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13-09-2019 - |
题
我很新的Erlang和我目前正在读乔·阿姆斯特朗的书,第一章“并发编程”。我试图运行的进程的列表来计算,如果一个数是素(天真的方法)。但我的代码运行,就好像没有过程。这两种方法都具有相同的持续时间。我在哪里错了?
shell.erl:
c(prime).
%a list of primes
NUMS=[102950143,102950143,102950143,102950143,102950143].
%time start
NOW1=now().
io:fwrite("Monothread~n").
%for each number test if it is a prime
lists:foreach( fun(N)->
RESULT=prime:is_prime(N),
io:fwrite("Result N=~p ~n",[RESULT])
end, NUMS).
%display the duration
io:fwrite("Duration N=~p ~n",[timer:now_diff(now(),NOW1)/1.0e6]).
%time start
NOW2=now().
io:fwrite("Multithread~n").
%for each number, spawn a new process and test if it is a prime
lists:foreach( fun(N)->ProcId = prime:start(),
io:fwrite("Calculating : procId=~p N=~p ~n",[ProcId,N]),
RESULT=prime:is_prime(ProcId,N),
io:fwrite("Result N=~p ~n",[RESULT])
end, NUMS).
%display the duration
io:fwrite("Duration N=~p ~n",[timer:now_diff(now(),NOW2)/1.0e6]).
halt().
文件prime.erl:
-module(prime).
-export([start/0,is_prime/1,is_prime/2]).
%run the forever_function
start()->spawn(fun forever_function/0).
%catch the queries
forever_function()->
receive
{ From,Number} -> From! is_prime(self(),2,Number),
forever_function()
end.
%monothreaded function
is_prime(Number)->is_prime(self(),2,Number).
%multithreaded function
is_prime(ProcessID,Number)->
ProcessID ! {self(),Number},
receive
RESULT->RESULT
end.
%recursive function scanning all the numbers from 2 to Number
is_prime(ProcessID,Div,Number)->
if
Div =:= Number -> {{number,Number},{prime,true}};
Number rem Div =:= 0 -> {{number,Number},{prime,false}};
true-> is_prime(ProcessID,Div+1,Number)
end.
谢谢,
皮尔
解决方案
在你的清单:在第二块的foreach调用,你在呼唤RESULT=prime:is_prime(ProcId,N)
,这是做的结果receive
。所以,你产卵一个过程,然后等待它完成,直到你产卵下一道工序。这就是为什么它花费的时间是相同的量单线程方式:两种方式,你只能做一次一个
相反,你需要首先产卵所有进程(使用类似lists:map
让所有的PID的轨道),然后等待在单独的步骤的结果。需要注意的是意味着你必须拆分ProcessID ! {self(),Number}
部分从receive
一部分,这样可以在第一步骤中完成,否则你只是在产卵一堆空闲进程。
所以,是这样的:
Pids = lists:map( fun(N)-> ProcId = prime:start(N),
io:fwrite("Calculating : procId=~p N=~p ~n",[ProcId,N]),
ProcId end, NUMS).
lists:foreach( fun(ProcId) -> {N,RESULT}=prime:is_prime(ProcId),
io:fwrite("Result procId=~p N=~p Result=~p ~n", [ProcId,N,RESULT]) end, Pids).
start(N)->spawn(?MODULE, forever_function, [N]).
forever_function(Number)->
Result = is_prime(self(),2,Number),
receive
{ From, get_result } -> From! {Number,Result},
% unnecessary since we never call this Pid again, but do it anyway :)
forever_function()
% could also add more cases here to set the number
% or even do a one-shot function like before
end.
%multithreaded function
is_prime(ProcessID)->
ProcessID ! {self(),get_result},
receive
RESULT->RESULT
end.
注意:这是未经测试,因此它可能需要一些调整
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