- ruby-core - ml.ruby-lang.org

[ruby-core:125122] [Ruby Feature#8948] Frozen regex
by Eregon (Benoit Daloze) 24 Mar '26

24 Mar '26

Issue #8948 has been updated by Eregon (Benoit Daloze). From the discussion at the dev meeting https://github.com/ruby/dev-meeting-log/blob/master/2026/DevMeeting-2026-01… > matz: try freezing Regexp instances, but no subclasses, and revisit it to check compatibility issues. I will adjust the PR (https://github.com/ruby/ruby/pull/14547) to do that. ---------------------------------------- Feature #8948: Frozen regex https://bugs.ruby-lang.org/issues/8948#change-116842 * Author: sawa (Tsuyoshi Sawada) * Status: Assigned * Assignee: Eregon (Benoit Daloze) * Target version: 4.1 ---------------------------------------- =begin I see that frozen string was accepted for Ruby 2.1, and frozen array and hash are proposed in https://bugs.ruby-lang.org/issues/8909. I feel there is even more use case for a frozen regex, i.e., a regex literal that generates a regex only once. It is frequent to have a regex within a frequently repeated portion of code, and generating the same regex each time is a waste of resource. At the moment, we can have a code like: class Foo RE1 = /pattern1/ RE2 = /pattern1/ RE3 = /pattern1/ def classify case self when RE1 then 1 when RE2 then 2 when RE3 then 3 else 4 end end end but suppose we have a frozen `Regexp` literal `//f`. Then we can write like: class Foo def classify case self when /pattern1/f then 1 when /pattern1/f then 2 when /pattern1/f then 3 else 4 end end end =end -- https://bugs.ruby-lang.org/

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[ruby-core:124414] [Ruby Bug#21818] Thread backtraces cannot be communicated over Ractor ports
by dazuma (Daniel Azuma) 24 Mar '26

24 Mar '26

Issue #21818 has been reported by dazuma (Daniel Azuma). ---------------------------------------- Bug #21818: Thread backtraces cannot be communicated over Ractor ports https://bugs.ruby-lang.org/issues/21818 * Author: dazuma (Daniel Azuma) * Status: Open * ruby -v: ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [arm64-darwin25] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- It looks like Thread::Backtrace is confined to the Ractor that produced it: it cannot be copied or moved to another Ractor, nor can it be made shareable. This makes it difficult for a Ractor to communicate exceptions (e.g. the reason for its own failure) to other Ractors. Is this intentional? I would have expected that a Thread::Backtrace is just static data that should not have problems moving between Ractors. Details below: **Thread::Backtrace cannot be moved to another Ractor** Code: ``` def make_trace caller_locations end r1 = Ractor.new do port = receive trace = make_trace puts "**** Original: #{trace.inspect}" port.send(trace, move: true) # Fails here end port = Ractor::Port.new r1.send(port) trace = port.receive # Hangs here puts "**** Received: #{trace.inspect}" ``` Result: ``` **** Original: ["hello.rb:7:in 'block in <main>'"] #<Thread:0x000000010438f770 run> terminated with exception (report_on_exception is true): hello.rb:9:in 'Ractor::Port#send': can not move Thread::Backtrace::Location object. (Ractor::Error) from hello.rb:9:in 'block in <main>' ``` As a result, it is also not possible to move an Exception: ``` r1 = Ractor.new do port = receive begin raise "hello" rescue => e port.send(e, move: true) # Fails here end end port = Ractor::Port.new r1.send(port) e = port.receive # Hangs here ``` Result: ``` #<Thread:0x0000000102a0f570 run> terminated with exception (report_on_exception is true): hello.rb:6:in 'Ractor::Port#send': can not move Thread::Backtrace object. (Ractor::Error) from hello.rb:6:in 'block in <main>' ``` Note that Kernel#caller returns a string array that can be moved successfully: ``` def make_trace caller end r1 = Ractor.new do port = receive trace = make_trace puts "**** Original: #{trace.inspect}" port.send(trace, move: true) end port = Ractor::Port.new r1.send(port) trace = port.receive puts "**** Received: #{trace.inspect}" ``` Result: ``` **** Original: ["hello.rb:7:in 'block in <main>'"] **** Received: ["hello.rb:7:in 'block in <main>'"] ``` **Thread::Backtrace cannot be *copied* to another Ractor either** Code: ``` def make_trace caller_locations end r1 = Ractor.new do port = receive trace = make_trace puts "**** Original: #{trace.inspect}" port.send(trace, move: false) # Fails here end port = Ractor::Port.new r1.send(port) trace = port.receive # Hangs here puts "**** Received: #{trace.inspect}" ``` Result. Note the specific error message "allocator undefined" that might give a clue why this is all happening: ``` **** Original: ["hello.rb:7:in 'block in <main>'"] #<Thread:0x000000010031f5c8 run> terminated with exception (report_on_exception is true): hello.rb:9:in 'Ractor::Port#send': allocator undefined for Thread::Backtrace::Location (TypeError) port.send(trace, move: false) ^^^^^^^^^^^^^^^^^^ from hello.rb:9:in 'block in <main>' ``` Again, Kernel#caller returns a string array that copies successfully: ``` def make_trace caller end r1 = Ractor.new do port = receive trace = make_trace puts "**** Original: #{trace.inspect}" port.send(trace, move: false) # Fails here end port = Ractor::Port.new r1.send(port) trace = port.receive # Hangs here puts "**** Received: #{trace.inspect}" ``` Result: ``` **** Original: ["hello.rb:7:in 'block in <main>'"] **** Received: ["hello.rb:7:in 'block in <main>'"] ``` Interestingly, if an exception is copied when sent over a port, it doesn't fail with an undefined allocator, but the backtrace in the copy is empty: ``` r1 = Ractor.new do port = receive begin raise "hello" rescue => e puts "**** Original: #{e.backtrace.inspect}" port.send(e, move: false) end end port = Ractor::Port.new r1.send(port) e = port.receive puts "**** Received: #{e.backtrace.inspect}" ``` Result: ``` **** Original: ["hello.rb:4:in 'block in <main>'"] **** Received: [] ``` **Thread::Backtrace cannot be made shareable** Code: ``` def make_trace caller_locations end trace = Ractor.make_shareable(make_trace) # Fails here ``` Result: ``` hello.rb:5:in 'Ractor.make_shareable': can not make shareable object for "hello.rb:5:in '<main>'" (Ractor::Error) from hello.rb:5:in '<main>' ``` As a result, exceptions also cannot be made shareable: ``` begin raise "hello" rescue => e e = Ractor.make_shareable(e) # Fails here end ``` Result: ``` hello.rb: can not make shareable object for #<Thread::Backtrace:0x0000000102fdfe28> (Ractor::Error) ``` Interestingly, if the backtrace is empty, make_shareable succeeds, suggesting that it's specifically the Thread::Backtrace::Location that cannot be made shareable: ``` trace = Ractor.make_shareable(caller_locations) puts trace.inspect ``` Result: ``` [] ``` And, of course, the result of Kernel#caller can be made shareable: ``` def make_trace caller end trace = Ractor.make_shareable(make_trace) puts trace.inspect ``` Result: ``` ["hello.rb:5:in '<main>'"] ``` -- https://bugs.ruby-lang.org/

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[ruby-core:123672] [Ruby Feature#21665] Revisit Object#deep_freeze to support non-Ractor use cases
by headius (Charles Nutter) 24 Mar '26

24 Mar '26

Issue #21665 has been reported by headius (Charles Nutter). ---------------------------------------- Feature #21665: Revisit Object#deep_freeze to support non-Ractor use cases https://bugs.ruby-lang.org/issues/21665 * Author: headius (Charles Nutter) * Status: Open ---------------------------------------- ## Proposal: Introduce `Object#deep_freeze` (or similar name) to freeze an entire object graph I would like to re-propose the addition of Object#deep_freeze as a way to explicitly freeze an entire object graph. This proposal was rejected some years ago after being brought up in https://bugs.ruby-lang.org/issues/17145. The proposal was rejected in favor of making Ractor-specific methods like Ractor.make_shareable. There are a number of reasons why I believe `deep_freeze` is still an important addition: * Rubyists have been requesting a way to deep freeze an object graph for many years (decades?), far longer than Ractor has existed. * Immutable objects are the safest way to safe concurrency, with or without parallel threading or Ractor. * In fact, deep freezing has utility *completely unrelated to concurrency*, such as to guarantee that a large graph of objects will not be modified in the future. * In the absence of `deep_freeze`, users have been forced to implement the behavior themselves, rely on third-party libraries, or call `Ractor.make_shareable` even if they never intend to use Ractor. * The existing `Ractor.make_shareable` primarily does a deep freeze internally. Given the steady move toward making immutability the norm in Ruby, it seems clear to me that deep freezing is a feature that is long overdue. ## Revisiting arguments for rejecting `deep_freeze`: A number of reasons were given in #17145 for preferring the `Ractor.make_shareable` method and rejecting `deep_freeze`. I address those here: @ko1: > One concern about the name "freeze" is, what happens on shareable objects on Ractors. > For example, Ractor objects are shareable and they don't need to freeze to send beyond Ractor boundary. As mentioned above, deep freezing has utility completely separate from Ractors and concurrency. It is a frequently-requested and very useful feature to add. I think we should treat this as a standalone feature, and treat enhancements for Ractors as a separate concern. @ko1: > I also want to introduce Mutable but shareable objects using STM (or something similar) writing protocol (shareable Hash). What happens on deep_freeze? Five years later, I believe this has not yet happened. A potential future optimization for Ractor should not be justification to reject a useful feature today. If users implement their code using primarily immutable objects now, it's unlikely that they will want those same objects to be mutable in the future (this applies to deep freezing as well as `make_shareable`). @eregon: > A dynamic call to freeze causes extra calls, and needs checks that it was indeed frozen. > So for efficiency I think it would be better to mark as frozen internally without a call to freeze on every value. I agree with the concerns about dynamic calls to freeze and overridden versions of the method. It may make more sense to implement this as a utility method, like `Object.deep_freeze(obj)` (a non-overridable class utility method). This is essentially what has been implemented within `Ractor.make_shareable` today. @ko1: > Maybe the author don't want to care about Ractor. > The author want to declare "I don't touch it". So "deep_freeze" is better. This was actually given as a justification for a `deep_freeze` method versus something like `Object#to_shareable`, and yet what we ended up with was a method that requires users know about Ractor. I believe there should be a `deep_freeze` method that has nothing to do with Ractor. And users on JRuby and TruffleRuby already can get full parallelism today without Ractor. They do not care about Ractor, but they definitely care about deep freezing. @eregon: > I don't like anything with "ractor" in the name, that becomes not descriptive of what it does and IMHO looks weird for e.g. gems not specifically caring about Ractor. This is a large part of my justification for revisiting this proposal. Users should not have to care about or want to use Ractor just so they can deep freeze an object graph, because it has utility far beyond Ractor. @ko1: > I implemented Object#deep_freeze(skip_shareable: false) for trial. > https://github.com/ko1/ruby/pull/new/deep_freeze There's already a prototype of this, though I suspect this logic essentially became `Ractor.make_shareable` in the end. I believe it would be acceptable to implement `Ractor.make_shareable` by calling `deep_freeze` since there's largely no difference in visible behavior (other than Ractor-specific optimizations like marking a whole graph as shareable). @eregon: > How about first having deep_freeze that just freezes everything (except an object's class)? This is a good proposal. I believe it is what 99% of users currently calling `make_shareable` actually want, and again there's utility well beyond Ractor and concurrency scenarios. @eregon: > So we could mark as deeply frozen first, and remember to undo that if we cannot freeze some object. > However, is there any object that cannot be frozen? I would think not. The majority of uses of `make_shareable` I have seen are called exactly once on a graph of objects. It does not seem to be typical to repeatedly call `make_shareable`. I understand the desire to have a `shareable` bit for Ractor optimization, but that is a *separate feature* from deep freezing an object graph. There are many cases where we will only call `deep_freeze` once to ensure a graph is fully frozen before publishing it for other code to see, and most of these cases will not try to re-deep-freeze that graph. Ractor's need to "double-check" shareability is orthogonal to the discussion about deep freezing and should not be justification for rejecting `deep_freeze`. @eregon brought up concerns about not calling the custom `freeze` method on user types, since they may want to eagerly cache some data. I believe that discussion is out of scope. `deep_freeze` would be defined to only free the objects that are directly walkable from a root object, and only setting frozen bits. A new overridable method could be introduced that `deep_freeze` would call if present, but otherwise it should just do fast-path object freeze flag setting. @marcandre: > Looking at def freeze in the top ~400 gems, I found 64 in sequel gem alone, and 28 definitions in the rest 😅. This comment provides a breakdown of custom `freeze` methods and the reasons they are implemented. Again, I believe this is out of scope for the discussion at hand. Forcing objects to "prepare for deep freezing" is a separate consideration that will be very library-specific, since every library may want to prepare in a different way. But they *all* want the ability to recursively mark objects as frozen, which is a runtime-level feature. @ko1: > We discussed about the name "deep_freeze", and Matz said deep_freeze should be only for freezing, not related to Ractor. So classes/module should be frozen if [C].deep_freeze. This is why I proposed a Object#deep_freeze(skip_shareable: true) and Ractor.make_shareable(obj). Avoiding classes and modules when deep freezing seems like a reasonable option to me. Naming could make this behavior clear, but again I believe 99% of users just want a plain old object `deep_freeze`. And this is again conflating two separate concerns: * deep freezing * marking an entire graph as shareable These are – and should be – two separate features. The deep freezing feature should not depend on setting shareability bits, since shareability is only meaningful in the context of Ractors. @ko1: > So naming issue is reamained? > > Object#deep_freeze (matz doesn't like it) > Object#deep_freeze(skip_sharable: true) (I don't know how Matz feel. And it is difficult to define Class/Module/... on skip_sharable: false) > Ractor.make_shareable(obj) (clear for me, but it is a bit long) > Ractor.shareable!(obj) (shorter. is it clear?) > Object#shareable! (is it acceptable?) > ... other ideas? I outline some alternatives below. ## Alternative forms: @matz didn't like `deep_freeze` five years ago. How do you feel about it now, @matz? Some alternatives with justification: * Object.deep_freeze(obj) This would make sense to avoid users being able to override the `deep_freeze` behavior, and would make it feel more like a global utility method with special behavior. * Object#freeze(obj, deep: true) * Object#freeze(obj, recursive: true) These work within the existing `freeze` method and still convey intent, but may break APIs that don't expect to receive keyword arguments. And there are some alternative names, which may work as either instance methods or class methods: * `freeze_recursive` * `freeze_all` * `freeze!` * `freeze_reachable_objects` (long but a variation of this might address concerns about not freezing classes and modules) -- https://bugs.ruby-lang.org/

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[ruby-core:124417] [Ruby Bug#21819] A Data object should be frozen even if it has no members
by dazuma (Daniel Azuma) 24 Mar '26

24 Mar '26

Issue #21819 has been reported by dazuma (Daniel Azuma). ---------------------------------------- Bug #21819: A Data object should be frozen even if it has no members https://bugs.ruby-lang.org/issues/21819 * Author: dazuma (Daniel Azuma) * Status: Open * ruby -v: ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [arm64-darwin25] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- Data objects with at least one member are currently automatically frozen on construction, and shareable if all members are shareable. However, a Data object with no members is not frozen on construction. I would expect such an object similarly to be frozen (and also shareable since it has no non-shareable members). ``` Foo = Data.define(:foo) Foo.new(1).frozen? # => true Bar = Data.define Bar.new.frozen? # => false ``` -- https://bugs.ruby-lang.org/

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[ruby-core:124388] [Ruby Bug#21814] 0.pow(2,-9999999999999999990) should be zero
by matz (Yukihiro Matsumoto) 24 Mar '26

24 Mar '26

Issue #21814 has been reported by matz (Yukihiro Matsumoto). ---------------------------------------- Bug #21814: 0.pow(2,-9999999999999999990) should be zero https://bugs.ruby-lang.org/issues/21814 * Author: matz (Yukihiro Matsumoto) * Status: Open * Target version: 4.0 * ruby -v: 4.1dev * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- When I try `0.pow(2,-9999999999999999990)`, irb prints `-9999999999999999990`, but I think no matter what you divide zero by, the modulo should be zero. Matz. -- https://bugs.ruby-lang.org/

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[ruby-core:124381] [Ruby Bug#21811] Backport GH-15763
by nobu (Nobuyoshi Nakada) 24 Mar '26

24 Mar '26

Issue #21811 has been reported by nobu (Nobuyoshi Nakada). ---------------------------------------- Bug #21811: Backport GH-15763 https://bugs.ruby-lang.org/issues/21811 * Author: nobu (Nobuyoshi Nakada) * Status: Closed * Backport: 3.2: REQUIRED, 3.3: REQUIRED, 3.4: REQUIRED, 4.0: REQUIRED ---------------------------------------- https://github.com/ruby/ruby/pull/15763 -- https://bugs.ruby-lang.org/

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[ruby-core:124187] [Ruby Bug#21779] Do not export functions from statically linked extensions
by nobu (Nobuyoshi Nakada) 24 Mar '26

24 Mar '26

Issue #21779 has been reported by nobu (Nobuyoshi Nakada). ---------------------------------------- Bug #21779: Do not export functions from statically linked extensions https://bugs.ruby-lang.org/issues/21779 * Author: nobu (Nobuyoshi Nakada) * Status: Open * Backport: 3.2: REQUIRED, 3.3: REQUIRED, 3.4: REQUIRED ---------------------------------------- Reported at https://github.com/ruby/io-console/pull/105. This is caused by `InitVM_console` exposed from the statically linked io/console is called from the loaded io-console gem. The static `InitVM_console` initializes the ractor local storage key, but it is different from the key used in the gem extension. Also, [the workaround for conflict between `Init` functions](commit:ae8990aef098410ecc2b5f48fea9d7d171a3c5f6) is necessary for `InitVM` functions too. -- https://bugs.ruby-lang.org/

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[ruby-core:122558] [Ruby Bug#21446] StackOverflow when changing visibility in reopened refinement
by luke-gru (Luke Gruber) 24 Mar '26

24 Mar '26

Issue #21446 has been reported by luke-gru (Luke Gruber). ---------------------------------------- Bug #21446: StackOverflow when changing visibility in reopened refinement https://bugs.ruby-lang.org/issues/21446 * Author: luke-gru (Luke Gruber) * Status: Open * ruby -v: 3.5.0 * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- ```ruby class A def a :a end end class B < A end module R refine B do private :a end end module R refine B do public :a end end using R B.new.a # StackOverflow ``` I would expect it to change the visibility, not to overflow the stack. -- https://bugs.ruby-lang.org/

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[ruby-core:121642] [Ruby Bug#21266] YJIT GC safety crash with proc objects as block argument
by alanwu (Alan Wu) 23 Mar '26

23 Mar '26

Issue #21266 has been reported by alanwu (Alan Wu). ---------------------------------------- Bug #21266: YJIT GC safety crash with proc objects as block argument https://bugs.ruby-lang.org/issues/21266 * Author: alanwu (Alan Wu) * Status: Open * Assignee: yjit * Backport: 3.2: DONTNEED, 3.3: REQUIRED, 3.4: REQUIRED ---------------------------------------- ```ruby # Run with --yjit-call-threshold=1 def foo(args) = bar(*args, &proc { _1 }) def bar(_, _, _, _, *rest) = yield rest GC.stress = true foo([1,2,3,4]) foo([1,2,3,4]) ``` The proc in these calls get collected on the yield to the GC to allocate the rest parameter arary. ``` ../vm_core.h:1668: Assertion Failed: vm_block_handler_type:rb_obj_is_proc(block_handler) ``` Or in release builds: ``` ../test.rb:1: [BUG] Segmentation fault at 0x0000000000000020 ruby 3.3.6 (2024-11-05 revision 75015d4c1f) +YJIT [arm64-darwin24] -- C level backtrace information ------------------------------------------- /Users/alan/.rubies/ruby-3.3.6/bin/ruby(rb_vm_bugreport+0xb4c) [0x104595590] /Users/alan/.rubies/ruby-3.3.6/bin/ruby(rb_bug_for_fatal_signal+0x100) [0x1043d6120] /Users/alan/.rubies/ruby-3.3.6/bin/ruby(sig_do_nothing+0x0) [0x1044fc4b0] /usr/lib/system/libsystem_platform.dylib(_sigtramp+0x38) [0x187572de4] /Users/alan/.rubies/ruby-3.3.6/bin/ruby(rb_vm_invokeblock+0x144) [0x10456b004] ``` -- https://bugs.ruby-lang.org/

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[ruby-core:124971] [Ruby Feature#21950] Add a built-in CPU-time profiler
by osyoyu (Daisuke Aritomo) 19 Mar '26

19 Mar '26

Issue #21950 has been reported by osyoyu (Daisuke Aritomo). ---------------------------------------- Feature #21950: Add a built-in CPU-time profiler https://bugs.ruby-lang.org/issues/21950 * Author: osyoyu (Daisuke Aritomo) * Status: Open ---------------------------------------- Modern CRuby workloads can consume CPU concurrently across multiple native threads, especially with multiple Ractors and C exts which release the GVL. I'd like to propose the idea of integrating a built-in CPU-time profiler CRuby to enable more accurate and stable profiling in such situations. ## Motivation & Background CPU profilers indicate how much CPU time were consumed by different methods. Most CPU-time profilers rely on the kernel to track consumed CPU time. `setitimer(3)` and `timer_create(3)` are APIs to configure kernel timers. The process receives a profiling signal (SIGPROF) every given time of CPU time consumed (e.g. 10 ms). In general, a profiler needs to know which _thread_ consumed how much CPU time to attribute work to the correct thread. This wasn't a real requirement for Ruby in the pre-Ractor age, since only one native thread could consume CPU time at any given moment due to GVL limitations. Using process-wide CPU-time timers provided by `setitimer()` effectively did the job. It was safe to assume that the active thread was doing some work using the CPU when a profiling signal arrived. Of course, this assumption does not stand in all situations. One is the case where C extensions release the GVL. Another is the multi-Ractor situation. In these cases, multiple native threads may simultaneously consume CPU time. Linux 2.6.12+ provides a per-thread timer to address this task. Profilers such as [Pf2](https://github.com/osyoyu/pf2) and [dd-trace-rb](https://github.com/DataDog/dd-trace-rb) use this feature to keep track of CPU time. However, utilizing this API requires information that CRuby does not necessarily expose. Both carry copies of CRuby headers in order to access internal structs such as `rb_thread_t`. This is quite fragile and possibly unsustainable in the age where CRuby evolves towards Ractors and M:N threading. ## Proposal Implement a built-in CPU-time profiler as `ext/profile`, and add some information extraction points to the VM built exclusively for it. ```ruby require 'profile' RubyVM::Profile.start # your code here RubyVM::Profile.stop #=> results ``` `ext/profile` will take care of the following in coordination with some VM helpers: - Tracking creation and destruction of native thread (NT) s - Management of kernel timers for those threads - i.e. calling `pthread_getcpuclockid(3)` and `timer_create(3)` - This will require iterating over all Ractors and shared NTs on profiler init - Handling of SIGPROF signals which those timers will generate - Walking the stack (calling `rb_profile_frames()`) - I'm not going to make this part of this ticket, but I'm thinking we can make `rb_profile_frames()` even more granular by following VM instructions, which is probably something we don't want to expose as an API We would need to add some APIs to the VM for `ext/profile`: - An API returning all alive NTs - Event hooks notifying creation and destruction of NTs - Event hooks notifying assign/unassign of RTs to NTs Since only Linux provides the full set of required kernel features, the initial implementation will be limited to Linux systems. I can expand support to other POSIX systems by employing `setitimer()` later, but they will receive limited granularity (process-level CPU-time timers). ### Output interface One thing to consider is the output format. I think we have a few practical choices here: - Adopt pprof's `profile.proto` format. - This is a widely accepted format across tools including visualizers. - The format itself is pretty flexible, so it shouldn't be hard to add custom fields. - Just return a Hash containing profile results. - We'd need to design some good format. ### Things out of scope - Visualization - Interaction with external visualizers / trackers / etc These can be better left to normal RubyGems. ### Why not an external gem? Through maintaining [Pf2](https://github.com/osyoyu/pf2), an CPU-time profiler library, I have encountered many difficulties obtaining information required for accurate profiling. The rule of thumb is that more internal information a profiler can access, the more accuracy it can achieve. However, from the CRuby maintenance perspective, I suppose not too many APIs exposing implementation details are wanted. Locating a profiler under `ext/` looks like nice middle ground. Placing core 'profiling' logic (sampler scheduling, sampling itself) in CRuby and abstracting it as 'RubyVM::Profile' should work cleanly. It should be noted that existing profilers have their own unique features, such as markers, unwinding of C stacks and integration with external APMs. I don't want to make this a tradeoff between accuracy and feature; instead, I'd like to design an API where both could live. ### Study on other languages A handful of VM-based languages carry profiler implementation in their runtime. - Go: runtime/pprof https://github.com/golang/go/tree/master/src/runtime/pprof - OpenJDK: JFR https://github.com/openjdk/jdk/tree/master/src/hotspot/share/jfr - Node.js: --cpu-prof https://nodejs.org/en/learn/getting-started/profiling - And more Among these, OpenJDK is a notable entry. JVM profilers have configured used `AsyncGetCallTrace()`, which is just like `rb_profile_frames()`, to obtain stack traces from signal handlers. The signal originates from kernel timers installed by the profilers, configured to fire every specified interval of CPU time (e.g. 10 ms). Even though `AsyncGetCallTrace()` and async-profiler (its primary user) are very sophisticated and battle-tested, JFR folks have decided to control sampling timing within the runtime to improve accuracy and stability. For more information on JVM, see: - [JEP 509](https://openjdk.org/jeps/509) - [JEP 518](https://openjdk.org/jeps/518) - [Taming the Bias: Unbiased* Safepoint-Based Stack Walking in JFR](https://mostlynerdless.de/blog/2025/05/20/taming-the-bias-unbiased-safepoint-based-stack-walking-in-jfr/) -- https://bugs.ruby-lang.org/

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