add simple hot swap

README.md

@@ -1,11 +1,12 @@
-#summary
-one example, show how to swap erlang code online include inner state record 
+#Example1
+
+show how to swap erlang code online include inner state record 
 
 first, we have gen server swap_test
 this is counter program, each call will show inner state counter, than incrment this counter.
 now, we need change code, can set random step, but gen process cant stop, so need online swap code
 
-#step
+##step
 
 >os:cmd("cp swap_test1.erl swap_test.erl").
 
@@ -37,3 +38,60 @@ now, we need change code, can set random step, but gen process cant stop, so nee
 
 now we set step = 3
 
+
+##code 
+
+
+you can see this blog for [detail](http://www.hoterran.info/erlang-otp-sys-sourcecode)
+
+
+#Example2
+
+
+how to kill old code process
+
+    1> c(e3).
+    {ok,e3}
+    2> e3:start().
+    true
+    3> whereis(e3).
+    <0.41.0>
+    4> c(e3).
+    {ok,e3}
+    5> whereis(e3).
+    <0.41.0>
+    6> c(e3).
+    {ok,e3}
+    7> whereis(e3).
+    undefined
+
+the second c(e3) kill old code process
+
+#Example3
+
+##upgrade
+
+>> c(e3).
+{ok,e3}
+>> e3:start().
+true
+>> e3:msg().
+"aa"
+hello
+
+modify code ``aa`` to ``bb``
+
+>> e3:compile().
+{module,e3}
+>> e3:msg(). 
+hello
+"aa"
+
+yes cant change, still old code, now switch
+
+>> e3:switch().
+code_switch
+8> e3:msg(). 
+"bb"
+hello
+

e3.erl

@@ -0,0 +1,25 @@
+-module(e3).
+-compile(export_all).
+
+start() ->
+	register(?MODULE, spawn(?MODULE, loop, [])).
+
+switch() ->
+	?MODULE ! code_switch.
+
+compile() ->
+	compile:file(?MODULE),
+	code:purge(?MODULE),
+	code:load_file(?MODULE).
+
+msg() ->
+	?MODULE ! hello.
+
+loop() ->
+    receive
+        code_switch ->
+            ?MODULE:loop();
+        _ ->
+			io:format("~p~n", ["bb"]),
+            loop()
+    end.