December 2025 - ruby-core - ml.ruby-lang.org

[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:124270] [Ruby Bug#21787] `IO::Buffer` buffer overf
by nobu (Nobuyoshi Nakada) 25 Jan '26

25 Jan '26

Issue #21787 has been reported by nobu (Nobuyoshi Nakada). ---------------------------------------- Bug #21787: `IO::Buffer` buffer overf https://bugs.ruby-lang.org/issues/21787 * Author: nobu (Nobuyoshi Nakada) * Status: Open * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- -- https://bugs.ruby-lang.org/

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[ruby-core:123795] [Ruby Bug#21685] Unnecessary context-switching, especially bad on multi-core machines.
by jpl-coconut (Jacob Lacouture) 22 Jan '26

22 Jan '26

Issue #21685 has been reported by jpl-coconut (Jacob Lacouture). ---------------------------------------- Bug #21685: Unnecessary context-switching, especially bad on multi-core machines. https://bugs.ruby-lang.org/issues/21685 * Author: jpl-coconut (Jacob Lacouture) * Status: Open * ruby -v: ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [aarch64-linux] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- While debugging a performance issue in a large rails application, I wrote a minimal microbenchmark that reproduces the issue. [[here]](https://gist.github.com/jpl-coconut/cb3679ce885eb578e1071c4b3a525d5c) I was surprised to see that the benchmark takes ~3.6sec on a single-core machine, and ~36sec **(10x slower) on a machine with 2 or more cores** . Initially I thought this was a bug in the implementation of Thread::Queue, but soon realized it relates to how the ruby reschedules threads around system calls. I prepared a fix in [[this branch]](https://github.com/jpl-coconut/ruby/tree/deferred_thread_wait) which is based off ruby 3.4.7. I can apply the fix to a different branch or to master if that's helpful. The fix simply defers suspending the thread until the syscall has been running for some short interval. I chose 100usec initially, but this could easily be made configurable. I pasted raw benchmark results below from a single run (though I did many runs and the results are stable). My CPU is an Apple M4. After the fix: - Single-core performance improves by 55%, from 3.6sec to 2sec. - Adding cores causes performance to be flat (at 2sec), rather than getting 10x slower. - Multi-core context-switch count reduces by 99.995%, from 1.4 million to ~80 - system_time/user_time ratio drops from (1.2 - 1.6) to 0.65 Here are the benchmark results before my change: ``` # time taskset --cpu-list 1 ./ruby qtest_simple.rb voluntary_ctxt_switches: 1140773 nonvoluntary_ctxt_switches: 9487 real 0m3.619s user 0m1.653s sys 0m1.950s # time taskset --cpu-list 1,2 ./ruby qtest_simple.rb voluntary_ctxt_switches: 1400110 nonvoluntary_ctxt_switches: 3 real 0m36.223s user 0m9.380s sys 0m14.927s ``` And after: ``` # time taskset --cpu-list 1 ./ruby qtest_simple.rb voluntary_ctxt_switches: 88 nonvoluntary_ctxt_switches: 899 real 0m2.031s user 0m1.209s sys 0m0.743s # time taskset --cpu-list 1,2 ./ruby qtest_simple.rb voluntary_ctxt_switches: 75 nonvoluntary_ctxt_switches: 8 real 0m2.062s user 0m1.279s sys 0m0.783s ``` I was concerned these results might still be reflective of a bug in Thread::Queue, so I also came up with a repro that doesn't rely on it. That one is [[here]](https://gist.github.com/jpl-coconut/aa14e59354abf98f808daaf39baa9a72). Results summary: - Single-core performance improves (this time by only 30%) - Multi-core penalty drops from 4x to 0. - No change to context-switching rates. - system_time/user_time ratio drops from (0.5-1) to 0.15 Before fix: ``` # time taskset --cpu-list 1 ./ruby mbenchmark.rb voluntary_ctxt_switches: 60 real 0m0.336s user 0m0.211s sys 0m0.118s # time taskset --cpu-list 1,2 ./ruby mbenchmark.rb voluntary_ctxt_switches: 60 real 0m1.424s user 0m0.468s sys 0m0.496s ``` After fix: ``` # time taskset --cpu-list 1 ./ruby mbenchmark.rb voluntary_ctxt_switches: 59 real 0m0.241s user 0m0.202s sys 0m0.032s # time taskset --cpu-list 1,2 ./ruby mbenchmark.rb voluntary_ctxt_switches: 60 real 0m0.238s user 0m0.195s sys 0m0.035s ``` -- 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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[ruby-core:123414] [Ruby Bug#21629] Ruby-3.4.7 fails to build using clang / llvm
by debo (David Bohman) 22 Jan '26

22 Jan '26

Issue #21629 has been reported by debo (David Bohman). ---------------------------------------- Bug #21629: Ruby-3.4.7 fails to build using clang / llvm https://bugs.ruby-lang.org/issues/21629 * Author: debo (David Bohman) * Status: Open * ruby -v: ruby 3.4.6 (2025-09-16 revision dbd83256b1) +PRISM [x86_64-darwin16] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- Here is the error I encountered. This is using clang version 21.1.3 as the compiler toolchain on Darwin. ``` DYLD_LIBRARY_PATH=.:../../.. ASAN_OPTIONS=detect_leaks=0 "clang -I../../../.ext/include/x86_64-darwin16 -I../../../../ruby-3.4.7/include -I../../../../ruby-3.4.7/ext/-test-/public_header_warnings -I/usr/local/include -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -D_DARWIN_UNLIMITED_SELECT -D_REENTRANT -fstack-protector-strong -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fdeclspec -O3 -fno-fast-math -ggdb3 -Wall -Wextra -Wextra-tokens -Wdeprecated-declarations -Wdivision-by-zero -Wdiv-by-zero -Wimplicit-function-declaration -Wimplicit-int -Wpointer-arith -Wshorten-64-to-32 -Wwrite-strings -Wold-style-definition -Wmissing-noreturn -Wno-cast-function-type -Wno-constant-logical-operand -Wno-long-long -Wno-missing-field-initializers -Wno-overlength-strings -Wno-parentheses-equality -Wno-self-assign -Wno-tautological-compare -Wno-unused-parameter -Wno-unused-value -Wunused-variable -Wmisleading-indentation -Wundef -fno-common -pipe -D_TEST_OK -Werror -c conftest.c" In file included from conftest.c:1: In file included from ../../../../ruby-3.4.7/include/ruby.h:38: In file included from ../../../../ruby-3.4.7/include/ruby/ruby.h:28: In file included from ../../../../ruby-3.4.7/include/ruby/internal/arithmetic.h:24: In file included from ../../../../ruby-3.4.7/include/ruby/internal/arithmetic/char.h:29: ../../../../ruby-3.4.7/include/ruby/internal/core/rstring.h:398:24: error: default initialization of an object of type 'struct RString' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe] 398 | struct RString retval; | ^ ../../../../ruby-3.4.7/include/ruby/internal/core/rbasic.h:86:17: note: member 'klass' declared 'const' here 86 | const VALUE klass; | ^ 1 error generated. checked program was: /* begin */ 1: #include "ruby.h" 2: 3: int main(int argc, char **argv) 4: { 5: return !!argv[argc]; 6: } /* end */ ``` The configuration is the following: ``` CC=clang CXX=clang++ CPPFLAGS=-I/usr/local/include LDFLAGS=-L/usr/local/lib ../ruby-3.4.7/configure --enable-shared --with-rdoc=ri,html ``` -- https://bugs.ruby-lang.org/

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[ruby-core:123923] [Ruby Bug#21716] YJIT panic: "all PendingBranchRefs should be unique" in net/http response reading (infinite unwind loop)
by angelim＠angelim.com.br (Alexandre Angelim) 22 Jan '26

22 Jan '26

Issue #21716 has been reported by angelim(a)angelim.com.br (Alexandre Angelim). ---------------------------------------- Bug #21716: YJIT panic: "all PendingBranchRefs should be unique" in net/http response reading (infinite unwind loop) https://bugs.ruby-lang.org/issues/21716 * Author: angelim(a)angelim.com.br (Alexandre Angelim) * Status: Open * ruby -v: ruby 3.4.7 * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- We encountered a YJIT panic in production that caused the process to enter an infinite logging loop for several hours. The panic occurs within `yjit/src/core.rs` when handling branch references. The trigger appears to be in `net/http`, specifically when reading a response body (possibly involving chunked encoding or zlib) inside a Datadog trace transport flush. Key Observations: The Panic: YJIT fails with all PendingBranchRefs should be unique when ready to construct a Block. The Loop: After the panic, the process fails to exit and instead logs `rust_begin_unwind` and `try_fold` iterator errors repeatedly, filling logs for hours. System Configuration Ruby Version: ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +YJIT +PRISM [aarch64-linux] Environment: Linux aarch64 (AWS Graviton/ARM) Reproduction Context While we cannot provide a standalone reproduction script yet, the crash happens intermittently during a Net::HTTP request initiated by datadog-ruby (v2.17.0) to flush traces to a Unix socket, which is wrapped by sentry-ruby (v5.26.0). Ruby Location: `/gems/net-http-0.6.0/lib/net/http/response.rb:604` Rust Location: `./yjit/src/core.rs:2403:27` Backtrace & Logs ``` ruby: YJIT has panicked. More info to follow... thread '<unnamed>' panicked at 'all PendingBranchRefs should be unique when ready to construct a Block', ./yjit/src/core.rs:2403:27 stack backtrace: 0: rust_begin_unwind at /rustc/.../library/std/src/panicking.rs:578:5 ... 28: yjit::core::branch_stub_hit at /workspace/ruby-3.4.7/yjit/src/core.rs:3492:9 /gems/net-http-0.6.0/lib/net/http/response.rb:604: [BUG] YJIT: panicked at 'all PendingBranchRefs should be unique when ready to construct a Block', ./yjit/src/core.rs:2403:27 -- Control frame information ----------------------------------------------- c:0047 p:0049 s:0248 e:000247 BLOCK /gems/net-http-0.6.0/lib/net/http/response.rb:604 c:0046 p:0098 s:0243 e:000242 METHOD /gems/net-http-0.6.0/lib/net/http/response.rb:588 c:0045 p:0004 s:0235 e:000234 METHOD /gems/net-http-0.6.0/lib/net/http/response.rb:593 ... c:0039 p:0033 s:0196 e:000195 BLOCK /gems/sentry-ruby-5.26.0/lib/sentry/net/http.rb:44 ... c:0033 p:0023 s:0158 e:000157 METHOD /gems/datadog-2.17.0/lib/datadog/core/transport/http/adapters/unix_socket.rb:43 c:0032 p:0066 s:0152 e:000151 METHOD /gems/datadog-2.17.0/lib/datadog/core/transport/http/adapters/net.rb:77 ``` The stack suggests the crash happens during `branch_stub_hit` resolution. The presence of sentry-ruby and datadog suggests complex interaction with Net::HTTP patching. The infinite loop of logs following the crash looks like this (repeated): ``` /usr/lib/libruby.so.3.4(try_fold<alloc::vec::into_iter::IntoIter<alloc::rc::Rc<yjit::core::PendingBranch> ... `` This suggests the panic handler itself is tripping over the corrupted `PendingBranch` state. We encountered a YJIT panic in production that caused the process to enter an infinite logging loop for several hours. The panic occurs within `yjit/src/core.rs` when handling branch references. The trigger appears to be in `net/http`, specifically when reading a response body (possibly involving chunked encoding or zlib) inside a Datadog trace transport flush. -- https://bugs.ruby-lang.org/

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[ruby-core:124408] [Ruby Bug#21816] iseq code_location miss calculated indent
by zzak (zzak _) 16 Jan '26

16 Jan '26

Issue #21816 has been reported by zzak (zzak _). ---------------------------------------- Bug #21816: iseq code_location miss calculated indent https://bugs.ruby-lang.org/issues/21816 * Author: zzak (zzak _) * Status: Open * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- TBH, I'm not really sure if that title matches the problem here, but I can produce this issue with the following test: ```ruby # bug.rb # note the indentation of the callable callable = -> { puts "Hello, World!" } iseq = RubyVM::InstructionSequence.of(callable) pp iseq.to_a pp iseq.to_a[4] pp iseq.to_a[4][:code_location][1] ``` Ruby 4.0.0: ``` $ ruby -v bug.rb ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [x86_64-linux] ["YARVInstructionSequence/SimpleDataFormat", 4, 0, 1, {arg_size: 0, local_size: 0, stack_max: 2, node_id: 7, code_location: [1, 15, 1, 40], node_ids: [4, 5, 4, 7], parser: :prism}, "block in <main>", "bug.rb", "/tmp/tmp.Fbq5WA0GnO/bug.rb", 1, :block, [], {}, [], [1, :RUBY_EVENT_LINE, :RUBY_EVENT_B_CALL, [:putself], [:putchilledstring, "Hello, World!"], [:opt_send_without_block, {mid: :puts, flag: 20, orig_argc: 1}], :RUBY_EVENT_B_RETURN, [:leave]]] {arg_size: 0, local_size: 0, stack_max: 2, node_id: 7, code_location: [1, 15, 1, 40], node_ids: [4, 5, 4, 7], parser: :prism} 15 ``` Ruby 4.1.0: ``` $ ruby -v bug.rb ruby 4.1.0dev (2025-12-30T18:02:00Z master 9d37155cfc) +PRISM [x86_64-linux] ["YARVInstructionSequence/SimpleDataFormat", 4, 1, 1, {arg_size: 0, local_size: 0, stack_max: 2, node_id: 7, code_location: [1, 13, 1, 40], node_ids: [4, 5, 4, 7], parser: :prism}, "block in <main>", "bug.rb", "/tmp/tmp.Fbq5WA0GnO/bug.rb", 1, :block, [], {}, [], [1, :RUBY_EVENT_LINE, :RUBY_EVENT_B_CALL, [:putself], [:putchilledstring, "Hello, World!"], [:opt_send_without_block, {mid: :puts, flag: 20, orig_argc: 1}], :RUBY_EVENT_B_RETURN, [:leave]]] {arg_size: 0, local_size: 0, stack_max: 2, node_id: 7, code_location: [1, 13, 1, 40], node_ids: [4, 5, 4, 7], parser: :prism} 13 ``` For context: This second value being 13 instead of 15 is causing Rails tests to fail: https://buildkite.com/rails/rails-nightly/builds/3447#019b710f-e78a-405f-82… We want: ``` { @object.num } ``` But we get: ``` -> { @object.num } ``` I am pretty sure using the same version of `prism`: ``` /tmp/tmp.Fbq5WA0GnO => rbenv shell 4.1.0 /tmp/tmp.Fbq5WA0GnO => gem list | grep prism prism (1.7.0) /tmp/tmp.Fbq5WA0GnO => rbenv shell 4.0.0 /tmp/tmp.Fbq5WA0GnO => gem list | grep prism prism (1.7.0) ``` We use this data to get the original source string of a block we use to decorate the `assert_difference` assertion: https://github.com/rails/rails/blob/3d31d593e6cf0f82fa9bd0338b635af2f30d627… https://api.rubyonrails.org/classes/ActiveSupport/Testing/Assertions.html#m… -- https://bugs.ruby-lang.org/

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[ruby-core:124054] [Ruby Misc#21768] Remove deprecated functions
by nobu (Nobuyoshi Nakada) 16 Jan '26

16 Jan '26

Issue #21768 has been reported by nobu (Nobuyoshi Nakada). ---------------------------------------- Misc #21768: Remove deprecated functions https://bugs.ruby-lang.org/issues/21768 * Author: nobu (Nobuyoshi Nakada) * Status: Open ---------------------------------------- -- https://bugs.ruby-lang.org/

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[ruby-core:124047] [Ruby Feature#21766] Pathname + FileUtils making sweet music together
by gurgeous (Adam Doppelt) 16 Jan '26

16 Jan '26

Issue #21766 has been reported by gurgeous (Adam Doppelt). ---------------------------------------- Feature #21766: Pathname + FileUtils making sweet music together https://bugs.ruby-lang.org/issues/21766 * Author: gurgeous (Adam Doppelt) * Status: Open ---------------------------------------- I love Pathname. I love FileUtils. Let's bring these two classes EVEN CLOSER TOGETHER by adding some tragically missing helpers. Something like this, perhaps? ``` ruby class Pathname def mkdir_p(...) = FileUtils.mkdir_p(@path, ...) def ln(...) = FileUtils.ln(@path, ...) def ln_s(...) = FileUtils.ln_s(@path, ...) def ln_sf(...) = FileUtils.ln_sf(@path, ...) def cp(...) = FileUtils.cp(@path, ...) def cp_r(...) = FileUtils.cp_r(@path, ...) def mv(...) = FileUtils.mv(@path, ...) def rm(...) = FileUtils.rm(@path, ...) def rm_r(...) = FileUtils.rm_r(@path, ...) def rm_rf(...) = FileUtils.rm_rf(@path, ...) end ``` There are some concerns about making pathname.rb more dependent on FileUtils, which I understand. What's the best way forward? Let's do it! (also see https://github.com/ruby/pathname/issues/64 and https://github.com/ruby/pathname/issues/72) -- https://bugs.ruby-lang.org/

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[ruby-core:124288] [Ruby Bug#21790] `Socket.getaddrinfo` hangs after `fork()` on macOS 26.1 (Tahoe) for IPv4-only hosts
by adamoffat (Adam Moffat) 13 Jan '26

13 Jan '26

Issue #21790 has been reported by adamoffat (Adam Moffat). ---------------------------------------- Bug #21790: `Socket.getaddrinfo` hangs after `fork()` on macOS 26.1 (Tahoe) for IPv4-only hosts https://bugs.ruby-lang.org/issues/21790 * Author: adamoffat (Adam Moffat) * Status: Open * ruby -v: 3.3.8 * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- Ruby's `Socket.getaddrinfo` hangs indefinitely in forked child processes on macOS 26.1 (Tahoe) when resolving IPv4-only hostnames. This is a regression that does not occur on macOS 15.x (Sonoma) or earlier. **Ruby version:** ruby 3.3.8 (2025-04-09 revision b200bad6cd) [arm64-darwin24] Also confirmed this affects Ruby 3.2.6 and 3.4.1. **Reproducible script:** ``` ruby require "socket" require "timeout" puts "Ruby #{RUBY_VERSION} on #{RUBY_PLATFORM}" Socket.getaddrinfo("api.segment.io", 443, nil, :STREAM) puts "Parent: DNS completed" pid = fork do puts "Child: Attempting DNS resolution..." begin Timeout.timeout(90) do Socket.getaddrinfo("api.segment.io", 443, nil, :STREAM) end puts "Child: SUCCESS" exit 0 rescue Timeout::Error puts "Child: FAILED - hung for 90 seconds" exit 1 end end Process.wait(pid) ``` **Note:** Remove the `Timeout.timeout(90)` wrapper to observe the hang indefinitely. The timeout is included only to allow the script to exit for testing purposes. **Result of reproduce process:** ``` Ruby 3.3.8 on arm64-darwin24 Parent: DNS completed Child: Attempting DNS resolution... Child: FAILED - hung for 90 seconds ``` The child process hangs with one thread consuming 100% CPU. Expected result: The child process should complete DNS resolution successfully, as it does on macOS 15.x and earlier. **Analysis:** Stack trace shows: Main thread: Blocked in `wait_getaddrinfo` → `_pthread_cond_wait` DNS thread: Spinning in `_gai_nat64_second_pass` → `nw_path_access_agent_cache` → `_os_log_preferences_refresh` → `SIGSEGV` The crash occurs in macOS's NAT64 synthesis code path. Ruby's signal handler catches the `SIGSEGV` but cannot recover, causing the DNS thread to spin. **Key observations:** - Only affects IPv4-only hosts. Hosts with IPv6 (like google.com) work correctly. - Using `AF_INET` instead of `AF_UNSPEC` works. `Socket.getaddrinfo("api.segment.io", 443, Socket::AF_INET, :STREAM)` succeeds. - Python is not affected. Python calls `getaddrinfo()` synchronously without a background thread. - Parent must do DNS before fork. If the parent has not called getaddrinfo(), the child works correctly. **Workaround:** - Use `resolv-replace` to bypass the native DNS resolver: `require "resolv-replace"` **Impact:** This breaks all Ruby applications using pre-forking worker models (Resque, Unicorn, Puma, Sidekiq, Passenger) on macOS Tahoe. **Apple Bug Report:** Filed with Apple as Feedback Assistant #FB21364061 ---Files-------------------------------- stack_trace.txt (66.6 KB) ruby_dns_fork_bug.rb (1.02 KB) -- https://bugs.ruby-lang.org/

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