unicorn_http: reduce rb_global_variable calls

rb_global_variable registers the address of the variable which
refers to the object, instead of the object itself.  This adds
extra overhead to each global variable for our case, where the
variable is frozen and never changed.

Given there are currently 59 elements in this array, this saves
58 singly-linked list entries and associated malloc calls and
associated overhead in the current mainline Ruby 2.x
implementation.  On 64-bit GNU libc malloc, this is already
16 * 58 = 928 bytes; more than the extra object slot and array
slack space used by the new mark array.

Mainline Ruby 1.9+ currently has a rb_gc_register_mark_object
public function which would suite our needs, too, but it is
currently undocumented, and may not be available in the future.

1 files changed, 2 insertions, 2 deletions

diff --git a/ext/unicorn_http/common_field_optimization.h b/ext/unicorn_http/common_field_optimization.h
index 42c5430..251e734 100644
--- a/ext/unicorn_http/common_field_optimization.h
+++ b/ext/unicorn_http/common_field_optimization.h
@@ -60,7 +60,7 @@ static struct common_field common_http_fields[] = {
 #define HTTP_PREFIX_LEN (sizeof(HTTP_PREFIX) - 1)
 
 /* this function is not performance-critical, called only at load time */
-static void init_common_fields(void)
+static void init_common_fields(VALUE mark_ary)
 {
   int i;
   struct common_field *cf = common_http_fields;
@@ -77,7 +77,7 @@ static void init_common_fields(void)
       cf->value = rb_str_new(tmp, HTTP_PREFIX_LEN + cf->len);
     }
     cf->value = rb_obj_freeze(cf->value);
-    rb_global_variable(&cf->value);
+    rb_ary_push(mark_ary, cf->value);
   }
 }