Bug #17188: Freeze Encoding objects for Ractor

• Status: Closed
• Assignee: ko1 (Koichi Sasada)
• Target version: 3.0
• ruby -v: ruby 3.0.0preview1 (2020-09-25 master 0096d2b895) [x86_64-linux]
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN

[Eregon (Benoit Daloze)]

Currently Encoding objects are not frozen:

$ ruby -ve 'p Encoding::US_ASCII.frozen?'
ruby 3.0.0dev (2020-09-25T08:28:42Z master 81dc37b1b4) [x86_64-linux]
false

That means they cannot be accessed in a Ractor:

irb(main):001:0> Encoding::US_ASCII
=> #<Encoding:US-ASCII>

irb(main):002:0> Ractor.new { Encoding::US_ASCII }
<internal:ractor>:38: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
=> #<Ractor:#2 (irb):2 running>
#<Thread:0x00005567521d81e8 run> terminated with exception (report_on_exception is true):
(irb):2:in `block in irb_binding': can not access non-sharable objects in constant Encoding::US_ASCII by non-main Ractor. (NameError)

And Ractor.new { p "".encoding } is likely violating the Ractor guarantees.

I think we can make all Encoding instances frozen.

Making them frozen is also useful for code sharing, which TruffleRuby aims to support via the GraalVM Engine/Context API.

cc @ko1 (Koichi Sasada)

[Eregon (Benoit Daloze)]

• Tracker changed from Feature to Bug
• Assignee set to ko1 (Koichi Sasada)
• ruby -v set to ruby 3.0.0preview1 (2020-09-25 master 0096d2b895) [x86_64-linux]
• Backport set to 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN

Changing this to a bug, because it can cause unsafe sharing:

irb(main):003:0> Encoding::UTF_8.instance_variable_set(:@foo, Object.new)
=> #<Object:0x00005596506b8a28>
irb(main):004:0> Ractor.new { p "b".encoding.instance_variable_get("@foo") }
#<Object:0x00005596506b8a28>

[ko1 (Koichi Sasada)]

• Status changed from Open to Closed

Applied in changeset git|102c2ba65f1fa2a6cdbaaa7d2b466aabfc50e5d7.

---

freeze Encoding objects

Encoding objects can be accessed in multi-ractors and there is no
state to mutate. So we can mark it as frozen and shareable.
[Bug #17188]