Commits on Jul 20, 2021

1. Use "interned" Strings when possible to avoid uneccessary heap allo… …

   …cation.
   
   Fixes ohler55#275
   
   - Background info: https://en.wikipedia.org/wiki/String_interning
   - Available to C extensions since MRI Ruby 3.0:
     - https://bugs.ruby-lang.org/issues/13381
     - https://bugs.ruby-lang.org/issues/16029
   
   This change makes `Ox` use "interned" (frozen and deduplicated) `String`s anywhere possible,
   the same effect as calling `String#-@` except without the heap churn of `RVALUE` allocation:
   https://ruby-doc.org/core/String.html#method-i-2B-40
   
   - Uses the `HAVE_<funcname>` preprocessor macros to detect this functionality
     and avoid breaking older Rubies (confirmed with at least MRI 2.7.2).
   - I explicitly use interned `String`s anywhere an allocated `String` seemed
     entirely internal to `Ox`, e.g. in `sax_value_as_time` when allocating
     the `String` argument to `ox_time_class`.
   - Adds a new user-facing option `intern_strings` to control the behavior
     of `String` return values from user-facing functions, e.g. from `sax_as_s`.
   - Results in a ~25% reduction in startup GC pressure in my library! :D
   
   Inspired by similar changes to `json` and `msgpack`:
   
   - flori/json#451
   - msgpack/msgpack-ruby#196
   
   My goal is `Object` allocation reduction in the `Ox::Sax` handler of my MIME Type
   file-identification library caused by the large number of duplicate `String`s in the
   `shared-mime-info`-format XML it uses as a data source.
   
   I was already calling `#-@` (or using the `-some_str_variable` syntax) everywhere possible
   in my handler, but that only freezes and deduplicates an already-allocated `String`:
   
     irb(main):068:0> oid = proc { puts "#{_1} is object_id #{_1.object_id}" }
     => #<Proc:0x0000564d53eb6850 (irb):66>
     irb(main):069:0> lol = 'lol'.tap(&oid).-@.tap(&oid)
     lol is object_id 19800
     lol is object_id 19740
     => "lol"
     irb(main):070:0> -lol.tap(&oid).-@.tap(&oid)
     lol is object_id 19740
     lol is object_id 19740
     => "lol"
   
   That avoids duplicate retained `String`s but still causes my library to take
   a big GC hit right at startup when it loads its data.
   
   All the stats below were collected using SamSaffron's `memory_profiler`:
   https://github.com/SamSaffron/memory_profiler
   
   First, a sanity-check to make sure I didn't break MRI < 3.0,
   using MRI 2.7 + latest official `Ox` from RubyGems (2.14.5):
   
     [okeeblow@emi#CHECKING-YOU-OUT] ruby -v
     ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-linux]
     [okeeblow@emi#CHECKING-YOU-OUT] ./bin/are-we-unallocated-yet|grep Total
     Total allocated: 20561351 bytes (401372 objects)
     Total retained:  1680971 bytes (22102 objects)
   
   versus same MRI 2.7 but with my patched `Ox`:
   
     [okeeblow@emi#CHECKING-YOU-OUT] gem install ../../ox/ox-2.14.5.gem
     [okeeblow@emi#CHECKING-YOU-OUT] ./bin/are-we-unallocated-yet|grep Total
     Total allocated: 20561111 bytes (401366 objects)
     Total retained:  1680971 bytes (22102 objects)
   
   No difference between the two, showing that this patch is a no-op for pre-3.0.
   Sorry I did not test older versions of MRI or other Rubies like J/Truffle/etc
   since I don't have them on my system.
   
   Now the real gainz can be seen when comparing MRI 3.0 with unpatched `Ox`:
   
     [okeeblow@emi#CHECKING-YOU-OUT] bundle install
     Fetching gem metadata from https://rubygems.org/......
     …
     Installing ox 2.14.5 with native extensions
     Using checking-you-out 0.7.0 from source at `.`
     Bundle complete! 11 Gemfile dependencies, 19 gems now installed.
     [okeeblow@emi#CHECKING-YOU-OUT] ./bin/are-we-unallocated-yet|grep Total
     Total allocated: 20081080 bytes (390133 objects)
     Total retained:  1713209 bytes (22095 objects)
   
   against same MRI 3.0 with my patched `Ox`:
   
     [okeeblow@emi#CHECKING-YOU-OUT] gem install ../../ox/ox-2.14.5.gem
     Building native extensions. This could take a while...
     Successfully installed ox-2.14.5
     Parsing documentation for ox-2.14.5
     unknown encoding name ""UTF-8"" for README.md, skipping
     Installing ri documentation for ox-2.14.5
     Done installing documentation for ox after 0 seconds
     1 gem installed
     [okeeblow@emi#CHECKING-YOU-OUT] ./bin/are-we-unallocated-yet|grep Total
     Total allocated: 17298804 bytes (322860 objects)
     Total retained:  1713202 bytes (22073 objects)
   
   against same MRI 3.0, my patched `Ox`, and `Ox.parse_sax(intern_strings: true)`:
   
     [okeeblow@emi#CHECKING-YOU-OUT] ./bin/are-we-unallocated-yet|grep Total
     Total allocated: 16414938 bytes (301382 objects)
     Total retained:  1713226 bytes (22073 objects)
   
   This shows that just having Ruby 3.0 available results in a huge win,
   and opting into immutable `String`s from `Value#as_s` helps me even more!
   
   Unit tests pass:
   
     [okeeblow@emi#test] ruby tests.rb
     Loaded suite tests
     Started
     .................
     16 tests, 40 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications
     100% passed
     .....
     18 tests, 42 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications
     100% passed
     ...............................................................................................................................
     151 tests, 249 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications
     100% passed
   
   Apologies for possible indentation issues in this patch. There seem to be lots of existing
   lines with a mix of tabs and spaces — nbd, it happens — so I tried to match the surrounding
   lines everywhere I made an addition to make sure things line up and look okay in `git diff`.
   
   I only use `Ox` for Sax parsing, not for marshalling, so please scrutinize my changes
   in `gen_load.c` and friends extra hard in case I omitted any `intern_strings` option
   checks that could result in an unwary user getting an immutable `String` where
   there wasn't one before. The one change I had to make to a `String#force_encoding`-using
   test case is an example of what I want to avoid surprising anyone with.

   

   okeeblow committed Jul 20, 2021
   Configuration menu

   • View commit details
   • Copy full SHA for b0d9a8e
   • Browse repository at this point

   Copy the full SHA

   b0d9a8e View commit details

   Browse the repository at this point in the history