Feature #9190: Expose serial helper macros

• Status: Closed
• Assignee: -
• Target version: -

[simeonwillbanks (Simeon Willbanks)]

I've defined RubyVM::InstructionHelper with singleton methods #method_serial and #constant_serial. They delegate to helper macros GET_METHOD_SERIAL() and GET_CONSTANT_SERIAL().

With these methods, users have visibility into the method and constant caches. If it makes sense, I hope this patch is included in Ruby 2.1.0.

def constants_busted?(&blk)
starting = RubyVM::InstructionHelper.constant_serial
yield
ending = RubyVM::InstructionHelper.constant_serial
ending > starting
end

busted = constants_busted? do
class Foo; end
end
puts busted.inspect

true

https://github.com/ruby/ruby/pull/462.patch

Thanks for considering; any input is appreciated!

[simeonwillbanks (Simeon Willbanks)]

After addressing a Pull Request comment, the methods are defined on RubyVM:

RubyVM.method_serial
RubyVM.constant_serial

[nobu (Nobuyoshi Nakada)]

• Category set to core
• % Done changed from 100 to 0

Why do you need those internal values?

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Feedback

Why do you need those internal values?

We have something similar in our custom build of Ruby. It's very useful for performance metrics.

[tmm1 (Aman Karmani)]

I would like to see these exposed as well. They provide visibility into VM behavior, and are very useful for measuring how many constant or method table invalidations are happening in large applications.

[simeonwillbanks (Simeon Willbanks)]

@charliesome and @tmm1 (Aman Karmani), thanks for the support, and I concur.

@nobu (Nobuyoshi Nakada) I've hacked together a gem. It's an alpha version, and it depends upon this patch.

https://github.com/simeonwillbanks/busted

The gem is a continuation of the description's example. Basically, an application wraps code in a block. Once the block executes, it reports whether or not the constant or method cache was busted. The tests have specific examples.

https://github.com/simeonwillbanks/busted/blob/master/test/busted_test.rb

Hope this helps. If you have anymore questions, please ask. Thanks!

[tmm1 (Aman Karmani)]

My main use-case for exposing these serials is to collect them automatically before and after each request in a rails app and graph how many times the caches are busted per request.

I would also like to see a Tracepoint or other hook that fires whenever the cache is busted. This would allow capturing a stack trace to see exactly where the cache busting is happening.

[tmm1 (Aman Karmani)]

If we're opposed to adding multiple methods to RubyVM, maybe a RubyVM.stat will suffice. It can behave the same way that GC.stat does (optional hash argument to avoid allocations).

[simeonwillbanks (Simeon Willbanks)]

I'm cool with RubyVM.stat; copying the GC.stat implementation is a good idea.

RubyVM.stat
=> {
:method_serial => 200,
:constant_serial => 210,
}

[nobu (Nobuyoshi Nakada)]

It sounds better than exposing those values directly.

[simeonwillbanks (Simeon Willbanks)]

OK, cool. I'll refactor the Pull Request. Thanks!

[tmm1 (Aman Karmani)]

• Status changed from Feedback to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r44062.
Simeon, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

vm.c: add RubyVM.stat for accessing cache serials

• vm.c (ruby_vm_stat): add RubyVM.stat() for access to internal cache
  counters. this methods behaves like GC.stat, accepting an optional
  hash or symbol argument. [Bug #9190] [ruby-core:58750]
• test/ruby/test_rubyvm.rb: test for new method

[simeonwillbanks (Simeon Willbanks)]

Thanks everyone!