Bug #9159: [patch] use rb_fstring for internal strings

• Status: Closed
• Priority: Normal
• Assignee: -
• Target version: 2.1.0
• ruby -v: ruby 2.1.0dev (2013-11-26 trunk 43852)
• Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN

[tmm1 (Aman Karmani)]

I added rb_fstring wrappers around internal strings generated by iseqs, regexps and eval:

https://github.com/tmm1/ruby/commit/9587fae171835ccf013661ba837f097754f170ef

In our rails app, this reduces the number of long-lived strings on the heap by 30%.

  $ ruby -rconfig/environment -e' GC.start; p ObjectSpace.count_objects[:T_STRING] '
  246100

  $ ruby -rconfig/environment -e' GC.start; p ObjectSpace.count_objects[:T_STRING] '
  173956

If this patch is acceptable, I can commit it. make test and test-all pass.

[tmm1 (Aman Karmani)]

One example of strings de-duplicated by this patch are iseq labels. Before:

irb(main):001:0> mm = "method_missing"
irb(main):002:0> GC.start; ObjectSpace.each_object(String).select{ |o| o == mm }.size
=> 77

After:

irb(main):002:0> GC.start; ObjectSpace.each_object(String).select{ |o| o == mm }.size
=> 3

[tmm1 (Aman Karmani)]

if (nd_type(node) == NODE_STR) {

• hide_obj(node->nd_lit);
  

• node->nd_lit = rb_fstring(node->nd_lit);
  ADD_INSN1(ret, nd_line(node), putobject, node->nd_lit);
  

Some internal strings are no longer hidden with this patch, since the underlying T_STRING object can be shared via the fstr table.
Since the object is already marked immutable (via the frozen flag), hiding it is unnecessary.

[sam.saffron (Sam Saffron)]

Seeing similar results for Discourse:

https://gist.github.com/SamSaffron/7668043

[tmm1 (Aman Karmani)]

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

This issue was solved with changeset r43866.
Aman, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• compile.c: Use rb_fstring() to de-duplicate string literals in code. [ruby-core:58599] [Bug #9159] [ruby-core:54405]
• iseq.c (prepare_iseq_build): De-duplicate iseq labels and source locations.
• re.c (rb_reg_initialize): Use rb_fstring() for regex string.
• string.c (rb_fstring): Handle non-string and already-fstr arguments.
• vm_eval.c (eval_string_with_cref): De-duplicate eval source filename.

[normalperson (Eric Wong)]

Can somebody following this thread check out my patch for
https://bugs.ruby-lang.org/issues/8998

Theoretically it should be better than nothing (but not ideal), but I
don't think any of my code uses string hash keys enough to matter...
Thanks.