Erlang經常使用代碼段

時間 2019-11-08

標籤 erlang 經常使用代碼段简体版

原文原文鏈接

十六進制字符串轉爲二進制app

hex_to_bin(Bin) ->  
    hex2bin(Bin).

hex2bin(Bin) when is_binary(Bin) ->
    hex2bin(binary_to_list(Bin));
hex2bin([]) ->
    <<>>;
hex2bin([X, Y | Rest]) ->
    <<(erlang:list_to_integer([X], 16) * 16 + erlang:list_to_integer([Y], 16)):8, (hex2bin(Rest))/binary>>.

二進制轉爲十六進制字符串函數

bin2hex(B) ->
    bin2hex(B, lower).

bin2hex(B, LowerOrUpper) when is_binary(B) ->
    bin2hex(binary_to_list(B), LowerOrUpper);
bin2hex(L, upper) ->
    LH0 = lists:map(fun(X) -> erlang:integer_to_list(X, 16) end, L),
    LH = lists:map(fun([X, Y]) -> [X, Y]; ([X]) -> [$0, X] end, LH0),
    lists:flatten(LH);
bin2hex(B, lower) ->
    H = bin2hex(B, upper),
    string:to_lower(H).

反編譯代碼
有時候線上出問題的時候，須要查看線上運行的代碼，這時候就用到反編譯了。工具

decompile(Mod) ->
    {ok, {_, [{abstract_code, {_, AC}}]}} = beam_lib:chunks(code:which(Mod), [abstract_code]),
    try
        io:format("~s~n", [erl_prettypr:format(erl_syntax:form_list(AC))])
    catch
        io:format("~ts~n", [erl_prettypr:format(erl_syntax:form_list(AC))])
    end.

分裂進程
erlang分裂進程的函數是erlang:spawn。選項有oop

spawn(Fun) -> pid()
spawn(Node, Fun) -> pid() %若是Node不存在，返回一個無用的pid
spawn(Module, Function, Args) -> pid()
spawn(Node, Module, Function, Args) -> pid()
spawn_link(Fun) -> pid()
spawn_link(Node, Fun) -> pid()
spawn_link(Module, Function, Args) -> pid()
spawn_link(Node, Module, Function, Args) -> pid()
spawn_monitor(Fun) -> {pid(), reference()}
spawn_monitor(Module, Function, Args) -> {pid(), reference()}
spawn_opt(Fun, Options) -> pid() | {pid(), reference()}
spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()}
spawn_opt(Module, Function, Args, Options) -> pid() | {pid(), reference()}
spawn_opt(Node, Module, Function, Args, Options) -> pid() | {pid(), reference()}
Options = [Option]
Option = 
    link |
    monitor | 
    {priority, Level :: priority_level()} |
    {fullsweep_after, Number :: integer() >= 0} |
    {min_heap_size, Size :: integer() >= 0} |
    {min_bin_vheap_size, VSize :: integer() >= 0}
    priority_level() = low | normal | high | max

link: 父進程與子進程創建鏈接
monitor: 父進程監控子進程
{priority, Level}: 設置新的進程的優先級。等價於在新進程中執行process_flag(priority, Level)。區別在於，spawn的時候設置優先級，優先級會在進程被選擇運行以前就設置好了。
{fullsweep_after, Number}：只是用在調整性能上。Erlang的運行系統，使用的是分代的垃圾回收機制。用一個『old heap』保存至少存活了一個垃圾回收週期的數據，當old heap空間不夠時，就會執行垃圾回收。
{min_heap_size, Size}，只是用在調整性能上。設置heap的最小size，單位是word。將這個值設置的比系統默認的大的話，會加速一些進程運行，由於會減小垃圾回收的執行次數。可是太大會致使內存不夠，減慢系統運行。
{min_bin_vheap_size, VSize},只是用在調整性能上。

交叉引用工具：xref。xref經過分析函數的調用和定義，發現函數、模塊、應用和版本之間的依賴關係。這個工具能夠幫助查看是否有函數名輸入錯誤。在用rebar打包時，能夠用rebar xref執行。性能

得到ps命令獲得的消耗的內存ui

get_ps_real_memory() ->
    Cmd = "pid=`echo $$`;p=`ps -ef | awk -v pid=$pid '$2 == pid {print $3}'`;mem=`ps -o rss -p $p | grep -v RSS`;r=$(($mem/1024));echo $r",
    os:cmd(Cmd),
    Result = os:cmd(Cmd),
    string:substr(Result, 1, length(Result) - 1).

得到top命令獲得的消耗的內存spa

get_top_real_memory() ->
    Cmd = "pid=`echo $$`;p=`ps -ef | awk -v pid=$pid '$2 == pid {print $3}'`;mem=`cat /proc/$p/stat | awk '{print $24}'`;r=$(($mem*4096/1024/1024));echo $r",
    Result = os:cmd(Cmd),
    case length(Result) > 1 of
        true ->
            string:substr(Result, 1, length(Result) -1);
        false ->
            0
    end.

得到當前cpu的核數code

get_cpu_count() ->
    Cmd = "cat /proc/cpuinfo | grep processor | wc -l",
    R = os:cmd(Cmd),
    case string:to_integer(R) of
        {Count, _} when is_integer(Count) -> Count;
        {error, _} -> 0
    end.

得到ps命令獲得的虛擬內存消耗orm

get_ps_virtual_memory() ->
    Cmd = "pid=`echo $$`;p=`ps -ef | awk -v pid=$pid '$2 == pid {print $3}'`;mem=`ps -o vsz -p $p | grep -v VSZ`;r=$(($mem/1024));echo $r",
    Result = os:cmd(Cmd),
    string:substr(Result, 1, length(Result) - 1).

+得到top命令獲得的虛擬內存消耗server

```erlang
get_top_virtual_memory() ->
    Cmd = "pid=`echo $$`;p=`ps -ef | awk -v pid=$pid '$2 == pid {print $3}'`;mem=`cat /proc/$p/stat | awk '{print $24}'`;r=$(($mem*4096/1024/1024));echo $r",
    Result = os:cmd(Cmd),
    case length(Result) > 1 of
        true ->
            string:substr(Result, 1, length(Result) - 1);
        false ->
            0
    end.
```

得到erlang運行時的進程信息

process_infos() ->          
    filelib:ensure_dir("./log/"),
    File = "./log/processes_infos.log",
    {ok, Fd} = file:open(File, [write, raw, binary, append]), 
    Fun = fun(Pi) ->
                   Info = io_lib:format("=>~p \n\n",[Pi]),
                  case  filelib:is_file(File) of
                        true   ->   file:write(Fd, Info);
                        false  ->
                            file:close(Fd),
                            {ok, NewFd} = file:open(File, [write, raw, binary, append]),
                            file:write(NewFd, Info)
                     end,
                     timer:sleep(20)
                 end,
    [Fun(erlang:process_info(P)) ||   P <- erlang:processes()].