug#8444] Regexp vars $~ and friends are not thread local

Issue #8444 has been updated by Dan0042 (Daniel DeLorme).


nobu (Nobuyoshi Nakada) wrote in #note-9:
> "Thread-local" in that sentence was wrong, and removed at commit:932dd9f10e684fa99b059054fbc934607d85b45a, but "method-local" is removed too.

Indeed, the documentation used to say "Regexp Global Variables" or "Special Global Variables" and this has been reduced to just "Global Variables" which I think is quite misleading. Sure they have the `$` sigil, but they're not global at all. If anything, "Special Variables" would be more accurate.

----------------------------------------
Bug #8444: Regexp vars $~ and friends are not thread local
https://bugs.ruby-lang.org/issues/8444#change-105335

* Author: jamespharaoh (James Pharaoh)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* ruby -v: trunk
----------------------------------------
In the docs for the Regexp special variables, `$~` and friends, it says "These global variables are thread-local and method-local variables". However the following gives an unexpected result:
  ```ruby
  def get_proc
    proc do |str|
      str =~ /(.+)/
      sleep 0.1
      puts "got #{$1} from #{str}\n"
    end
  end
  proc = get_proc
  t1 = Thread.new { proc.call "abc" }
  t2 = Thread.new { proc.call "def" }
  t1.join
  t2.join
  ```

This outputs the following:

  ```
  got abc from abc
  got abc from def
  ```

The expected result is of course:

  ```
  got abc from abc
  got def from def
  ```

Clearly the variables are being scoped to the `get_proc` method and are being shared by both threads. This runs contrary to the documentation and also to expectations.

This behaviour should either be changed, or the documentation updated to reflect the actual behaviour.

Interestingly, the following does work as expected:

  ```ruby
  proc = proc do |str|
    str =~ /(.+)/
    sleep 0.1
    puts "got #{$1} from #{str}\n"
  end
  t1 = Thread.new { proc.call "abc" }
  t2 = Thread.new { proc.call "def" }
  t1.join
  t2.join
  ```




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