January 2026 - ruby-core - ml.ruby-lang.org

[ruby-core:124518] [Ruby Bug#21836] RUBY_MN_THREADS deadlock and sleep issues
by jpl-coconut (Jacob Lacouture) 27 Jan '26

27 Jan '26

Issue #21836 has been reported by jpl-coconut (Jacob Lacouture). ---------------------------------------- Bug #21836: RUBY_MN_THREADS deadlock and sleep issues https://bugs.ruby-lang.org/issues/21836 * Author: jpl-coconut (Jacob Lacouture) * Status: Open * ruby -v: ruby 3.4.7 (2025-11-08) +PRISM [aarch64-linux] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- I created a benchmark for the purpose of testing [a fix](https://github.com/ruby/ruby/pull/15840) for [Issue 21685](https://bugs.ruby-lang.org/issues/21685) The benchmark is inline below and saved as 100usec.rb. It should always take just a bit over 10 seconds, regardless of how many cores or threads are assigned. It should look like this: ``` > time taskset --cpu-list 1 ./ruby 100usec.rb 1 real 0m10.130s user 0m0.094s sys 0m0.218s ``` It works fine with MN_THREADS disabled. However, with RUBY_MN_THREADS=1, I see two separate issues. ### Issue #1 is that when the number of cores is set to more than 1, the benchmark completes too fast. These results are consistent across the ruby versions I tried. I did a little debugging and found that the call to `sleep(0.001)` (1ms) is returning after only 0.000005 seconds (5us). ``` > time RUBY_MN_THREADS=1 taskset --cpu-list 1,2 ./ruby 100usec.rb 1 real 0m0.359s user 0m0.075s sys 0m0.134s ``` ### Issue #2 shows up when the number of cores is limited to 1. - On ruby 3.4.7 it runs very slow, about 6x slower than expected. ``` > time RUBY_MN_THREADS=1 taskset --cpu-list 1 ./ruby 100usec.rb 1 real 1m2.277s user 0m0.249s sys 0m0.408s ``` - On ruby 4.0.0-preview2 it usually deadlocks, but sometimes it segfaults. ``` > time RUBY_MN_THREADS=1 taskset --cpu-list 1 ./ruby ruby/100usec.rb 1 [BUG] unreachable ruby 4.0.0preview2 (2025-11-17 master 4fa6e9938c) +MN +PRISM [aarch64-linux] -- Control frame information ----------------------------------------------- -- Threading information --------------------------------------------------- Total ractor count: 1 Ruby thread count for this ractor: 1 -- C level backtrace information ------------------------------------------- [BUG] Illegal instruction at 0x0000ffff93777250 ruby 4.0.0preview2 (2025-11-17 master 4fa6e9938c) +MN +PRISM [aarch64-linux] Crashed while printing bug report Illegal instruction ``` or ``` > time RUBY_MN_THREADS=1 taskset --cpu-list 1 ./ruby ruby/100usec.rb 1 <<DEADLOCK>> ``` ### The benchmark code (100usec.rb) ``` ruby ITRCOUNT = 10000 def inner_test r, w = IO.pipe reader = Thread.new do ITRCOUNT.times.map {|i| r.getbyte } end ITRCOUNT.times.map {|i| sleep 0.0001 w.write('0') } reader.join end def outer_test(count) count.times.map{|j| Thread.new do inner_test end }.each{|t| t.join} end outer_test(ARGV[0].to_i) ``` -- https://bugs.ruby-lang.org/

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[ruby-core:124629] [Ruby Bug#21850] Can't build on FreeBSD/riscv64
by mengzhuo (Meng Zhuo) 27 Jan '26

27 Jan '26

Issue #21850 has been reported by mengzhuo (Meng Zhuo). ---------------------------------------- Bug #21850: Can't build on FreeBSD/riscv64 https://bugs.ruby-lang.org/issues/21850 * Author: mengzhuo (Meng Zhuo) * Status: Open * ruby -v: 3.3.10 * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- I try to build on freebsd/riscv64 poudriere but got this error ``` https://github.com/llvm/llvm-project.git llvmorg-19.1.7-0-gcd708029e0b2) Target: riscv64-unknown-freebsd15.0 Thread model: posix InstalledDir: /nxb-bin/usr/bin generating enc.mk ./enc/make_encmake.rb: [BUG] Segmentation fault at 0x0000000000000000 ruby 3.3.10 (2025-10-23 revision 343ea05002) [riscv64-freebsd15] -- Control frame information ----------------------------------------------- c:0001 p:0000 s:0003 E:000a50 DUMMY [FINISH] -- Threading information --------------------------------------------------- Total ractor count: 1613259843 Ruby thread count for this ractor: 1 ``` ---Files-------------------------------- ruby-3.3.10,1 (1).log (163 KB) -- https://bugs.ruby-lang.org/

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[ruby-core:124627] [Ruby Bug#21849] Ripper.lex emits two `tstring_content` for single string in edge-case
by Earlopain (Earlopain _) 26 Jan '26

26 Jan '26

Issue #21849 has been reported by Earlopain (Earlopain _). ---------------------------------------- Bug #21849: Ripper.lex emits two `tstring_content` for single string in edge-case https://bugs.ruby-lang.org/issues/21849 * Author: Earlopain (Earlopain _) * Status: Open * ruby -v: ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [x86_64-linux] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- ```rb Ripper.lex('"x#$%"') => [[[1, 0], :on_tstring_beg, "\"", BEG], [[1, 1], :on_tstring_content, "x", BEG], [[1, 2], :on_tstring_content, "\#$%", BEG], [[1, 5], :on_tstring_end, "\"", END]] ``` It seems like ripper sees `#$` and assumes that this is bare interpolation. However, `$%` is not a valid global name. So I think it should instead be a single `tstring_content`: ```rb [[[1, 0], :on_tstring_beg, "\"", BEG], [[1, 1], :on_tstring_content, "x\#@%", BEG], [[1, 5], :on_tstring_end, "\"", END]] ``` I stumbled across this in the prism translator for ripper. Prism only emits a single token for the string. -- https://bugs.ruby-lang.org/

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[ruby-core:123920] [Ruby Bug#21715] Miscompilation on x86-64-v2 due to undefined behavior in search_nonascii in string.c
by mjacob (Manuel Jacob) 25 Jan '26

25 Jan '26

Issue #21715 has been reported by mjacob (Manuel Jacob). ---------------------------------------- Bug #21715: Miscompilation on x86-64-v2 due to undefined behavior in search_nonascii in string.c https://bugs.ruby-lang.org/issues/21715 * Author: mjacob (Manuel Jacob) * Status: Open * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- Building the following Dockerfile fails on a x86-64 machine in the last step (running `make` command): ``` FROM opensuse/leap:16.0 RUN zypper --non-interactive install wget make gcc RUN wget 'https://cache.ruby-lang.org/pub/ruby/3.4/ruby-3.4.7.tar.gz' RUN tar xaf ruby-3.4.7.tar.gz WORKDIR ruby-3.4.7/build RUN ../configure RUN make ``` The failing command (during `make`) is: `./miniruby -I../lib -I. -I.ext/common ../tool/mkconfig.rb -arch=x86_64-linux -version=3.4.7 -install_name=ruby -so_name=ruby -unicode_version=15.0.0 -unicode_emoji_version=15.0 > rbconfig.tmp` Excerpt from the crash report: ``` ../tool/mkconfig.rb: [BUG] Segmentation fault at 0x0000000000000000 ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [x86_64-linux] -- Control frame information ----------------------------------------------- c:0001 p:0000 s:0003 E:000ec0 DUMMY [FINISH] -- Threading information --------------------------------------------------- Total ractor count: 1 Ruby thread count for this ractor: 1 -- Machine register context ------------------------------------------------ RIP: 0x0000556c2da74760 RBP: 0x0000000000000027 RSP: 0x00007ffd24a195f0 RAX: 0x0000000000000028 RBX: 0x0000556c64acc420 RCX: 0x0000000000000000 RDX: 0x0000000000000000 RDI: 0x0000000000000014 RSI: 0x00007f49f7d6c123 R8: 0x46ea57707c6b1df2 R9: 0x00007f49f7d6c123 R10: 0x2afb945fcb545f01 R11: 0x0000556c2dc3fe50 R12: 0x00007f49f7d6c263 R13: 0x00007f49f7d6c11b R14: 0x0000556c64bdaa48 R15: 0x00007f49f7d6c25c EFL: 0x0000000000010256 -- C level backtrace information ------------------------------------------- /ruby-3.4.7/build/miniruby(rb_print_backtrace+0x5) [0x556c2db2c1b6] ../vm_dump.c:823 /ruby-3.4.7/build/miniruby(rb_vm_bugreport) ../vm_dump.c:1155 /ruby-3.4.7/build/miniruby(rb_bug_for_fatal_signal+0xf7) [0x556c2d8cdc47] ../error.c:1130 /ruby-3.4.7/build/miniruby(sigsegv+0x42) [0x556c2da58482] ../signal.c:934 /lib64/libc.so.6(__restore_rt+0x0) [0x7f49f7eb2090] /ruby-3.4.7/build/miniruby(search_nonascii+0xcb) [0x556c2da74760] ../string.c:729 /ruby-3.4.7/build/miniruby(coderange_scan) ../string.c:767 /ruby-3.4.7/build/miniruby(rbimpl_fl_unset_raw_raw+0x0) [0x556c2da76874] ../string.c:895 /ruby-3.4.7/build/miniruby(RB_FL_UNSET_RAW) ../include/ruby/internal/fl_type.h:669 /ruby-3.4.7/build/miniruby(RB_ENC_CODERANGE_SET) ../include/ruby/internal/encoding/coderange.h:131 /ruby-3.4.7/build/miniruby(enc_coderange_scan) ../string.c:911 /ruby-3.4.7/build/miniruby(rb_enc_str_coderange) ../string.c:910 /ruby-3.4.7/build/miniruby(is_ascii_string+0x8) [0x556c2da7697e] ../internal/string.h:151 /ruby-3.4.7/build/miniruby(str_do_hash) ../string.c:393 /ruby-3.4.7/build/miniruby(register_fstring) ../string.c:554 /ruby-3.4.7/build/miniruby(rb_enc_literal_str+0x87) [0x556c2da94bb7] ../string.c:12546 /ruby-3.4.7/build/miniruby(parse_static_literal_string+0x38) [0x556c2d875991] ../prism_compile.c:312 /ruby-3.4.7/build/miniruby(pm_compile_node) ../prism_compile.c:10321 /ruby-3.4.7/build/miniruby(pm_compile_node+0x2e65) [0x556c2d875aa5] ../prism_compile.c:10309 /ruby-3.4.7/build/miniruby(pm_compile_conditional+0x18c) [0x556c2d88cfcc] ../prism_compile.c:1053 /ruby-3.4.7/build/miniruby(pm_compile_node+0x42e1) [0x556c2d876f21] ../prism_compile.c:9355 /ruby-3.4.7/build/miniruby(pm_setup_args_core+0xe4) [0x556c2d884304] ../prism_compile.c:1792 /ruby-3.4.7/build/miniruby(pm_setup_args+0x98) [0x556c2d884e98] ../prism_compile.c:1979 /ruby-3.4.7/build/miniruby(pm_compile_call+0x307) [0x556c2d885cf7] ../prism_compile.c:3673 /ruby-3.4.7/build/miniruby(pm_compile_call_node+0x2c6) [0x556c2d872326] ../prism_compile.c:7403 /ruby-3.4.7/build/miniruby(pm_compile_node+0x39dc) [0x556c2d87661c] ../prism_compile.c:8775 /ruby-3.4.7/build/miniruby(pm_compile_node+0x2e65) [0x556c2d875aa5] ../prism_compile.c:10309 /ruby-3.4.7/build/miniruby(pm_compile_conditional+0x18c) [0x556c2d88cfcc] ../prism_compile.c:1053-march=x86-64-v2 /ruby-3.4.7/build/miniruby(pm_compile_node+0x42e1) [0x556c2d876f21] ../prism_compile.c:9355 /ruby-3.4.7/build/miniruby(pm_compile_node+0x2e3a) [0x556c2d875a7a] ../prism_compile.c:10307 /ruby-3.4.7/build/miniruby(pm_compile_scope_node+0x104a) [0x556c2d88f5da] ../prism_compile.c:6991 /ruby-3.4.7/build/miniruby(pm_compile_node+0x35c9) [0x556c2d876209] ../prism_compile.c:10180 /ruby-3.4.7/build/miniruby(APPEND_LIST+0x0) [0x556c2d891e60] ../prism_compile.c:10481 /ruby-3.4.7/build/miniruby(pm_iseq_compile_node) ../prism_compile.c:10485 /ruby-3.4.7/build/miniruby(pm_iseq_new_with_opt_try+0x10) [0x556c2d94c790] ../iseq.c:1042 /ruby-3.4.7/build/miniruby(rb_protect+0xd6) [0x556c2d8db9c6] ../eval.c:1054 /ruby-3.4.7/build/miniruby(pm_iseq_new_with_opt+0x177) [0x556c2d9525c7] ../iseq.c:1095 /ruby-3.4.7/build/miniruby(pm_iseq_new_main+0x85) [0x556c2d952895] ../iseq.c:943 /ruby-3.4.7/build/miniruby(process_options+0x12fd) [0x556c2da519cd] ../ruby.c:2616 /ruby-3.4.7/build/miniruby(ruby_process_options+0x157) [0x556c2da52657] ../ruby.c:3174 /ruby-3.4.7/build/miniruby(ruby_options+0x97) [0x556c2d8da977] ../eval.c:117 /ruby-3.4.7/build/miniruby(rb_main+0x19) [0x556c2d7eb578] ../prism/prism.c:21769 /ruby-3.4.7/build/miniruby(main) ../main.c:68 /lib64/libc.so.6(__libc_start_call_main+0x82) [0x7f49f7e9b340] /lib64/libc.so.6(__libc_start_main+0x8b) [0x7f49f7e9b409] /ruby-3.4.7/build/miniruby(_start+0x25) [0x556c2d7eb5c5] ../main.c:69 ``` The failing instruction at 0x556c2da74760 is: `movdqa xmm0, XMMWORD PTR [rsi+rcx*1]`. At this place, register `rsi` contains 0x7f49f7d6c123, which is the value 0x7f49f7d6c11b of parameter `p` of the function `search_nonascii` + 8, and register `rcx` contains 0. So, the whole instruction means “[move aligned packed integer values](https://www.felixcloutier.com/x86/movdqa:vmovdqa32:vmovdqa64) from memory at 0x7f49f7d6c123 to register `xmm0`”. The segmentation fault happened because the address is expected to be aligned on a 16-byte boundary, but it is not. The instruction is part of a loop at https://github.com/ruby/ruby/blob/v3_4_7/string.c#L728 that gets auto-vectorized by GCC. On x86-64, * `UNALIGNED_WORD_ACCESS` is `1` * `p` doesn’t get aligned to anything because of `#if !UNALIGNED_WORD_ACCESS` in line 700 * `aligned_ptr(value)` is expanded to `(uintptr_t *)(value)` according to line 723 * `p` is therefore casted to type `uintptr_t *` in line 725 * `uintptr_t` is typedefed to `unsigned long int`, which has alignment of 8 bytes In result, a pointer `p` to potentially unaligned memory is casted to a pointer to a type with alignment of 8 bytes. That is undefined behavior according to C99 6.3.2.3p7: “A pointer to an object or incomplete type may be converted to a pointer to a different object or incomplete type. If the resulting pointer is not correctly aligned for the pointed-to type, the behavior is undefined.”. Compilers can utilize this rule to make the assumption that the pointed-to memory has alignment of 8 bytes. In this case, the GCC loop auto-vectorizer adds code to align the assumedly 8 bytes aligned address to 16 bytes alignment. A subsequent instruction assuming 16 bytes alignment can therefore fail. I could reproduce this crash only on openSUSE Leap 16.0, but not openSUSE Leap 15.6, openSUSE Tumbleweed or Arch Linux, because only the former configured GCC to default to emitting code requiring x86-64-v2. When passing `-march=x86-64-v2` in CFLAGS, the crash happens on all these distributions. -- https://bugs.ruby-lang.org/

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[ruby-core:124475] [Ruby Bug#21832] segfault with argument forwarding, when combined with splat & positional arg
by inopinatus (Joshua GOODALL) 25 Jan '26

25 Jan '26

Issue #21832 has been reported by inopinatus (Joshua GOODALL). ---------------------------------------- Bug #21832: segfault with argument forwarding, when combined with splat & positional arg https://bugs.ruby-lang.org/issues/21832 * Author: inopinatus (Joshua GOODALL) * Status: Open * ruby -v: ruby 4.1.0dev (2026-01-11T15:46:56Z master 61c372a1b7) +PRISM [arm64-darwin24] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- A crash occurs when combining (...) arg forwarding, a positional argument, and an array splat. Found with 4.0.0 release, verified on 3.4.8 and 4.1.0dev, does not occur on 3.3.10. One-line crash test: ``` ruby ./ruby -e 'def target(*args) = args; def x = [1]; def forwarder(...); target(*x, 2, ...); end; forwarder(3)' ``` test builds were: * Ruby 4.1.0dev w/clang-1700.6.3.2 on arm64 (macOS Sequoia 15.7.1) * Ruby 3.4.8 w/gcc 13.3.0 on x86_64 (Ubuntu 24.04 LTS) longer test case: ``` ruby class Test def stdargs %w(--verbose) end def func(*args) puts "args: #{args.inspect}" end def test1(...) func("abc", ...) end def test2(...) func(stdargs, "abc", ...) end def test3(...) func(*stdargs, "abc") end def test4(...) func(*stdargs, ...) end def test5(...) func(*stdargs, "abc", ...) end end o = Test.new o.test1("T1") #=> args: ["abc", "T1"] o.test2("T2") #=> args: [["foo"], "abc", "T2"] o.test3("T3") #=> args: ["foo", "abc"] o.test4("T4") #=> args: ["foo", "T4"] o.test5("T5") #=> Expected: ["foo", "abc", "T5"] Actual: crash ``` Crash output: ``` [505] (master) joshua@coltrane:~/src/ruby-src$ ./ruby crash.rb `RubyGems' were not loaded. `error_highlight' was not loaded. `did_you_mean' was not loaded. `syntax_suggest' was not loaded. args: ["abc", "T1"] args: [["--verbose"], "abc", "T2"] args: ["--verbose", "abc"] args: ["--verbose", "T4"] crash.rb:28: [BUG] Segmentation fault at 0x0000000000000000 ruby 4.1.0dev (2026-01-11T15:46:56Z master 61c372a1b7) +PRISM [arm64-darwin24] -- Crash Report log information -------------------------------------------- See Crash Report log file in one of the following locations: * ~/Library/Logs/DiagnosticReports * /Library/Logs/DiagnosticReports for more details. Don't forget to include the above Crash Report log file in bug reports. -- Control frame information ----------------------------------------------- c:0003 p:0013 s:0017 e:000012 l:y b:0001 METHOD crash.rb:28 c:0002 p:0059 s:0007 E:002508 l:n b:---- EVAL crash.rb:38 [FINISH] c:0001 p:0000 s:0003 E:000010 l:y b:---- DUMMY [FINISH] -- Ruby level backtrace information ---------------------------------------- crash.rb:38:in '<main>' crash.rb:28:in 'test5' -- Threading information --------------------------------------------------- Total ractor count: 1 Ruby thread count for this ractor: 1 -- Machine register context ------------------------------------------------ x0: 0x0000000160028078 x1: 0x0000000000000000 x2: 0x0000000000000010 x3: 0x0000000160028078 x4: 0x0000000000000000 x5: 0x000000016d97a670 x6: 0x000000016d97a648 x7: 0x000000016d97a598 x18: 0x0000000000000000 x19: 0x0000000000000000 x20: 0x000000016d97a648 x21: 0x0000000102e9da38 x22: 0x0000000160127f58 x23: 0x000000016d97a670 x24: 0x0000000160028078 x25: 0x000092d100100003 x26: 0x0000000160028060 x27: 0x0000000000000001 x28: 0x0000000000000001 lr: 0x00000001026eab50 fp: 0x000000016d97a5e0 sp: 0x000000016d97a560 -- C level backtrace information ------------------------------------------- /Users/joshua/src/ruby-src/ruby(rb_vm_bugreport+0xbc8) [0x10271b60c] /Users/joshua/src/ruby-src/vm_dump.c:1450 /Users/joshua/src/ruby-src/ruby(rb_vm_bugreport) (null):0 /Users/joshua/src/ruby-src/ruby(rb_bug_for_fatal_signal+0x10c) [0x10254092c] /Users/joshua/src/ruby-src/error.c:1131 /Users/joshua/src/ruby-src/ruby(sigsegv+0x90) [0x102671e70] /Users/joshua/src/ruby-src/signal.c:948 /usr/lib/system/libsystem_platform.dylib(_sigtramp+0x38) [0x196be16a4] /Users/joshua/src/ruby-src/ruby(RB_FL_TEST_RAW+0x0) [0x1026eab50] ./include/ruby/internal/memory.h:759 /Users/joshua/src/ruby-src/ruby(RB_FL_ANY_RAW) ./include/ruby/internal/fl_type.h:466 /Users/joshua/src/ruby-src/ruby(rb_array_len) ./include/ruby/internal/core/rarray.h:259 /Users/joshua/src/ruby-src/ruby(vm_caller_setup_fwd_args) ./vm_insnhelper.c:3410 /Users/joshua/src/ruby-src/ruby(vm_exec_core+0x12f0) [0x1026ed304] /Users/joshua/src/ruby-src/insns.def:877 /Users/joshua/src/ruby-src/ruby(rb_vm_exec+0x284) [0x1026ea428] /Users/joshua/src/ruby-src/vm.c:2798 /Users/joshua/src/ruby-src/ruby(rb_ec_exec_node+0x8c) [0x10254bb84] /Users/joshua/src/ruby-src/eval.c:283 /Users/joshua/src/ruby-src/ruby(ruby_run_node+0x4c) [0x10254baa4] /Users/joshua/src/ruby-src/eval.c:321 /Users/joshua/src/ruby-src/ruby(rb_main+0x1c) [0x102484980] ./main.c:42 /Users/joshua/src/ruby-src/ruby(main) ./main.c:62 ``` -- https://bugs.ruby-lang.org/

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[ruby-core:124366] [Ruby Bug#21807] ArgumentError is reported when forwarding arguments to method with intermediate optional arguments
by taichi730 (Taichi Ishitani) 25 Jan '26

25 Jan '26

Issue #21807 has been reported by taichi730 (Taichi Ishitani). ---------------------------------------- Bug #21807: ArgumentError is reported when forwarding arguments to method with intermediate optional arguments https://bugs.ruby-lang.org/issues/21807 * Author: taichi730 (Taichi Ishitani) * Status: Open * ruby -v: 3.4.8 * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- In Ruby 3.4.x, @ArgumentError@ is reported when forwarding arguments to a method with intermediate optional arguments. How to reproduce: Execute sample below. ``` ruby class Foo def foo(a = nil, b) p a, b end end class Bar def initialize @foo = Foo.new end def bar(...) @foo.foo(...) @foo.foo(...) end end class Baz def initialize @bar = Bar.new end def baz(_a, ...) @bar.bar(...) end end puts RUBY_VERSION baz = Baz.new baz.baz(0, 1) ``` output: <pre> $ RBENV_VERSION=3.4.8 ruby test.rb 3.4.8 nil 1 test.rb:2:in 'foo': wrong number of arguments (given 0, expected 1..2) (ArgumentError) from test.rb:14:in 'Bar#bar' from test.rb:24:in 'Baz#baz' </pre> <pre> $ RBENV_VERSION=3.4.1 ruby test.rb 3.4.1 nil 1 test.rb:2:in 'foo': wrong number of arguments (given 0, expected 1..2) (ArgumentError) from test.rb:14:in 'Bar#bar' from test.rb:24:in 'Baz#baz' </pre> For other Ruby verions (e.g. 4.0.0, 3.3.0), no error is reported. <pre> $ RBENV_VERSION=4.0.0 ruby test.rb 4.0.0 nil 1 nil 1 </pre> <pre> $ RBENV_VERSION=3.3.0 ruby test.rb 3.3.0 nil 1 nil 1 </pre> -- https://bugs.ruby-lang.org/

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[ruby-core:121993] [Ruby Bug#21326] Instruction generation differences between parse.y and prism for `def a(x, ...); b(...); end`
by zenspider (Ryan Davis) 25 Jan '26

25 Jan '26

Issue #21326 has been reported by zenspider (Ryan Davis). ---------------------------------------- Bug #21326: Instruction generation differences between parse.y and prism for `def a(x, ...); b(...); end` https://bugs.ruby-lang.org/issues/21326 * Author: zenspider (Ryan Davis) * Status: Open * ruby -v: ruby 3.5.0dev * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- Diff instructions using: ```sh DUMP="puts RubyVM::InstructionSequence.compile(ARGV.first).disasm.gsub(/^\d+ /, '')" RUBY="def a(x, ...); b(...); end" env -u RUBYOPT \ diff -U99 \ <(./build/ruby -v --parser=parse.y -e "$DUMP" "$RUBY" 2>/dev/null) \ <(./build/ruby -v --parser=prism -e "$DUMP" "$RUBY" 2>/dev/null) ``` shows: ```diff --- /dev/fd/63 2025-05-10 14:46:37 +++ /dev/fd/62 2025-05-10 14:46:37 @@ -1,17 +1,18 @@ -ruby 3.5.0dev (2025-05-10T17:32:21Z master 98667f82d2) +GC [arm64-darwin24] +ruby 3.5.0dev (2025-05-10T17:32:21Z master 98667f82d2) +PRISM +GC [arm64-darwin24] == disasm: #<ISeq:<compiled>@<compiled>:1 (1,0)-(1,26)> definemethod :a, a ( 1)[Li] putobject :a leave == disasm: #<ISeq:a@<compiled>:1 (1,0)-(1,26)> local table (size: 5, argc: 1 [opts: 0, rest: 1, post: 0, block: 3, kw: -1@-1, kwrest: 2]) [ 5] x@0<Arg> [ 4] "*"@1<AnonRest>[ 3] "**"@2<AnonKwrest>[ 2] "&"@3<Block>[ 1] "..."@4 putself ( 1)[LiCa] getlocal_WC_0 "*"@1 -splatarray false +splatarray true getlocal_WC_0 "**"@2 getblockparamproxy "&"@3, 0 splatkw -send <calldata!mid:b, argc:2, ARGS_SPLAT|ARGS_BLOCKARG|FCALL|KW_SPLAT>, nil +splatkw +send <calldata!mid:b, argc:2, ARGS_SPLAT|ARGS_SPLAT_MUT|ARGS_BLOCKARG|FCALL|KW_SPLAT>, nil leave [Re] ``` PR here: https://github.com/ruby/ruby/pull/13299 goes back to at least 3.4. -- https://bugs.ruby-lang.org/

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[ruby-core:124616] [Ruby Bug#21848] GC compaction freezes during code reload with 100% CPU in rb_vm_ci_free -> st_general_delete
by henrik (Henrik A) 24 Jan '26

24 Jan '26

Issue #21848 has been reported by henrik (Henrik A). ---------------------------------------- Bug #21848: GC compaction freezes during code reload with 100% CPU in rb_vm_ci_free -> st_general_delete https://bugs.ruby-lang.org/issues/21848 * Author: henrik (Henrik A) * Status: Open * ruby -v: ruby 4.0.1 (2026-01-13 revision e04267a14b) +PRISM [arm64-darwin24] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- Ruby 4.0.1 freezes with 100% CPU usage when garbage collection runs during Rails code reloading (hot reload in development). The process becomes unresponsive and requires kill -9 to terminate. Environment: - Ruby: 4.0.1 (Homebrew, ARM64) - Platform: macOS 15.6.1 (Darwin 24.6.0, Apple Silicon) - Rails: 8.x with Puma 7.2.0 - Mode: Development with code reloading enabled Steps to reproduce: 1. Run a Rails application with Puma in development mode (bundle exec rails server -e development -b 0.0.0.0) 2. Make a several code change to trigger hot reload, reload the site in the browser in between 3. Process freezes with ~100% CPU Expected behavior: Code reloads successfully, GC completes normally. Actual behavior: Process freezes indefinitely at 100% CPU. Stack trace from sample shows GC stuck in hash table lookup while freeing VM call info: ``` gc_sweep (in libruby.4.0.dylib) gc_compact_plane gc_sweep_page gc_sweep_plane rb_gc_obj_free_vm_weak_references rb_vm_ci_free st_general_delete find_table_bin_ind vm_ci_hash_cmp <-- stuck here, spinning ``` Full relevant stack (Puma worker thread): ``` Thread: puma srv tp 005 rb_ary_each -> rb_yield -> invoke_block_from_c_bh -> rb_vm_exec -> int_upto -> rb_yield (nested loops) -> vm_search_method_slowpath0 -> rb_vm_search_method_slowpath -> newobj_of -> newobj_cache_miss -> gc_continue -> gc_sweep -> gc_compact_plane -> gc_sweep_page -> gc_sweep_plane -> rb_gc_obj_free_vm_weak_references -> rb_vm_ci_free -> st_general_delete -> find_table_bin_ind -> vm_ci_hash_cmp ``` Workaround: Disabling auto-compaction prevents the freeze: GC.auto_compact = false Analysis: The freeze occurs during GC sweep/compaction when freeing cached VM call info entries (rb_vm_ci_free). This is triggered by code reloading which invalidates method caches. The GC appears to get stuck in an infinite loop or extremely slow operation in find_table_bin_ind while looking up entries in the call info hash table. ---Files-------------------------------- rails_stuck.txt (159 KB) -- https://bugs.ruby-lang.org/

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[ruby-core:124599] [Ruby Feature#21846] Add a fast path for GC sweeping
by eightbitraptor (Matt V-H) 23 Jan '26

23 Jan '26

Issue #21846 has been reported by eightbitraptor (Matt V-H). ---------------------------------------- Feature #21846: Add a fast path for GC sweeping https://bugs.ruby-lang.org/issues/21846 * Author: eightbitraptor (Matt V-H) * Status: Open ---------------------------------------- [Github PR 15885](https://github.com/ruby/ruby/pull/15885) ## Summary This proposal adds a fast path through the garbage collector's sweep phase that skips expensive cleanup operations for objects that don't require them. Simple embedded objects without external resources, finalizers, or weak references are added directly to the freelist, resulting in a 20-40% reduction in sweep time and 1-2% improvement in overall application performance. ## Background Ruby's garbage collector currently uses a single code path for sweeping all objects. During the sweep phase, every unmarked object goes through `rb_gc_obj_free_vm_weak_references` to clean up entries in the object_id table (`id2ref_tbl`) and generic fields table, followed by `rb_gc_obj_free` for type-specific cleanup and memory deallocation. This is necessary for objects with external resources, but a lot of objects created are "simple" - they have no external allocations, no registered object_id, no generic ivars, and no finalizers. For these simple objects, the sweep phase does significant work even though there's nothing to clean up. Every object is checked against the `id2ref_tbl` table (even if `ObjectSpace._id2ref` was never called), they're checked for finalizers, and they go through type-specific free functions that often just return immediately. In applications that allocate many temporary objects, this overhead accumulates significantly. ## Proposal A new predicate function `gc_sweep_fast_path_p` determines whether an object can skip the expensive cleanup calls. Objects eligible for the fast path are added directly to the freelist after clearing the write barrier unprotected bit. Two conditions always require the slow path: 1. The object has a finalizer (`FL_FINALIZE` flag is set) 2. The object has an observed `object_id` stored in the `id2ref_tbl` (checked via `rb_shape_has_object_id`) If neither condition applies, we move on to some type specific flag checks We use the fast path in these cases: * `T_OBJECT`: Embedded objects only (no heap-allocated instance variable array) * `T_STRING`: Embedded strings that aren't frozen * `T_ARRAY`: Embedded arrays * `T_HASH`: Embedded hashes (ie. no external `st_table`) * `T_BIGNUM`: Embedded bignums * `T_STRUCT`: Embedded structs * `T_FLOAT`, `T_RATIONAL`, `T_COMPLEX` * `T_DATA`: TypedData that is embedded with a NULL or `RUBY_DEFAULT_FREE` dfree function * `T_IMEMO`: Safe subtypes only (constcache, cref, ifunc, memo, svar, throw_data) For all the above types we'll also check whether any generic ivars are registered in the `generic_fields_tbl`. If they have generic ivars set, then we'll use the slow path to clean them up. All other types use the slow path. ### Compatibility Currently this patch is is disabled for modular GC builds (`BUILDING_MODULAR_GC`) because we need access to the `id2ref_tbl`, and I haven't pushed it through the GC API. ## Evaluation ### Benchmark Results All benchmarks were run on an Amazon c5.metal bare-metal VM with turbo boost and ASLR disabled, CPU frequency locked and using the performance governor, and pinned to a single core using `taskset`. GC-specific benchmarks show significant sweep time improvements: ``` Benchmark │ Wall(B) Sweep(B) Mark(B) │ Wall(E) Sweep(E) Mark(E) │ Wall Δ Sweep Δ ───────────────┼────────────────────────────────┼────────────────────────────────┼────────────────── null │ 0.000s 1ms 4ms │ 0.000s 1ms 4ms │ 0% 0% hash1 │ 4.330s 875ms 46ms │ 3.960s 531ms 44ms │ +8.6% +39.3% hash2 │ 6.356s 243ms 988ms │ 6.298s 176ms 1.03s │ +0.9% +27.6% rdoc │ 37.337s 2.42s 1.09s │ 36.678s 2.11s 1.20s │ +1.8% +13.1% binary_trees │ 3.366s 426ms 252ms │ 3.082s 275ms 239ms │ +8.4% +35.4% ring │ 5.252s 14ms 2.47s │ 5.327s 12ms 2.43s │ -1.4% +14.3% redblack │ 2.966s 28ms 41ms │ 2.940s 21ms 38ms │ +0.9% +25.0% ───────────────┼────────────────────────────────┼────────────────────────────────┼────────────────── Legend: (B) = Baseline, (E) = Experiment, Δ = improvement (positive = faster) Wall = total wallclock, Sweep = GC sweeping time, Mark = GC marking time Times are median of 3 runs ``` Application benchmarks (YJIT enabled): ``` -------------- ----------- ---------- --------------- ---------- ------------------ ----------------- bench master (ms) stddev (%) experiment (ms) stddev (%) experiment 1st itr master/experiment activerecord 132.5 0.9 132.5 1.0 1.056 1.001 chunky-png 577.2 0.4 580.1 0.4 0.994 0.995 erubi-rails 902.9 0.2 894.3 0.2 1.040 1.010 hexapdf 1763.9 3.3 1760.6 3.7 1.027 1.002 liquid-c 56.9 0.6 56.7 1.4 1.004 1.003 liquid-compile 46.3 2.1 46.1 2.1 1.005 1.004 liquid-render 77.8 0.8 75.1 0.9 1.023 1.036 mail 114.7 0.4 113.0 1.4 1.054 1.015 psych-load 1635.4 1.4 1625.9 0.5 0.988 1.006 railsbench 1685.4 2.4 1650.1 2.0 0.989 1.021 rubocop 133.5 8.1 130.3 7.8 1.002 1.024 ruby-lsp 140.3 1.9 137.5 1.8 1.007 1.020 sequel 64.6 0.7 63.9 0.7 1.003 1.011 shipit 1196.2 4.3 1181.5 4.2 1.003 1.012 -------------- ----------- ---------- --------------- ---------- ------------------ ----------------- Legend: - master/experiment: ratio of master/experiment time. Higher is better for experiment. Above 1 represents a speedup. ``` ### Analysis The GC benchmarks show sweep time improvements of 13-39% across workloads, with the largest gains in hash-heavy and tree-based benchmarks where many simple embedded objects are allocated. The `hash1` benchmark shows nearly 40% faster sweeping, translating to 8.6% wall clock improvement. Application benchmarks show modest but consistent 1-2% improvements, with `railsbench` showing a 2.1% speedup. The improvement is smaller for applications because sweep time is typically a small fraction of total execution time, but the gains are additive with other optimizations. The `ring` benchmark shows a small regression in wall time despite faster sweeping, likely due to measurement noise or allocation pattern differences. The sweep improvement (+14.3%) is still present. The conservative nature of the fast path means some objects that could theoretically skip cleanup will still use the slow path. For example, a T_STRING with generic instance variables added via `instance_variable_set` will use the slow path even though the string content itself is embedded. This is intentional - We'd rather miss an optimisation opportunity than cause a memory leak. -- https://bugs.ruby-lang.org/

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[ruby-core:116935] [Ruby master Bug#18743] Enumerator#next / peek re-use each others stacktraces
by nagachika (Tomoyuki Chikanaga) 22 Jan '26

22 Jan '26

Issue #18743 has been updated by nagachika (Tomoyuki Chikanaga). Backport changed from 3.0: REQUIRED, 3.1: REQUIRED, 3.2: REQUIRED to 3.0: REQUIRED, 3.1: REQUIRED, 3.2: DONE ruby_3_2 5e4606423da96c2e26b00981c22bddfce0d970bf merged revision(s) f15123c34ce80f3928612befe2a9aaf4c9d27fda. ---------------------------------------- Bug #18743: Enumerator#next / peek re-use each others stacktraces https://bugs.ruby-lang.org/issues/18743#change-106970 * Author: sos4nt (Stefan Schüßler) * Status: Closed * Assignee: ko1 (Koichi Sasada) * Backport: 3.0: REQUIRED, 3.1: REQUIRED, 3.2: DONE ---------------------------------------- I encountered an odd behavior. If I rescue the `StopIteration` exception from `peek` and call `next` afterwards: (or vice-versa) ```ruby # enum.rb # 1 # 2 enum = [].each # 3 enum.peek rescue nil # 4 enum.next # 5 ``` it will show the stacktrace from the rescued `peek` call: ``` $ ruby enum.rb enum.rb:4:in `peek': iteration reached an end (StopIteration) from enum.rb:4:in `<main>' ``` Whereas the error should refer to `next` on line number 5. The same happens when calling `peek` after `next` or when having muliple `peek` / `next` calls: ```ruby # enum.rb # 1 # 2 enum = [].each # 3 enum.peek rescue nil # 4 enum.next rescue nil # 5 enum.peek rescue nil # 6 puts "line #{__LINE__}" # 7 enum.next # 8 ``` The stacktrace from the first (rescued) `peek` or `next` call will be shown which doesn't reflect the actual error location: ``` $ ruby enum.rb line 7 enum.rb:4:in `peek': iteration reached an end (StopIteration) from enum.rb:4:in `<main>' ``` This is very confusing when debugging code. ---Files-------------------------------- 01-Recreate-stacktrace-enumerator.patch (1.29 KB) -- https://bugs.ruby-lang.org/

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