From: headius@headius.com
To: ruby-core@ruby-lang.org
Subject: [ruby-core:103160] [Ruby master Bug#12689] Thread isolation of $~ and $_
Date: Thu, 01 Apr 2021 20:51:30 +0000 (UTC) [thread overview]
Message-ID: <redmine.journal-91232.20210401205129.286@ruby-lang.org> (raw)
In-Reply-To: redmine.issue-12689.20160819063718.286@ruby-lang.org
Issue #12689 has been updated by headius (Charles Nutter).
Also note this experimental PR that eliminates the update of `$~` from String#split, since no specs and no tests check that behavior and it seems unexpected and unpredictable (it updates to the last match during the split loop).
https://github.com/jruby/jruby/pull/6646
And a bug I just filed to eliminate backref updating from `start_with?` which should be a fast boolean check and not create a MatchData or update backref:
https://bugs.ruby-lang.org/issues/17771
----------------------------------------
Bug #12689: Thread isolation of $~ and $_
https://bugs.ruby-lang.org/issues/12689#change-91232
* Author: headius (Charles Nutter)
* Status: Open
* Priority: Normal
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
----------------------------------------
We are debating what is correct behavior now, and what should be correct behavior in the future, for the thread-visibility of the special variables `%~` and `$_`
We have several examples from https://github.com/jruby/jruby/issues/3031 that seem to exhibit conflicting behavior...or at least the behavior is unexpected in many cases.
```
$ ruby23 -e 'p = proc { p $~; "foo" =~ /foo/ }; Thread.new {p.call}.join; Thread.new{p.call}.join'
nil
nil
$ ruby23 -e 'def foo; proc { p $~; "foo" =~ /foo/ }; end; p = foo; Thread.new {p.call}.join; Thread.new{p.call}.join'
nil
#<MatchData "foo">
$ ruby23 -e 'p = proc { p $~; "foo" =~ /foo/ }; def foo(p); Thread.new {p.call}.join; Thread.new{p.call}.join; end; foo(p)'
nil
#<MatchData "foo">
$ ruby23 -e 'class Foo; P = proc { p $~; "foo" =~ /foo/ }; def foo; Thread.new {P.call}.join; Thread.new{P.call}.join; end; end; Foo.new.foo'
nil
#<MatchData "foo">
$ ruby23 -e 'def foo; p = proc { p $~; "foo" =~ /foo/ }; Thread.new {p.call}.join; Thread.new{p.call}.join; end; foo'
nil
nil
$ ruby23 -e 'def foo; p = proc { p $~; "foo" =~ /foo/ }; bar(p); end; def bar(p); Thread.new {p.call}.join; Thread.new{p.call}.join; end; foo'
nil
#<MatchData "foo">
```
These cases exhibit some oddities in whether $~ (and presumably $_) are shared across threads.
The immediate thought is that they should be both frame and thread-local...but ko1 points out that such a change would break cases like this:
```
def foo
/foo/ =~ 'foo'
Proc.new{
p $~
}
end
Thread.new{
foo.call
}.join
```
So there's a clear conflict here. Users sometimes expect the $~ value to be shared across threads (at least for read, as in ko1's example) and sometimes do not want it shared at all (as in the case of https://github.com/jruby/jruby/issues/3031
Now we discuss.
--
https://bugs.ruby-lang.org/
prev parent reply other threads:[~2021-04-01 20:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <redmine.issue-12689.20160819063718.286@ruby-lang.org>
2021-04-01 20:49 ` [ruby-core:103159] [Ruby master Bug#12689] Thread isolation of $~ and $_ headius
2021-04-01 20:51 ` headius [this message]
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