From: "ianks (Ian Ker-Seymer) via ruby-core" <ruby-core@...>
Date: 2023-05-03T03:01:52+00:00
Subject: [ruby-core:113398] [Ruby master Feature#19627] Add a way to detect if the Ruby VM is running in C API

Issue #19627 has been updated by ianks (Ian Ker-Seymer).





For documentations sake, [he's a real world reproduction of this issue that happens when calling TLS destructors](https://github.com/bytecodealliance/wasmtime-rb/actions/runs/4850597226/jobs/8643651566?pr=181). In Ruby < 3.3-dev, I'm able to avoid this by checking the hidden `ruby_current_vm_ptr` symbol so the code won't segfault after VM shutdown.





```

-- C level backtrace information -------------------------------------------

/home/runner/.rubies/ruby-head/lib/libruby.so.3.3(rb_print_backtrace+0xd) [0x7f360aab3a3f] /home/runner/work/ruby-dev-builder/ruby-dev-builder/vm_dump.c:785

/home/runner/.rubies/ruby-head/lib/libruby.so.3.3(rb_vm_bugreport) /home/runner/work/ruby-dev-builder/ruby-dev-builder/vm_dump.c:1101

/home/runner/.rubies/ruby-head/lib/libruby.so.3.3(rb_bug_for_fatal_signal+0xf4) [0x7f360a8b8c94] /home/runner/work/ruby-dev-builder/ruby-dev-builder/error.c:814

/home/runner/.rubies/ruby-head/lib/libruby.so.3.3(sigsegv+0x4d) [0x7f360a9feecd] /home/runner/work/ruby-dev-builder/ruby-dev-builder/signal.c:964

/lib/x86_64-linux-gnu/libc.so.6(0x7f360a413520) [0x7f360a413520]

/home/runner/.rubies/ruby-head/lib/libruby.so.3.3(rb_gc_adjust_memory_usage+0xe) [0x7f360a8dedbe] /home/runner/work/ruby-dev-builder/ruby-dev-builder/gc.c:12743

/lib/x86_64-linux-gnu/libc.so.6(__call_tls_dtors+0x3f) [0x7f360a416d9f]

/lib/x86_64-linux-gnu/libc.so.6(0x7f360a4165c9) [0x7f360a4165c9]

/lib/x86_64-linux-gnu/libc.so.6(on_exit+0x20) [0x7f360a416610]

/lib/x86_64-linux-gnu/libc.so.6(0x7f360a3fad97) [0x7f360a3fad97]

/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80) [0x7f360a3fae40]

[0x55e16aa391d5]

```





----------------------------------------

Feature #19627: Add a way to detect if the Ruby VM is running in C API

https://bugs.ruby-lang.org/issues/19627#change-102969



* Author: ianks (Ian Ker-Seymer)

* Status: Open

* Priority: Normal

----------------------------------------

Currently, there is no supported way to check if the Ruby VM has been shut down. There are a couple of workarounds that I know of:



1. Setup an exit handler which sets a global variable (like I did in https://github.com/tmm1/stackprof/pull/200).

2. In Ruby 2.4 thru 3.2, you could check the hidden `ruby_vm_global_ptr != NULL`.



For my use, in rb-sys there is a feature to automatically report Rust memory allocations via `rb_gc_adjust_memory_usage`. However, there is a bug that can cause processes to deadlock and/or segfault if a Rust destructor gets called after the VM quits (which can happen in Rust background threads). Currently, I don���t think there���s a way to safely make this feature work. (https://github.com/oxidize-rb/rb-sys/pull/205)



It would be nice to have an official way to know if the Ruby VM is available, basically just a `ruby_current_vm_ptr != null`. Thoughts?











-- 

https://bugs.ruby-lang.org/

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