最近一直忙Storm相关的东西,今天抽时间整理一下Erlang笔记,这一次的内容主要是一些开源项目:Mock ,worker pool......
  
 

安装Erlan/OTP

  
 之前写过一个关于Centos安装Erlang的文章,还是有人把Erlang编译安装这件事情做到了极致:Kerl
 
  Easy building and installing of Erlang/OTP instances;Kerl aims to be shell agnostic and its only dependencies, excluding what's required to actually build Erlang/OTP, are curl and git.
 
$ kerl list releases
Getting the available releases from erlang.org...
R10B-0 R10B-2 R10B-3 R10B-4 R10B-5 R10B-6 R10B-7 R10B-8 R10B-9 R11B-0 R11B-1
R11B-2 R11B-3 R11B-4 R11B-5 R12B-0 R12B-1 R12B-2 R12B-3 R12B-4 R12B-5 R13A
R13B R13B01 R13B02 R13B03 R13B04 R14A R14B R14B01 R14B02
Run "./kerl update releases" to update this list from erlang.org

 

  

2013-6-1 18:33:47更新 网友Wang Lihe的使用反馈,供参考

缘起是这样:在公司开发项目,但是公司使用的redhat很老旧,只有5.3至5.8系列的,甚至还有4系列。官方库里是没有erlang的,于是epel。但是epel 5里面只R12,版本相当的老。于是忍着各种基础不足(比如lists模块居然都少几个函数,binary根本没有,rebar要求R13以上啊),开发功能。但是干到第二版时,基本的性能已经达到极限了,<<160000个>>的解析变换居然要100几个毫秒,坚决不能同意。于是开始加入driver和nif。结果发现R14B才是nif真正可用的,R12根本没这个接口,头撞墙啊,俩小弟那无助的眼神啊,我只好放下功能,开始研究epel 6的rpm包(邪路,不小心中招,费力不讨好,没有成功编译过,而且分成十几个小包,巨细,且讨厌)。猛然间发现,给erlang epel打包的俄国哥们其实已经给epel5打了R14B的包,只是redhat官方喜欢“稳定”(我怀疑就是想让全世界开发新功能赶快升级就对了),进不去。不管怎么说,R14B成功进入开发系统。但是问题很快又出现了,这大哥打的包,不知是真的因为redhat太老,还是有失水准,R14B是没有HIPE的,而且所有的lib的src都是空的,这让我们开发挖源码时不胜烦恼。于是一边开发,一边还是在研究打包。一开始是看着erlang-solutions的rhel5.5 coming soon眼发绿,但是好久没有动静,后来开始看官方编译教程,猛然间,搜到了一个叫kerl的东西。这让我大喜过望,试用结果非常好。kerl本身只是一个shell脚本,运行后在$HOME下建立.kerl目录,所有的东西都放下面,不会扰乱其他的,而且从下载到编译安装一就俱全,特特别好的是,安装并不需要安装到系统,而是可以指定自己的位置,这样,可以同时安装好多个版本。只要引入不同的启动文件,就可以在不同的erlang版本里切换,非常方便。我一路从R14B编译至R16B,全部成功,哇卡卡,甚至可以在rhel4上使用,这是让公司的老机器焕发青春么(磁盘满了,编译过了,好像没安装成功,有机会再重试,有成功的各位分享一下)?至此,在合适的时候,所有的开发和应用环境,都有机会使用最新版erlang了,以上,分享给各位。

各种网址:
epel: https://fedoraproject.org/wiki/EPEL
以前上面还有4系列的,rhel4上的erlang是R11,完全不能用。
rhel4系列的源还活着https://dl.fedoraproject.org/pub/epel/4/x86_64/,

俄国大哥的博客:https://lemenkov.wordpress.com/2010/11/07/erlang-otp-r14b-for-epel-5/
提到的rhel5上的r14b的源:http://repos.fedorapeople.org/repos/peter/erlang/

 

 

Erlang 多语言混搭

  
   Erlang和其它语言混搭一下,效果如何?有不少这样的项目,有些纯属玩票,有的还是发展的不错;
 
Reia 
     Reia就属于玩票的那种,no realease ! no direct download links!
 
 Reia is a Ruby-like scripting language for the Erlang virtual machine. Reia brings you the best of both worlds between Ruby's friendly syntax, reflection, metaprogramming, and the amazing power of blocks, and Erlang's immense abilities for concurrency, distribution, hot code swapping, and fault tolerance.
Reia's source code is available on Github. There are no releases and thus no direct download links yet, sorry! See the README on Github for instructions on how to build Reia from source.
 
 项目地址: http://reia-lang.org/
 
 
Erlang Meet Javascript
  
   Node.js着实让Javascript又火了一把 ,Erlang与Javascript又会擦出什么火花? 看看

 
 
Elixir
  发展比较不错的就属Elixir了,周边的项目也越来越多;
 
   Elixir is a functional meta-programming aware language built on top of the Erlang VM. It is a dynamic language with flexible syntax with macros support that leverages Erlang's abilities to build concurrent, distributed, fault-tolerant applications with hot code upgrades.
 
复制代码
defmodule Hello do
  IO.puts "Defining the function world"

  def world do
    IO.puts "Hello World"
  end

  IO.puts "Function world defined"end

Hello.world
复制代码

项目地址: http://elixir-lang.org/

相关链接: http://expm.co/
 
 
Lua
 
Luerl - an implementation of Lua in Erlang  https://github.com/rvirding/luerl
 
Joxa
 
A Modern Lisp for the Erlang VM https://github.com/ericbmerritt/joxa
 

Meck

 
    做测试Mock是利器,Erlang对应的解决方案是meck:
    With meck you can easily mock modules in Erlang. You can also perform some basic validations on the mocked modules, such as making sure no unexpected exceptions occurred or looking at the call history.
 
看看下面的例子是不是都是熟悉的东西:
   
复制代码
Eshell V5.8.4  (abort with ^G)
1> meck:new(dog).
ok
2> meck:expect(dog, bark, fun() -> "Woof!" end).
ok
3> dog:bark().
"Woof!"
4> meck:validate(dog).
true
5> meck:unload(dog).
ok
6> dog:bark().
** exception error: undefined function dog:bark/0

7> meck:expect(dog, meow, fun() -> meck:exception(error, not_a_cat) end).
ok
8> catch dog:meow().
{'EXIT',{not_a_cat,[{meck,exception,2},
                    {meck,exec,4},
                    {dog,meow,[]},
                    {erl_eval,do_apply,5},
                    {erl_eval,expr,5},
                    {shell,exprs,6},
                    {shell,eval_exprs,6},
                    {shell,eval_loop,3}]}}
9> meck:validate(dog).
true
复制代码

 

 项目地址: https://github.com/eproxus/meck

 还有一个gen_server_mock.erl 也可以看一下: https://github.com/jashmenn/gen_server_mock

 

 Poolboy 

 
    正如这个项目的描述 "A hunky Erlang worker pool factory"
复制代码
init([]) ->
    {ok, Pools} = application:get_env(example, pools),
    PoolSpecs = lists:map(fun({Name, SizeArgs, WorkerArgs}) ->
        PoolArgs = [{name, {local, Name}},
                    {worker_module, example_worker}] ++ SizeArgs,
        poolboy:child_spec(Name, PoolArgs, WorkerArgs)
    end, Pools),
    {ok, {{one_for_one, 10, 10}, PoolSpecs}}.

squery(PoolName, Sql) ->
    poolboy:transaction(PoolName, fun(Worker) ->
        gen_server:call(Worker, {squery, Sql})
    end).

equery(PoolName, Stmt, Params) ->
    poolboy:transaction(PoolName, fun(Worker) ->
        gen_server:call(Worker, {equery, Stmt, Params})
    end).
复制代码
 
 
 
 
常识一则:获取gen_server gen_fsm的运行时Status
 
   这应该算是常识不算技巧了,使用sys:get_status/1,可以获取gen_server等运行时的值.下面是process_info和sys:get_status的结果对比;这里使用的fsm_demo.erl是一个gen_fsm的程序.记录一下,我总是忘记它所在的模块;
 
复制代码
Eshell V5.9  (abort with ^G)
1> fsm_demo:start(abc).
{ok,<0.34.0>}
2> {_,Pid}=v(1).
{ok,<0.34.0>}
3> erlang:process_info(Pid).
[{registered_name,fsm_demo},
{current_function,{gen_fsm,loop,7}},
{initial_call,{proc_lib,init_p,5}},
{status,waiting},
{message_queue_len,0},
{messages,[]},
{links,[]},
{dictionary,[{'$ancestors',[<0.32.0>]},
              {'$initial_call',{fsm_demo,init,1}}]},
{trap_exit,false},
{error_handler,error_handler},
{priority,normal},
{group_leader,<0.25.0>},
{total_heap_size,233},
{heap_size,233},
{stack_size,10},
{reductions,20},
{garbage_collection,[{min_bin_vheap_size,46368},
                      {min_heap_size,233},
                      {fullsweep_after,65535},
                      {minor_gcs,0}]},
{suspending,[]}]
4> sys:get_status(fsm_demo).
{status,<0.34.0>,
        {module,gen_fsm},
        [[{'$ancestors',[<0.32.0>]},
          {'$initial_call',{fsm_demo,init,1}}],
         running,<0.34.0>,[],
         [{header,"Status for state machine fsm_demo"},
          {data,[{"Status",running},
                 {"Parent",<0.34.0>},
                 {"Logged events",[]},
                 {"StateName",locked}]},
          {data,[{"StateData",{[],abc}}]}]]}
5> 
复制代码

 

2012年12月18日 14:10:24 补记

复制代码
Eshell V5.9  (abort with ^G)
1>  T={a,12,"good_man",<<2,3,4>>}.
{a,12,"good_man",<<2,3,4>>}
2> io:format("Data Dump:~p",[T]).
Data Dump:{a,12,"good_man",<<2,3,4>>}ok
3> rd(a,{age,name,desc}).
a
4> io:format("Data Dump:~p",[T]).
Data Dump:{a,12,"good_man",<<2,3,4>>}ok
5> T2=T.
#a{age = 12,name = "good_man",desc = <<2,3,4>>}
6> io:format("Data Dump:~p",[T2]).
Data Dump:{a,12,"good_man",<<2,3,4>>}ok
7> io:format(io_lib_pretty:print(T, fun(a, 3) -> [age,name,desc] end)).
#a{age = 12,name = "good_man",desc = <<2,3,4>>}ok
8> 
复制代码

 

2012-12-19 21:55 补记

 今天群里面有人问到:一个进程被压了很多消息,处理速度变慢,开启了SMP更慢,何解?

 这个和timer的情况很类似:

Creating timers using erlang:send_after/3 and erlang:start_timer/3 is much more efficient than using the timers provided by the timer module. The timer module uses a separate process to manage the timers, and that process can easily become overloaded if many processes create and cancel timers frequently (especially when using the SMP emulator).

http://www.erlang.org/doc/efficiency_guide/commoncaveats.html#id62547

 

 

 

最后小图一张: