Process.warmup: precompute strings coderange

This both save time for when it will be eventually needed,
and avoid mutating heap pages after a potential fork.

Instrumenting some large Rails app, I've witnessed up to
58% of String instances having their coderange still unknown.

process.c

@@ -8535,6 +8535,27 @@ static VALUE rb_mProcUID;
 static VALUE rb_mProcGID;
 static VALUE rb_mProcID_Syscall;
 
+
+static int
+proc_warmup_each_object(void *vstart, void *vend, size_t stride, void *data)
+{
+ VALUE v = (VALUE)vstart;
+ for (; v != (VALUE)vend; v += stride) {
+ switch (BUILTIN_TYPE(v)) {
+ case T_STRING:
+ // precompute the string coderange. This both save time for when it will be
+ // eventually needed, and avoid mutating heap pages after a potential fork.
+ rb_enc_str_coderange(v);
+ break;
+ default:
+ break;
+ }
+ }
+
+ return 0;
+}
+
+
 /*
  * call-seq:
  * Process.warmup -> true
@@ -8563,10 +8584,12 @@ proc_warmup(VALUE _)
  RB_VM_LOCK_ENTER();
  rb_gc_prepare_heap();
  RB_VM_LOCK_LEAVE();
+
+ rb_objspace_each_objects(proc_warmup_each_object, NULL);
+
  return Qtrue;
 }
 
-
 /*
  * Document-module: Process
  *

test/ruby/test_process.rb

@@ -2709,4 +2709,16 @@ def test_warmup_run_major_gc_and_compact
  assert_equal compact_count + 1, GC.stat(:compact_count)
  end;
  end
+
+ def test_warmup_precompute_string_coderange
+ assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
+ require 'objspace'
+ begin;
+ obj = "a" * 12
+ obj.force_encoding(Encoding::BINARY)
+ assert_includes(ObjectSpace.dump(obj), '"coderange":"unknown"')
+ Process.warmup
+ assert_includes(ObjectSpace.dump(obj), '"coderange":"7bit"')
+ end;
+ end
 end