++操作与lists:concat操作比较 （lists:concat运算结果）

测试环境

Linux jason-lxw 3.2.0-39-generic #62-Ubuntu SMP Thu Feb 28 00:28:53 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

4G内存

Erlang R14B04 (erts-5.8.5) [source] [64-bit] [smp:4:4] [rq:4] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8.5  (abort with ^G)

1> 

测试数据：

add()->

    III="langxw",

    MMM= 10,

    OFFFFF = 100,

    "display uuuuuuuuu, ffstate ,"      ++                

                        " uuusername, uubio, "++          

                        " uuavatar_url," ++               

                        " uusex todo langgfriendship f , langgusers u where fffolllleriii=uuuuuuuuu " ++                                                                                                                                                                                     

                        " aaa | fffollllediii = '", III, "')" ++

                        " aaa Lype='1'" ++                

                        " rrrr by ffctttte_datt ssss lllll " ++ integer_to_list(MMM) ++" FFeeee " ++ integer_to_list(OFFFFF) ++";".                                                                                                                                                          

 

 

concat()->

    III="langxw",

    MMM= 10,

    OFFFFF = 100,

    Sql = lists:concat(["display uuuuuuuuu, ffstate ,"     

                        " uuusername, uubio, ",           

                        " uuavatar_url,",                                                                                                                                                                                                                                                     

                              

                        " uusex todo langgfriendship f , langgusers u where fffolllleriii=uuuuuuuuu ",                                                                                                                                                                                       

                        " aaa | fffollllediii = '", III, "')",

                        " aaa Type='1'",                  

                        " rrrr by ffctttte_datt ssss lllll ", MMM," FFeeee ", OFFFFF,";"                                                                                                                                                                                                     

                        ]).

 

lists:concat操作结果

49> test_lists_concat:start(1,10000).  ：参数：第一个参数是单进程，第二个参数是  add/concat执行次数

===============================================================

process #1 send 10000 request spent 62 ms

total spent=62 ms,avg spent=62 ms

=====================================================================

true

50> test_lists_concat:start(1,100000).

===============================================================

process #1 send 100000 request spent 554 ms

total spent=554 ms,avg spent=554 ms

=====================================================================

true

51> test_lists_concat:start(1,100 0000).

===============================================================

process #1 send 1000000 request spent 5699 ms

total spent=5699 ms,avg spent=5699 ms

=====================================================================

true

 

++操作结果

54> test_lists_concat:start(1,10000). 

===============================================================

process #1 send 10000 request spent 2 ms

total spent=2 ms,avg spent=2 ms

=====================================================================

true

55> test_lists_concat:start(1,100000).

===============================================================

process #1 send 100000 request spent 27 ms

total spent=27 ms,avg spent=27 ms

=====================================================================

true

56> test_lists_concat:start(1,100 0000).

===============================================================

process #1 send 1000000 request spent 206 ms

total spent=206 ms,avg spent=206 ms

=====================================================================

true

57> test_lists_concat:start(1,10000000).

===============================================================

process #1 send 10000000 request spent 5257 ms

total spent=5257 ms,avg spent=5257 ms

=====================================================================

 

结论：（仅代表当前测试总结学习）乍看lists:concat源码，以为lists:concat执行效率会比++操作快，但实际测试结果，lists:concat远不如++操作。这可能因为lists:concat里面的递归（非尾递归）造成的。从上面测试数据可以看出lists:concat 比++操作要慢几十倍。

 

 

 

 

 

-module(test_lists_concat).

-export([test/2]).

       


-export([start/2,dotest/3]).  
  
start(Processes,Loops)->  
    ets:new(ib,[named_table,set]),     
    [spawn(?MODULE,dotest,[self(),X,Loops])||X<-lists:seq(1,Processes)],  
    recv(Processes,Loops),  
    ets:delete(ib).  
  
recv(Processes,Loops)->  
    receive  
        {fin,ProcessNum,Elapse}->          
            ets:insert(ib,{ProcessNum,Elapse}),  
            case ets:info(ib,size) of          
                Processes->  
                    %%got all the resp                 
                    print_result(Processes,Loops);     
                _->  
                    recv(Processes,Loops)              
            end;  
        Err->  
            io:format("recv unknowen msg~n"),  
            recv(Processes,Loops)              
    end.  
  
print_result(Processes,Loops)->  
    io:format("===============================================================~n"),  
    TotalElapse=  
    lists:foldr(  
     fun({ProcessNum,Elapse},Acc)->     
        io:format("process #~p send ~p request spent ~p ms~n",[ProcessNum,Loops,Elapse]),         
        Acc + Elapse  
     end,      
     0,  
     ets:tab2list(ib)  
    ),  
    AvgElapse=TotalElapse div Processes,  
    io:format("total spent=~p ms,avg spent=~p ms~n",[TotalElapse,AvgElapse]),  
    io:format("=====================================================================~n").  
      
dotest(From,ProcessNum,Loops)->  
    Start=timestamp_in_millinsec(),    
    [lists_concat()||X<-lists:seq(1,Loops)],  
    Elapse=timestamp_in_millinsec()-Start,  
    From!{fin,ProcessNum,Elapse}.      
      
timestamp_in_millinsec()->                                                                                                                                                                                                                                                                                                  
    {MegaSec,Sec,MicoSec}=erlang:now(),  
    MegaSec * 1000000000+Sec*1000+MicoSec div 1000.  

lists_concat() ->
    %%lists:concat(["langxw", "langxw", "langxw"]),
    %%""++"langxw"++"langxw",
    %%concat(),
    add(),
    ok.

add()->
    III="langxw",
    MMM= 10,
    OFFFFF = 100,
    "display uuuuuuuuu, ffstate ,"      ++
                        " uuusername, uubio, "++
                        " uuavatar_url," ++
                        " uusex todo langgfriendship f , langgusers u where fffolllleriii=uuuuuuuuu " ++
                        " aaa | fffollllediii = '", III, "')" ++
                        " aaa Lype='1'" ++
                        " rrrr by ffctttte_datt ssss lllll " ++ integer_to_list(MMM) ++" FFeeee " ++ integer_to_list(OFFFFF) ++";".


concat()->
    III="langxw",
    MMM= 10,
    OFFFFF = 100,
    Sql = lists:concat(["display uuuuuuuuu, ffstate ,"
                        " uuusername, uubio, ",
                        " uuavatar_url,",
                        " uusex todo langgfriendship f , langgusers u where fffolllleriii=uuuuuuuuu ",
                        " aaa | fffollllediii = '", III, "')",
                        " aaa Type='1'",
                        " rrrr by ffctttte_datt ssss lllll ", MMM," FFeeee ", OFFFFF,";"
                        ]).


test(Pro, Num)->
o.

 

 

补充：

51> test_lists_concat:start(1,100 0000).

===============================================================

process #1 send 1000000 request spent 5699 ms

total spent=5699 ms,avg spent=5699 ms

 

56> test_lists_concat:start(1,100 0000).

===============================================================

process #1 send 1000000 request spent 206 ms

@石头哥哥 这两次结果比较 ++ 比lists:concat快了大约27倍。

 

@erlang-菜鸟

个人理解（没测试）假设有两个list分别是A和B

1、如果A的长度远远大约B的长度时。A++B操作 会比 B++A慢

 

2、如果1成立，同样假设有A1，A2，A3，A4...An

   如果A1长度>A2长短>A3长度>A4长度>...>An长度，

   A1++A2++A3++A4++...++An 会比

   {A4++..++An :记为R

    A3++R :记为R

    A2++R :记为R

    A1++R 

    }慢。

基于这样的理解，简单的误认为lists:concat和++的快慢显示是错误的。还有就是lists:concat里面调用了非尾递归。感兴趣的同学继续测试一下。

找时间测试研究一下++操作顺序