# JRuby disabling ObjectSpace: what implications? **URL:** \ **Category:** Ruby\ **Created:** [October 28, 2007, 7:54am UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533 "2007-10-28T07:54:19Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 7:54am UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/1 "2007-10-28T07:54:19Z")
As some of you may have heard, we’re considering disabling ObjectSpace.each\_object by default in JRuby. Primarily, this is for performance; to support each\_object, we have to bend over backwards, maintaining lists of weak references to all objects in the system and periodically cleaning out those lists. Here’s some example performance, from a fractal benchmark in the JRuby source: With ObjectSpace: Ruby Elapsed 45.967000 Without ObjectSpace: Ruby Elapsed 4.280000 What’s most frustrating about this is that almost _no_ libraries or apps use each\_object, and it’s a terrible performance hit for us. The one really visible use of each\_object is in test/unit, where the default console-based runner does each\_object(Class) to find all subclasses of TestCase. Because this is a heavily-used library (to say the least), I’ve made modifications to JRuby to always support each\_object(Class) by maintaining a bidirectional graph of parent and child classes. So that much wouldn’t go away (but I’d prefer an implementation that uses Class#inherited, since it would be cleaner, faster, and deterministic). So…I’m writing this to see what the general Ruby world thinks of us having ObjectSpace disabled by default, enableable via a command line option (or perhaps through a library? -robjectspace?). I think more and more of you may want to give JRuby another look over the next few months, so I think we need to involve you in such decisions. - Charlie ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 7:59am UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/2 "2007-10-28T07:59:35Z")
From: “Charles Oliver N.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > As some of you may have heard, we’re considering disabling > ObjectSpace.each\_object by default in JRuby. Primarily, this is for > performance; to support each\_object, we have to bend over backwards, > maintaining lists of weak references to all objects in the system and > periodically cleaning out those lists. Is this also true for ObjectSpace#\_id2ref ? Regards, Bill ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 8:17am UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/3 "2007-10-28T08:17:06Z")
Bill K. wrote: > From: “Charles Oliver N.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > > > As some of you may have heard, we’re considering disabling > > ObjectSpace.each\_object by default in JRuby. Primarily, this is for > > performance; to support each\_object, we have to bend over backwards, > > maintaining lists of weak references to all objects in the system and > > periodically cleaning out those lists. > > Is this also true for ObjectSpace#\_id2ref ? Not directly. \_id2ref is handled in a similar way, but we have an event we can trigger off to start tracking an object; namely, Object#id. When you request an id, we start tracking that object for purposes of \_id2ref. Not until. So that would not be affected by disabling ObjectSpace. In actually, however, \_id2ref is primarily used for things like weak references, so you can hold a virtual reference to an object without preventing it from being collected. We could provide an implementation of Ruby’s weak references using Java’s weak references that would allow us to escape \_id2ref entirely for that use case. Are there other places \_id2ref is used? - Charlie ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 8:59am UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/4 "2007-10-28T08:59:44Z")
From: “Charles Oliver N.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > Bill K. wrote: > > > Is this also true for ObjectSpace#\_id2ref ? > > Not directly. \_id2ref is handled in a similar way, but we have an event > we can trigger off to start tracking an object; namely, Object#id. > > When you request an id, we start tracking that object for purposes of > \_id2ref. Not until. So that would not be affected by disabling ObjectSpace. I see, thanks. Nifty. 🙂 > In actually, however, \_id2ref is primarily used for things like weak > references, so you can hold a virtual reference to an object without > preventing it from being collected. We could provide an implementation > of Ruby’s weak references using Java’s weak references that would allow > us to escape \_id2ref entirely for that use case. > > Are there other places \_id2ref is used? I think I’ve used \_id2ref exactly twice. I can’t recall the first usage; I don’t think it made it into production code. The most recent use was to store some ruby object id’s in a separate C++ process, which was able to fire an event back to ruby and provide the object id for the object to receive the event. (I suppose DRb might do something similar?) Regards, Bill ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 8:07am UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/5 "2007-10-28T08:07:10Z")
ara.t.howard wrote: > hmmm. ok i’m brainstorming here which you can ignore if you like as > i > know less that nothing about jvms or implementing ruby but here goes: > what if you could invert the problem? what i objects knew about the > global ObjectSpaceThang and could be forced to register themselves on > demand somehow? without a reference i’ve no idea how, just throwing > that out there. or, another stupid idea, what if the objects > themselves > were the tree/graph of weak references parent -\> children. crawling > it > would be, um, fun - but you could prune dead objects _only_ when > walking > the graph. this should be possible in ruby since you always have the > notion of a parent object - which is Object - so all objects should > be > either reachable or leaks. now back to drinking my regularly > scheduled > beer… Continuing this discussion here… Please, continue to brainstorm. I don’t claim to have thought out every aspect of this problem or every possible solution. I’d _love_ to discover I’ve missed an obvious fix. Your idea has come up in the past, and it would probably eliminate the cost of an ObjectSpace list. However that doesn’t appear to be where we pay the highest cost. The two items that (we believe) cost the most for us on the JVM are: - Constructing an extra object for every Ruby object…namely, the WeakReference object to point to it. So we pay a memory/allocation/initialization cost. - WeakReference itself causes Java’s GC to have to do additional checks, so it can notify the WeakReference that the object it points at has gone away. So that slows down the legendary HotSpot GC and we pay again. I believe the parent -\> weakref -\> children algorithm is used in some implementations of ObjectSpace-like behavior, so it’s perfectly valid. But again, there’s certain aspects of ObjectSpace that are just problematic… - threading or concurrency of any kind? No, you can’t have multithreading with ObjectSpace, nor a concurrent/parallel GC (and it potentially excludes other advanced GC designs too). - determinism? Matz told me that “ObjectSpace doesn’t have to be deterministic”…but when it starts getting wired into libraries like test/unit, it seems like people expect it to be. If we can say OS isn’t deterministic, then _nobody_ should be relying in its contents for core libraries, and we could reasonably claim that each\_object will never return _anything_. - Charlie ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 1:26pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/6 "2007-10-28T13:26:26Z")
Hi, At Sun, 28 Oct 2007 16:16:25 +0900, Charles Oliver N. wrote in [ruby-talk:276236]: > Are there other places \_id2ref is used? drb. ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 2:10pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/7 "2007-10-28T14:10:55Z")
On 28.10.2007 08:06, Charles Oliver N. wrote: > > notion of a parent object - which is Object - so all objects should be > > either reachable or leaks. now back to drinking my regularly scheduled > > beer… > > Continuing this discussion here… > > Please, continue to brainstorm. I don’t claim to have thought out every > aspect of this problem or every possible solution. I’d _love_ to > discover I’ve missed an obvious fix. IMHO ObjectSpace should not be implemented in Java land. Why? The JVM has to keep track of instances anyway and implementing this in Java via WeakReferences seems to duplicate functionality that is already there. Did you consider using “Java Virtual Machine Tools Interface”? > **[Java SE 6 Release Notes](https://www.oracle.com/java/technologies/javase/webnotes.html)** > > Java SE 6 Release Notes. You could either follow the same approach of the heapTracker presented on that page and use a flag or require a lib that enables ObjectSpace (because of the overhead of instrumentation). Alternatively there may be another method that does not need instrumentation and that can give you access to every (reachable) object in the JVM. > so it can notify the WeakReference that the object it points at has gone > > - determinism? Matz told me that “ObjectSpace doesn’t have to be > deterministic”…but when it starts getting wired into libraries like > test/unit, it seems like people expect it to be. If we can say OS isn’t > deterministic, then _nobody_ should be relying in its contents for core > libraries, and we could reasonably claim that each\_object will never > return _anything_. I’d reformulate the requirement here: ObjectSpace.each\_object must yield every object that was existent before the invocation and that is strongly reachable. I believe for the typical use case (e.g. traversing all class instances) this is enough while leaving enough flexibility for the implementation (i.e. create s snapshot of some form, iterate through some internal structure that may change due to new objects being created during #each\_object etc.). Kind regards robert ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 3:27pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/8 "2007-10-28T15:27:41Z")
On Oct 28, 2007, at 1:16 AM, Charles Oliver N. wrote: > Are there other places \_id2ref is used? i use it quite often as a way to have meta-programming ‘storage’ without polluting instances: foo = method :foo module\_eval \<\<-code def foo(\*a, &b) ObjectSpace.\_id2ref(#{ foo.id }).bind(self).call(\*a, &b) end code which is fabricated - but you get the concept: string in eval maps to live object at run time. when #define\_method takes a block this won’t be used much i think though… cheers. a @ [http://codeforpeople.com/](http://codeforpeople.com/) ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 5:10pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/9 "2007-10-28T17:10:41Z")
Bill K. wrote: > I think I’ve used \_id2ref exactly twice. I can’t recall the first > usage; I don’t think it made it into production code. The most > recent use was to store some ruby object id’s in a separate C++ > process, which was able to fire an event back to ruby and provide > the object id for the object to receive the event. > > (I suppose DRb might do something similar?) Yeah, sounds like that’s mostly a “poor man’s remote hash”. I’d expect that just creating a hash specifically for that purpose and passing a key around would be a “better” way to do it. \_id2ref is just another one of those features that gets rarely used, and whose use cases can often be implemented in “better” ways. - Charlie ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 2:15pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/10 "2007-10-28T14:15:02Z")
On Oct 28, 12:53 am, Charles Oliver N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > So…I’m writing this to see what the general Ruby world thinks of us > having ObjectSpace disabled by default, enableable via a command line > option (or perhaps through a library? -robjectspace?). .ext\common\win32\registry.rb:569: ObjectSpace.define\_finalizer self, @@final.call(@hkeyfinal) ext\dl\test\test.rb:187: ObjectSpace.define\_finalizer(fp) {File.unlink(“tmp.txt”)} ext\tk\lib\multi-tk.rb:493: ObjectSpace.each\_object(TclTkIp){| obj| ext\Win32API\lib\win32\registry.rb:569: ObjectSpace.define\_finalizer self, @@final.call(@hkeyfinal) lib\cgi\session.rb:299: ObjectSpace::define\_finalizer(self, Session::callback(@dbprot)) lib\drb\drb.rb:337:# object’s ObjectSpace id as its dRuby id. This means that the dRuby lib\drb\drb.rb:361: # This, the default implementation, uses an object’s local ObjectSpace lib\drb\drb.rb:375: ObjectSpace.\_id2ref(ref) lib\finalize.rb:59: ObjectSpace.call\_finalizer(obj) lib\finalize.rb:169: ObjectSpace.remove\_finalizer(@proc) lib\finalize.rb:173: ObjectSpace.add\_finalizer(@proc) lib\finalize.rb:180: # registering function to ObjectSpace#add\_finalizer lib\finalize.rb:192: ObjectSpace.add\_finalizer(@proc) lib\irb\completion.rb:152: ObjectSpace.each\_object(Module){|m| lib\irb\ext\save-history.rb:69: ObjectSpace.define\_finalizer(obj, HistorySavingAbility.create\_finalizer) lib\shell\process-controller.rb:216: ObjectSpace.each\_object(IO) do |io| lib\singleton.rb:23:# ObjectSpace.each\_object(OtherKlass){} # =\> 0. lib\singleton.rb:190: “#{ObjectSpace.each\_object(klass){}} #{klass} instance(s)” lib\tempfile.rb:53: ObjectSpace.define\_finalizer(self, @clean\_proc) lib\tempfile.rb:105: ObjectSpace.undefine\_finalizer(self) lib\tempfile.rb:118: ObjectSpace.undefine\_finalizer(self) lib\test\unit\autorunner.rb:17: ObjectSpace.each\_object(Class) do |klass| lib\test\unit\autorunner.rb:54: :objectspace =\> proc do |r| lib\test\unit\autorunner.rb:55: require ‘test/unit/collector/ objectspace’ lib\test\unit\autorunner.rb:56: c = Collector::ObjectSpace.new lib\test\unit\autorunner.rb:80: @collector = COLLECTORS[(standalone ? :dir : :objectspace)] lib\test\unit\collector\dir.rb:13: def initialize(dir=::Dir, file=::File, object\_space=::ObjectSpace, req=nil) lib\test\unit\collector\objectspace.rb:10: class ObjectSpace lib\test\unit\collector\objectspace.rb:13: NAME = ‘collected from the ObjectSpace’ lib\test\unit\collector\objectspace.rb:15: def initialize(source=::ObjectSpace) lib\test\unit.rb:252: # the ObjectSpace and wrap them up into a suite for you. It then runs lib\weakref.rb:16:# ObjectSpace.garbage\_collect lib\weakref.rb:62: ObjectSpace.\_id2ref(@\_\_id) lib\weakref.rb:74: ObjectSpace.define\_finalizer obj, @@final lib\weakref.rb:75: ObjectSpace.define\_finalizer self, @@final lib\weakref.rb:98: ObjectSpace.garbage\_collect test\dbm\test\_dbm.rb:45: ObjectSpace.each\_object(DBM) do |obj| test\gdbm\test\_gdbm.rb:42: ObjectSpace.each\_object(GDBM) do |obj| test\ruby\test\_objectspace.rb:3:class TestObjectSpace \< Test::Unit::TestCase test\ruby\test\_objectspace.rb:10: o = ObjectSpace.\_id2ref(obj.object\_id); test\sdbm\test\_sdbm.rb:15: ObjectSpace.each\_object(SDBM) do |obj| test\testunit\collector\test\_dir.rb:62: class ObjectSpace test\testunit\collector\test\_dir.rb:81: @object\_space = ObjectSpace.new test\testunit\collector\test\_objectspace.rb:6:require ‘test/unit/ collector/objectspace’ test\testunit\collector\test\_objectspace.rb:11: class TC\_ObjectSpace \< TestCase test\testunit\collector\test\_objectspace.rb:41: @c = ObjectSpace.new(@object\_space) test\testunit\collector\test\_objectspace.rb:44: def full\_suite(name=ObjectSpace::NAME) test\testunit\collector\test\_objectspace.rb:51: TestSuite.new(ObjectSpace::NAME) test\testunit\collector\test\_objectspace.rb:83: expected = TestSuite.new(ObjectSpace::NAME) test\testunit\collector\test\_objectspace.rb:89: expected = TestSuite.new(ObjectSpace::NAME) test\yaml\test\_yaml.rb:1279: ObjectSpace.each\_object(Class) do | klass| So, in summary, if we exclude those libraries where only tests are affected, this would affect: win32-registry tk cgi drb finalize irb shell singleton tempfile test-unit weakref Some comments on each of these as they relate to JRuby: win32-registry: You have no hope of implementing this without JNA anyway, unless there’s some Java binding I don’t know about. Besides, I couldn’t tell you why on Earth win32-registry would need a finalizer. tk: No one will care. They’ll use SWT or Swing bindings. Besides, you would need JNA. cgi: This could be a problem. Then again, some people say this library should be refactored or tossed. drb: This could be a big deal. finalize: Did anyone even know about this? Does anyone use it? irb: You’ve got jirb. shell: This could be a problem. singleton: Ditto. tempfile: Meh, I’m guessing Java has its own library for temp files. I never liked the current implementation anyway (which is why I wrote file-temp). test-unit: Already mentioned. weakref: You’ve stated that Java has its own implementation. Regards, Dan ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 5:20pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/11 "2007-10-28T17:20:38Z")
Robert K. wrote: > IMHO ObjectSpace should not be implemented in Java land. Why? The JVM > has to keep track of instances anyway and implementing this in Java via > WeakReferences seems to duplicate functionality that is already there. > Did you consider using “Java Virtual Machine Tools Interface”? > > [Java SE 6 Release Notes](http://java.sun.com/javase/6/webnotes/trouble/TSG-VM/html/gbmmt.html#gbmls) > > You could either follow the same approach of the heapTracker presented > on that page and use a flag or require a lib that enables ObjectSpace > (because of the overhead of instrumentation). You just hit on exactly why we don’t use JVMTI for ObjectSpace. It would certainly work, but it would add a lot of overhead we’d never expect people to accept in a real application. Plus, it would track far more object instances than we actually want tracked. We’d love to include a JVMTI-based ObjectSpace implementation, however…it just hasn’t been a high priority to implement since 99% of users never actually need ObjectSpace. > Alternatively there may be another method that does not need > instrumentation and that can give you access to every (reachable) object > in the JVM. If there is…we haven’t found it. The “linked weakref list” has been the least overhead so far, and it’s still a lot of overhead. > > checks, so it can notify the WeakReference that the object it points > > potentially excludes other advanced GC designs too). > > all class instances) this is enough while leaving enough flexibility for > > the implementation (i.e. create s snapshot of some form, iterate through > > some internal structure that may change due to new objects being created > > during #each\_object etc.). The problem here is “strongly reachable”. During ObjectSpace processing, the last strong reference to an object may go away and the garbage collector may run. Should ObjectSpace prevent GC from running if it’s traversed and now references that object? If not, how should it be handled if immediately before you return an object from each\_object, it gets garbage collected? There’s no way to catch that, so each\_object may end up returning a reference to an object that’s gone away, or reconstituting an object whose finalization has already fired. Bad things happen. ObjectSpace is just not compatible with any GC that requires the ability to move objects around in memory, run in parallel, and so on. It can _never_ be deterministic unless it can “stop the world”, so it should not be used for algorithms that require any level of determinism, such as the test search in test/unit. - Charlie ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 5:33pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/12 "2007-10-28T17:33:30Z")
Daniel B. wrote: > ext\dl\test\test.rb:187: ObjectSpace.define\_finalizer(fp) > object’s local ObjectSpace > lib\shell\process-controller.rb:216: ObjectSpace.each\_object(IO) do > lib\test\unit\autorunner.rb:54: :objectspace =\> proc do |r| > from the ObjectSpace’ > test\gdbm\test\_gdbm.rb:42: ObjectSpace.each\_object(GDBM) do |obj| > test\testunit\collector\test\_objectspace.rb:11: class > TestSuite.new(ObjectSpace::NAME) > finalize > irb > shell > singleton > tempfile > test-unit > weakref > > Some comments on each of these as they relate to JRuby: Of these, only the following would be affected, since only each\_object would be disabled by default: > tk: No one will care. They’ll use SWT or Swing bindings. Besides, you > would need JNA. > ext\tk\lib\multi-tk.rb:493: ObjectSpace.each\_object(TclTkIp){| Quite right, and there are currently no plans (or demand) for Tk support in JRuby. Swing is a far better GUI API, especially when wrapped in Ruby. > irb: You’ve got jirb. > lib\irb\completion.rb:152: ObjectSpace.each\_object(Module){|m| This could still be supported through a similar mechanism as each\_object(Class), by keeping a weak hash of all Module instances. > shell: This could be a problem. > lib\shell\process-controller.rb:216: ObjectSpace.each\_object(IO) > do I’d be surprised if shell worked 100% correctly right now anyway, due to process-control requirements we can’t support well on JVM. But I would also expect this use of each\_object to have a “better” implementation, and if not it could again be a specific-purpose weak hash for IO streams (which we almost have already since we want to be able to clean them up on exit. > singleton: Ditto. I’d have to look at this one. This could be another good candidate for reimplementation in a lot less Java code; singleton support would be pretty easy to write up in a few lines of Java. > test-unit: Already mentioned. So pretty few libraries would be affected, and I don’t think any couldn’t be dealt with in other ways. And to reiterate: finalizers and \_id2ref wouldn’t be affected (though I’d prefer to find alternative mechanisms for \_id2ref). - Charlie ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 6:13pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/13 "2007-10-28T18:13:51Z")
Ken B. wrote: > I don’t think they’re making ObjectSpace go away. Just > ObjectSpace#each\_object. Correct. > On Sun, 28 Oct 2007 22:13:38 +0900, Daniel B. wrote: > > > drb: This could be a big deal. > > weakref: You’ve stated that Java has its own implementation. > > This uses \_id2ref, which doesn’t appear to be going away. Not that I wouldn’t like it to 🙂 > > cgi: This could be a problem. Then again, some people say this library > > should be refactored or tossed. > > finalize: Did anyone even know about this? Does anyone use it? > > tempfile: Meh, I’m guessing Java has its own library for temp files. I > > never liked the current implementation anyway (which is why I wrote > > file-temp). > > Finalizers could be implemented using Java’s finalize() method for > classes that need it. This method of implementing finalizers could > probably be compatibly exposed using ObjectSpace. Correct; we do support finalizers already. They weren’t actually that hard to support, since as you say Java already supports finalization. > > shell: This could be a problem. > > This looks broken anyway since it uses fork. Ahh yes, fork is a killer. We will never, ever support fork. > > singleton: Ditto. > > one is in documentation comment, giving an example of a specific behavior > of the library. the other is in the same example, included executably > after an if **FILE** == $0 condition. So no actual problem here. Whew, that’s good to hear. I know singleton is used a bit in Rails, and most people run JRuby on Rails with ObjectSpace disabled…so this seems to fit with your findings. > > irb: You’ve got jirb. > > jirb is (at its core) still the Ruby 1.8 IRB codebase. The example you > pointed ou is class (Module) iteration, used for completion, but it’s > more general iteration than test/unit uses, and #inherited techniques > that can be used for test/unit may not work here. inherited, perhaps not. But a JRuby-internal weak list of Module instances would put this one to rest. - Charlie ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 5:55pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/14 "2007-10-28T17:55:43Z")
I don’t think they’re making ObjectSpace go away. Just ObjectSpace#each\_object. (I’m not a Jruby developer, so I don’t trust the correctness of anything I say.) On Sun, 28 Oct 2007 22:13:38 +0900, Daniel B. wrote: > drb: This could be a big deal. > weakref: You’ve stated that Java has its own implementation. This uses \_id2ref, which doesn’t appear to be going away. > cgi: This could be a problem. Then again, some people say this library > should be refactored or tossed. > finalize: Did anyone even know about this? Does anyone use it? > tempfile: Meh, I’m guessing Java has its own library for temp files. I > never liked the current implementation anyway (which is why I wrote > file-temp). Finalizers could be implemented using Java’s finalize() method for classes that need it. This method of implementing finalizers could probably be compatibly exposed using ObjectSpace. > shell: This could be a problem. This looks broken anyway since it uses fork. > singleton: Ditto. one is in documentation comment, giving an example of a specific behavior of the library. the other is in the same example, included executably after an if **FILE** == $0 condition. So no actual problem here. > irb: You’ve got jirb. jirb is (at its core) still the Ruby 1.8 IRB codebase. The example you pointed ou is class (Module) iteration, used for completion, but it’s more general iteration than test/unit uses, and #inherited techniques that can be used for test/unit may not work here. –Ken ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 6:17pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/15 "2007-10-28T18:17:26Z")
On 28.10.2007 17:19, Charles Oliver N. wrote: > > You could either follow the same approach of the heapTracker presented > > on that page and use a flag or require a lib that enables ObjectSpace > > (because of the overhead of instrumentation). > > You just hit on exactly why we don’t use JVMTI for ObjectSpace. It would > certainly work, but it would add a lot of overhead we’d never expect > people to accept in a real application. Plus, it would track far more > object instances than we actually want tracked. Why is that? I mean, you could selectively decide which instances to track. > the least overhead so far, and it’s still a lot of overhead. > Hmm, but there are iteration methods like #each\_object: > [JVM(TM) Tool Interface 1.0.38](http://java.sun.com/j2se/1.5.0/docs/guide/jvmti/jvmti.html#Heap) Did you put them down because of the “stop the world” approach? I’d say that would be ok - at least it’s better than not having ObjectSpace. And also, there would be no overhead. Question is only whether it’s ok to invoke arbitrary byte code (which would happen during the iteration callback). > > > checks, so it can notify the WeakReference that the object it points > > > potentially excludes other advanced GC designs too). > > > traversing all class instances) this is enough while leaving enough > > > flexibility for the implementation (i.e. create s snapshot of some > > > form, iterate through some internal structure that may change due to > > > new objects being created during #each\_object etc.). > > The problem here is “strongly reachable”. During ObjectSpace processing, > the last strong reference to an object may go away and the garbage > collector may run. Should ObjectSpace prevent GC from running if it’s > traversed and now references that object? If not, how should it be > handled if immediately before you return an object from each\_object, it > gets garbage collected? You are right: objects can “disappear” (i.e. loose their strong reachability) during traversal. Obviously my suggested requirement was still too strong. > There’s no way to catch that, so each\_object may > end up returning a reference to an object that’s gone away, or > reconstituting an object whose finalization has already fired. Bad > things happen. Recreation is a bad idea. I agree, objects that are no longer strongly reachable at the moment they are about to be passed to the block should _not_ be passed. > ObjectSpace is just not compatible with any GC that requires the ability > to move objects around in memory, I don’t think that moving is an issue. If it were, JVM’s would not work the way they do (object references are no pointers to memory locations). In other words, all programs would have the same problems #each\_object had. > run in parallel, and so on. It can > _never_ be deterministic unless it can “stop the world”, so it should > not be used for algorithms that require any level of determinism, such > as the test search in test/unit. Right you are. #each\_object should not be used in regular code - it’s more for ad hoc statistics (“how many instances of a class?”) and the like. Kind regards robert ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 8:08pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/16 "2007-10-28T20:08:42Z")
Quoth Daniel B.: > … > shell: This could be a problem. > … As far as I know, shell isn’t used extensively. From reading the source, it appears to be very much linked to the host system’s processes, files, etc, which may be inappropriate for JRuby anyways (I’m guessing here). Regards, ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 28, 2007, 6:40pm UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/17 "2007-10-28T18:40:50Z")
Robert K. wrote: > On 28.10.2007 17:19, Charles Oliver N. wrote: > > > You just hit on exactly why we don’t use JVMTI for ObjectSpace. It > > would certainly work, but it would add a lot of overhead we’d never > > expect people to accept in a real application. Plus, it would track > > far more object instances than we actually want tracked. > > Why is that? I mean, you could selectively decide which instances to > track. Actually, we do that a bit already. For example, we do not track arrays constructed during argument processing, since they are typically transient. The problem is that we could only choose to track all Ruby objects, for example…which would cripple other JRuby apps running in the same process. In general, though, we haven’t explored JVMTI because we want JRuby to be the best production environment for deploying apps, and nobody will EVER turn on JVMTI on their production servers. > > > Alternatively there may be another method that does not need > > > instrumentation and that can give you access to every (reachable) > > > object in the JVM. > > > > If there is…we haven’t found it. The “linked weakref list” has been > > the least overhead so far, and it’s still a lot of overhead. > > Hmm, but there are iteration methods like #each\_object: > [JVM(TM) Tool Interface 1.0.38](http://java.sun.com/j2se/1.5.0/docs/guide/jvmti/jvmti.html#Heap) I was referring to non-JVMTI solutions, but you’re right, JVMTI does provide this capability. > Did you put them down because of the “stop the world” approach? I’d say > that would be ok - at least it’s better than not having ObjectSpace. And > also, there would be no overhead. Question is only whether it’s ok to > invoke arbitrary byte code (which would happen during the iteration > callback). Is it really ok? You need to remember that JRuby opens up the possibility of running many, many applications in the same process, as well as asynchronous algorithms with true parallel threads. We can’t expect people to cripple all that so they can walk EVERY object in the system. “Stop the world” is awful when you start breaking the ability to do many things in parallel, as you can in JRuby. But it may be that for cases where each\_object is needed, this is a reasonable thing to do. I think if someone were to submit an implementation of each\_object that uses JVMTI, we would certainly accept it 🙂 > > ObjectSpace is just not compatible with any GC that requires the > > ability to move objects around in memory, > > I don’t think that moving is an issue. If it were, JVM’s would not work > the way they do (object references are no pointers to memory locations). > In other words, all programs would have the same problems #each\_object > had. The problem is not so much that the object references move as that you would have to lock the memory locations for some period of time to be able to walk the object table. And I think that’s _bad_ especially when we’re looking at JRuby allowing folks to run dozens of apps in the same process and memory space out of the box. We can’t lock things down like that. - Charlie ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 29, 2007, 4:17am UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/18 "2007-10-29T04:17:57Z")
Charles Oliver N. wrote: > Actually, we do that a bit already. For example, we do not track arrays > constructed during argument processing, since they are typically > transient. The problem is that we could only choose to track all Ruby > objects, for example…which would cripple other JRuby apps running in > the same process. […] > The problem is not so much that the object references move as that you > would have to lock the memory locations for some period of time to be > able to walk the object table. And I think that’s _bad_ especially when > we’re looking at JRuby allowing folks to run dozens of apps in the same > process and memory space out of the box. We can’t lock things down like > that. Sorry for the extremely uninitiated and naive question - but when you’re about to enumerate each object in an application, aren’t you interested only in this application’s objects anyway? So why would you have to lock anything about the other ruby apps in the same process? Is that kind of distinguishing objects impossible on the GC/enumeration level? mortee ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 29, 2007, 6:21am UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/19 "2007-10-29T06:21:12Z")
On Oct 28, 9:19 am, Charles Oliver N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > ObjectSpace is just not compatible with any GC that requires the ability > to move objects around in memory, run in parallel, and so on. It can > _never_ be deterministic unless it can “stop the world”, so it should > not be used for algorithms that require any level of determinism, such > as the test search in test/unit. This is the exact reason we haven’t yet implemented each\_object in Rubinius yet. Having a generational GC that moves objects, iterating over all objects is very, very non-deterministic unless the GC is totally turned off while objects are walked. Thats at least an option we have that we may roll with for the initial release, but it’s less than ideal. I think of each\_object as very much a MRI implementation feature that the rest of us implementors struggle to implement. Because of this, the community and core members of each implementation need to really beginning discussing whether or not each\_object is a Ruby feature or an MRI feature. - Evan ---
**Author:** ![headius](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/h/7c8e57/32.png) [@headius](https://www.ruby-forum.com/u/headius)\ **Post date:** [October 29, 2007, 4:26am UTC](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533/20 "2007-10-29T04:26:09Z")
Charles Oliver N. wrote: > I’d be surprised if shell worked 100% correctly right now anyway, due to > process-control requirements we can’t support well on JVM. But I would > also expect this use of each\_object to have a “better” implementation, > and if not it could again be a specific-purpose weak hash for IO streams > (which we almost have already since we want to be able to clean them up > on exit. Speaking of multiple cases of possible class-specific instance tracking… isn’t it possible to register your interest in some such class at some point explicitely from program code - and then any class could be made enumerable. mortee [Next page](https://www.ruby-forum.com/t/jruby-disabling-objectspace-what-implications/118533.md?page=2)