執行進程通信

我剛剛開始閱讀Erlang編程書。有一個非常單一的例子，只是文件。執行進程通信

如果我執行：

> c(afile_server). 
> c(afile_client). 
> Server = afile_server:start("."). 
> client:get_file(Server, "file1"). 
> client:get_file(Server, "file2"). 
> client:get_file(Server, "file3").

一切正常，只是文件。顯示三個文件內容。

但是，如果我做的：

> c(afile_server). 
> Server = afile_server:start("."). 
> Server ! { self(), { get_file, "file1" } }. 
> receive 
    { Server, Content } 
     Content 
    end.

它只是文件。但是，如果我更改了我想要讀取的文件（在第一次調用之後），例如

> Server ! { self(), { get_file, "file2" } }. 
> receive 
    { Server, Content } 
     Content 
    end.

接收塊並沒有返回。你們可以幫忙嗎？我想，這是一個非常愚蠢的錯誤！此致敬禮。

文件：

服務器：

-module(afile_server). 
-export([start/1, loop/1]). 

start(Dir) -> spawn(afile_server, loop, [Dir]). 

loop(Dir) -> 
    receive 
    {Client, list_dir} -> 
     Client ! {self(), file:list_dir(Dir)}; 
    {Client, {get_file, File}} -> 
     Full = filename:join(Dir, File), 
     Client ! {self(), file:read_file(Full)} 
    end, 
    loop(Dir).

客戶

%% --- 
%% Excerpted from "Programming Erlang, Second Edition", 
%% published by The Pragmatic Bookshelf. 
%% Copyrights apply to this code. It may not be used to create training material, 
%% courses, books, articles, and the like. Contact us if you are in doubt. 
%% We make no guarantees that this code is fit for any purpose. 
%% Visit http://www.pragmaticprogrammer.com/titles/jaerlang2 for more book information. 
%%--- 
-module(afile_client). 
-export([ls/1, get_file/2]). 

ls(Server) -> 
    Server ! {self(), list_dir}, 
    receive 
    {Server, FileList} -> 
     FileList 
    end. 

get_file(Server, File) -> 
    Server ! {self(), {get_file, File}}, 
    receive 
    {Server, Content} -> 
     Content 
    end.

來源

2016-09-29 Nadilson Ferreira

那是因爲你在shell中運行這和重用名稱Contentreceive模式，並且這兩個文件可能在您的文件系統中具有不同的內容，因此receive會阻止該進程獲取具有相同內容的消息。要解決此問題，您可以每次使用Content的不同名稱，或者使用f(Content)明確「忘記」該變量。

1> c(afile_server). 
{ok,afile_server} 
2> Server = afile_server:start("."). 
<0.64.0> 
3> Server ! { self(), { get_file, "file1" } }. 
{<0.57.0>,{get_file,"file1"}} 
4> receive {Server, Content} -> Content end. 
{ok,<<"file1\n">>} 
5> Server ! { self(), { get_file, "file2" } }. 
{<0.57.0>,{get_file,"file2"}} 
6> receive {Server, Content} -> Content after 1000 -> timeout end. 
timeout 
7> receive {Server, Content2} -> Content2 end. 
{ok,<<"file2\n">>} 
8> Server ! { self(), { get_file, "file3" } }. 
{<0.57.0>,{get_file,"file3"}} 
9> receive {Server, Content} -> Content after 1000 -> timeout end. 
timeout 
10> f(Content). 
ok 
11> receive {Server, Content} -> Content after 1000 -> timeout end. 
{ok,<<"file3\n">>}

來源

2016-09-29 05:05:16 Dogbert

執行進程通信

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