[PATCH] unicorn_http: reduce rb_global_variable calls

[Eric Wong <e@80x24.org>]

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.
---
 ext/unicorn_http/common_field_optimization.h |  4 ++--
 ext/unicorn_http/global_variables.h          |  4 ++--
 ext/unicorn_http/httpdate.c                  |  4 ++--
 ext/unicorn_http/unicorn_http.rl             | 13 +++++++++----
 4 files changed, 15 insertions(+), 10 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);
   }
 }
 
diff --git a/ext/unicorn_http/global_variables.h b/ext/unicorn_http/global_variables.h
index e1c43c9..c17ee6a 100644
--- a/ext/unicorn_http/global_variables.h
+++ b/ext/unicorn_http/global_variables.h
@@ -56,7 +56,7 @@ NORETURN(static void parser_raise(VALUE klass, const char *));
 /** Defines global strings in the init method. */
 #define DEF_GLOBAL(N, val) do { \
   g_##N = rb_obj_freeze(rb_str_new(val, sizeof(val) - 1)); \
-  rb_global_variable(&g_##N); \
+  rb_ary_push(mark_ary, g_##N); \
 } while (0)
 
 /* Defines the maximum allowed lengths for various input elements.*/
@@ -67,7 +67,7 @@ DEF_MAX_LENGTH(FRAGMENT, 1024); /* Don't know if this length is specified somewh
 DEF_MAX_LENGTH(REQUEST_PATH, 4096); /* common PATH_MAX on modern systems */
 DEF_MAX_LENGTH(QUERY_STRING, (1024 * 10));
 
-static void init_globals(void)
+static void init_globals(VALUE mark_ary)
 {
   DEF_GLOBAL(rack_url_scheme, "rack.url_scheme");
   DEF_GLOBAL(request_method, "REQUEST_METHOD");
diff --git a/ext/unicorn_http/httpdate.c b/ext/unicorn_http/httpdate.c
index 0a1045f..2381cff 100644
--- a/ext/unicorn_http/httpdate.c
+++ b/ext/unicorn_http/httpdate.c
@@ -64,13 +64,13 @@ static VALUE httpdate(VALUE self)
 	return buf;
 }
 
-void init_unicorn_httpdate(void)
+void init_unicorn_httpdate(VALUE mark_ary)
 {
 	VALUE mod = rb_define_module("Unicorn");
 	mod = rb_define_module_under(mod, "HttpResponse");
 
 	buf = rb_str_new(0, buf_capa - 1);
-	rb_global_variable(&buf);
+	rb_ary_push(mark_ary, buf);
 	buf_ptr = RSTRING_PTR(buf);
 	httpdate(Qnil);
 
diff --git a/ext/unicorn_http/unicorn_http.rl b/ext/unicorn_http/unicorn_http.rl
index 957a5e3..6fc3498 100644
--- a/ext/unicorn_http/unicorn_http.rl
+++ b/ext/unicorn_http/unicorn_http.rl
@@ -13,7 +13,7 @@
 #include "global_variables.h"
 #include "c_util.h"
 
-void init_unicorn_httpdate(void);
+void init_unicorn_httpdate(VALUE mark_ary);
 
 #define UH_FL_CHUNKED  0x1
 #define UH_FL_HASBODY  0x2
@@ -917,8 +917,10 @@ static VALUE HttpParser_rssget(VALUE self)
 
 void Init_unicorn_http(void)
 {
+  static VALUE mark_ary;
   VALUE mUnicorn, cHttpParser;
 
+  mark_ary = rb_ary_new();
   mUnicorn = rb_define_module("Unicorn");
   cHttpParser = rb_define_class_under(mUnicorn, "HttpParser", rb_cObject);
   eHttpParserError =
@@ -928,7 +930,7 @@ void Init_unicorn_http(void)
   e414 = rb_define_class_under(mUnicorn, "RequestURITooLongError",
                                eHttpParserError);
 
-  init_globals();
+  init_globals(mark_ary);
   rb_define_alloc_func(cHttpParser, HttpParser_alloc);
   rb_define_method(cHttpParser, "initialize", HttpParser_init, 0);
   rb_define_method(cHttpParser, "clear", HttpParser_clear, 0);
@@ -964,14 +966,17 @@ void Init_unicorn_http(void)
 
   rb_define_singleton_method(cHttpParser, "max_header_len=", set_maxhdrlen, 1);
 
-  init_common_fields();
+  init_common_fields(mark_ary);
   SET_GLOBAL(g_http_host, "HOST");
   SET_GLOBAL(g_http_trailer, "TRAILER");
   SET_GLOBAL(g_http_transfer_encoding, "TRANSFER_ENCODING");
   SET_GLOBAL(g_content_length, "CONTENT_LENGTH");
   SET_GLOBAL(g_http_connection, "CONNECTION");
   id_set_backtrace = rb_intern("set_backtrace");
-  init_unicorn_httpdate();
+  init_unicorn_httpdate(mark_ary);
+
+  OBJ_FREEZE(mark_ary);
+  rb_global_variable(&mark_ary);
 
 #ifndef HAVE_RB_HASH_CLEAR
   id_clear = rb_intern("clear");
-- 
EW