Bug #21212: IO::Buffer can be freed while its slice is locked

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby 3.5.0dev (2025-04-01T16:11:01Z master 30e5e7c005) +PRISM [x86_64-linux]
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[hanazuki (Kasumi Hanazuki)]

buffer = IO::Buffer.new(100)
slice = buffer.slice

buffer.locked do
  buffer.free rescue p $!  #=> IO::Buffer::LockedError (expected)
end

slice.locked do
  p slice.locked?  #=> true (expected)
  p buffer.locked?  #=> false (what should this be?)

  slice.free rescue p $!  #=> IO::Buffer::LockedError (expected)

  buffer.free  # Should we allow this?

  slice.set_value(:U8, 0, 42)  # raises IO::Buffer::InvalidatedError (surprising!)
end