diff --git a/ChangeLog b/ChangeLog
index a0cf409a37..bc193350e4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+Mon Oct 25 16:38:07 2010  URABE Shyouhei  <shyouhei@ruby-lang.org>
+
+	* signal.c  (rb_atomic_t): GCC (of  at least  recent versions)
+	  has  ubiquitos  support  for  atomic  operations.   On  that
+	  compiler a C  program can isse a memory  barrier using these
+	  dedicated  instructions.  According to  the GCC  manual they
+	  cargo culted  this feature form  the Itanium ABI  so chances
+	  are that  other compilers  could also support  this feature.
+	  But so far GCC is the  only compiler that I know to have it.
+	  Also note that this works on non-Itanium machines.
+
 Mon Oct 25 06:21:35 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* vsnprintf.c (BSD_vfprintf): prec digits fractal part should be
diff --git a/signal.c b/signal.c
index 4906e9162a..e2d9d84e4d 100644
--- a/signal.c
+++ b/signal.c
@@ -25,6 +25,17 @@ typedef LONG rb_atomic_t;
 # define ATOMIC_INC(var) InterlockedIncrement(&(var))
 # define ATOMIC_DEC(var) InterlockedDecrement(&(var))
 
+#elsif __GNUC__ >= 4
+/* @shyouhei hack to support atomic operations in case of gcc. Gcc
+ * has its own pseudo-insns to support them.  See info, or
+ * http://gcc.gnu.org/onlinedocs/gcc/Atomic-Builtins.html */
+
+typedef unsigned char rb_atomic_t; /* Anything OK */
+# define ATOMIC_TEST(var) __sync_lock_test_and_set(&(var), 0)
+# define ATOMIC_SET(var, val)  __sync_lock_test_and_set(&(var), (val))
+# define ATOMIC_INC(var) __sync_fetch_and_add(&(var), 1)
+# define ATOMIC_DEC(var) __sync_fetch_and_sub(&(var), 1)
+
 #else
 typedef int rb_atomic_t;