Issue #21210 has been updated by Eregon (Benoit Daloze). alanwu (Alan Wu) wrote in #note-5:
Looks like the mutable string buffer code paths pin using rb\_str\_locktmp().
Does `rb_str_locktmp()` pin? I couldn't see anything like that from the usage of the flag it sets. ---------------------------------------- Bug #21210: IO::Buffer gets invalidated on GC compaction https://bugs.ruby-lang.org/issues/21210#change-113774 * Author: hanazuki (Kasumi Hanazuki) * Status: Closed * Assignee: ioquatix (Samuel Williams) * ruby -v: ruby 3.5.0dev (2025-04-01T16:11:01Z master 30e5e7c005) +PRISM [x86_64-linux] * Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONTNEED, 3.4: DONTNEED ---------------------------------------- commit:6012145299cfa4ab561360c78710c7f2941a7e9d implemented compaction for `IO::Buffer`. It looks like this doesn't work well with an `IO::Buffer` that shares memory region with a String object. I think the problem is that an `IO::Buffer` holds the raw pointer to the String content, and now the content can be moved by GC when the String is embedded. ```ruby str = +"hello" buf = IO::Buffer.for(str) p buf.valid? GC.verify_compaction_references(expand_heap: true, toward: :empty) p buf.valid? #=> should be true ``` This example should print two trues. Actually: ``` % ./ruby -v --disable-gems test.rb ruby 3.5.0dev (2025-04-01T16:11:01Z master 30e5e7c005) +PRISM [x86_64-linux] true false ``` -- https://bugs.ruby-lang.org/