string.c: mark frozen string

* string.c (rb_fstring): because of lazy sweep, str may be unmaked
  already and swept at next time, so mark it for the time being.
  [ruby-core:57756]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43210 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 3 insertions, 0 deletions

diff --git a/string.c b/string.c
index 7bf4006fdf..6512fe4092 100644
--- a/string.c
+++ b/string.c
@@ -146,6 +146,9 @@ rb_fstring(VALUE str)
     st_data_t fstr;
     if (st_lookup(frozen_strings, (st_data_t)str, &fstr)) {
 	str = (VALUE)fstr;
+	/* because of lazy sweep, str may be unmaked already and swept
+	 * at next time */
+	rb_gc_mark(str);
     }
     else {
 	str = rb_str_new_frozen(str);