Bug #7678: $_ and $~ are shared across Fibers halfway

• Status: Closed
• Assignee: -
• Target version: 2.0.0
• ruby -v: r38748

[nobu (Nobuyoshi Nakada)]

=begin
((|$_|)) and ((|$~|)) have thread local method scope, but are shared across fibers in same thread.

$ ./ruby -v -e '/a/ =~ "a"; p $; Fiber.new{/b/="b"; p $}.resume; p $'
ruby 2.0.0dev (2013-01-09 trunk 38748) [x86_64-darwin11]
#<MatchData "a">
#<MatchData "b">
#<MatchData "b">

But, it is cleared at (({Fiber.start})).

$ ./ruby -v -e '/a/ =~ "a"; p $; Fiber.new{p $}.resume; p $~'
ruby 2.0.0dev (2013-01-09 trunk 38748) [x86_64-darwin11]
#<MatchData "a">
nil
nil

These two behaviors seem mismatched. I think:

• If they should be shared, then the latter example should show same
  (({MatchData})) 3 times.

• If they should be cleared at starting fibers, those variables in the
  original fiber should be unchanged.
  =end

[ko1 (Koichi Sasada)]

• Target version set to 2.0.0

Nobu, should we finish this issue before 2.0?

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)

I think this is one of undefined behaviors, so it would cause no compatibility issue.
We can fix it once we decide which is more desirable, shared between fibers or separate per fibers.

[ko1 (Koichi Sasada)]

(2013/01/29 14:19), nobu (Nobuyoshi Nakada) wrote:

I think this is one of undefined behaviors, so it would cause no compatibility issue.
We can fix it once we decide which is more desirable, shared between fibers or separate per fibers.

I asked matz about it and his choice is separate between Fibers.

--
// SASADA Koichi at atdot dot net

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r38981.
Nobuyoshi, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

cont.c: fiber local svar

• cont.c (cont_restore_thread): svar should be separate per fibers.
  [ruby-core:51331] [Bug #7678]