io.c (fptr_finalize): free memory before GC sweep

This releases memory on explict calls to rb_io_close,
reducing pressure on the GC.

Final massif snapshot shows reduced heap usage after RubyGems load
(valgrind --tool=massif ./ruby -e exit)

before:
	mem_heap_B=4821992
	mem_heap_extra_B=1302952

after:
	mem_heap_B=4791056
	mem_heap_extra_B=1192440

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47758 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Thu Oct  2 05:32:17 2014  Eric Wong  <e@80x24.org>
+
+	* io.c (fptr_finalize): free memory before GC sweep
+	  [ruby-core:65269] [Feature #10295]
+
 Thu Oct  2 05:27:24 2014  Eric Wong  <e@80x24.org>
 
 	* marshal.c (w_class): check dump_arg->compat_tbl before lookup

io.c

@@ -4251,6 +4251,9 @@ maygvl_fclose(FILE *file, int keepgvl)
     return (int)(intptr_t)rb_thread_call_without_gvl(nogvl_fclose, file, RUBY_UBF_IO, 0);
 }
 
+static void free_io_buffer(rb_io_buffer_t *buf);
+static void clear_codeconv(rb_io_t *fptr);
+
 static void
 fptr_finalize(rb_io_t *fptr, int noraise)
 {
@@ -4312,6 +4315,9 @@ fptr_finalize(rb_io_t *fptr, int noraise)
             rb_exc_raise(err);
         }
     }
+    free_io_buffer(&fptr->rbuf);
+    free_io_buffer(&fptr->wbuf);
+    clear_codeconv(fptr);
 }
 
 static void