erlang作为一个为电信级别而出现的语言,热更新是其最重要的特性之一
热代码升级-Erlang允许程序代码在运行系统中被修改。旧代码能被逐步淘汰而后被新代码替换。在此过渡期间,新旧代码是共存的。
下面我们以最典型的gen_server为例子,讲解一下这个BT的功能
-module(tt13). -behaviour(gen_server). -export([test/0]). -export([start_link/0, stop/0, init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]). -record(state, {cnt}). -define(SERVER, ?MODULE). %%-------------------------------------------------------------------- %% Function: start_link() -> {ok,Pid} | ignore | {error,Error} %% Description: Starts the server %%-------------------------------------------------------------------- start_link() -> gen_server:start_link({local, ?MODULE}, ?MODULE, [], [{debug, [trace]}]). test() -> gen_server:call(?SERVER, test). stop() -> gen_server:cast(?SERVER, stop). %%-------------------------------------------------------------------- %% Function: init(Args) -> {ok, State} | %% {ok, State, Timeout} | %% ignore | %% {stop, Reason} %% Description: Initiates the server %%-------------------------------------------------------------------- init(_) -> {ok, #state{cnt=1}}. %%-------------------------------------------------------------------- %% Function: %% handle_call(Request, From, State) -> {reply, Reply, State} | %% {reply, Reply, State, Timeout} | %% {noreply, State} | %% {noreply, State, Timeout} | %% {stop, Reason, Reply, State} | %% {stop, Reason, State} %% Description: Handling call messages handle_call(test, _From, #state{cnt=Cnt} = State) -> {reply, {ok, Cnt}, State#state{cnt=Cnt+1}}; handle_call(stop, _From, State) -> {stop, normal, ok, State}; handle_call(_Unrec, _From, State) -> {reply, {error, invalid_call}, State}. %%-------------------------------------------------------------------- %% Function: handle_cast(Msg, State) -> {noreply, State} | %% {noreply, State, Timeout} | %% {stop, Reason, State} %% Description: Handling cast messages %%-------------------------------------------------------------------- handle_cast(_Msg, State) -> {noreply, State}. %%-------------------------------------------------------------------- %% Function: handle_info(Info, State) -> {noreply, State} | %% {noreply, State, Timeout} | %% {stop, Reason, State} %% Description: Handling all non call/cast messages %%-------------------------------------------------------------------- handle_info(_Info, State) -> {noreply, State}. %%-------------------------------------------------------------------- %% Function: terminate(Reason, State) -> void() %% Description: This function is called by a gen_server when it is about to %% terminate. It should be the opposite of Module:init/1 and do any necessary %% cleaning up. When it returns, the gen_server terminates with Reason. %% The return value is ignored. %%-------------------------------------------------------------------- terminate(_Reason, _State) -> io:format("hello gen server: terminating~n"). %%-------------------------------------------------------------------- %% Func: code_change(OldVsn, State, Extra) -> {ok, NewState} %% Description: Convert process state when code is changed %%-------------------------------------------------------------------- code_change(_OldVsn, State, _Extra) -> {ok, State}. %%==================================================================== %%other fun %%====================================================================
编译运行结果
1> c(tt13). {ok,tt13} 2> tt13:start_link(). {ok,<0.39.0>} 3> tt13:test(). *DBG* tt13 got call test from <0.32.0> *DBG* tt13 sent {ok,1} to <0.32.0>, new state {state,2} {ok,1} 4> tt13:test(). *DBG* tt13 got call test from <0.32.0> *DBG* tt13 sent {ok,2} to <0.32.0>, new state {state,3} {ok,2} 5> tt13:test(). *DBG* tt13 got call test from <0.32.0> *DBG* tt13 sent {ok,3} to <0.32.0>, new state {state,4} {ok,3}
如果修改了函数,可以直接运行
-module(tt13). -version("1.1"). -behaviour(gen_server). %........... %...........省略若干行 %................ handle_call(test, _From, #state{cnt=Cnt} = State) -> {reply, {ok, Cnt}, State#state{cnt=Cnt*2}}; %........... %...........省略若干行 %................
可以看到我们修改了计数的方法,而且修改了版本号,然后我们继续运行
6> c(tt13). %编译新的代码 {ok,tt13} 7> tt13:test(). *DBG* tt13 got call test from <0.32.0> *DBG* tt13 sent {ok,4} to <0.32.0>, new state {state,8} {ok,4} 8> tt13:test(). *DBG* tt13 got call test from <0.32.0> *DBG* tt13 sent {ok,8} to <0.32.0>, new state {state,16} {ok,8} 9> tt13:test(). *DBG* tt13 got call test from <0.32.0> *DBG* tt13 sent {ok,16} to <0.32.0>, new state {state,32} {ok,16}
可以看到代码就直接替换了,注意编译的时候会用新的代码替换下一次运行的结果,正在运行还是old code,所以不要编译多次(一般在测试环境先进行热更新测试)。
如果要替换init/1里面的代码?这个方法肯定是不行的,因为init/1代码只运行一次,比如我要修改state结构体,那要怎么弄呢
-module(tt13). -version("2.0"). -behaviour(gen_server). -record(state, {testcheck, cnt}).
%........... %...........省略若干行 %................
init(_) -> {ok, #state{testcheck=‘chk‘, cnt=1}}. %%-------------------------------------------------------------------- %% Function: %% handle_call(Request, From, State) -> {reply, Reply, State} | %% {reply, Reply, State, Timeout} | %% {noreply, State} | %% {noreply, State, Timeout} | %% {stop, Reason, Reply, State} | %% {stop, Reason, State} %% Description: Handling call messages handle_call(test, _From, #state{cnt=Cnt} = State) -> {reply, {ok, Cnt}, State#state{cnt=Cnt+1}};
%........... %...........省略若干行 %................
原文地址:https://www.cnblogs.com/tudou008/p/9473639.html
时间: 2024-10-11 05:21:52