【Erlang新手成长日记】Erlang端口与外部C程序交互

谁借莪１个温暖的怀抱￠ 2022-01-09 10:19 259阅读 0赞

参考文档：

《Programming Erlang》，第12章：Interfacing Techniques

创建C源文件：

hello.c  具体函数的实现

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][] hello.c

int twice(int arg) {
        return (arg * arg);
    }
    
    int sum(int arg1, int arg2) {
        return (arg1 + arg2);
    }

hello\_driver.c  驱动程序运行

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][] hello\_driver.c

#include <stdio.h>
    
    #define BUFFER_SIZE 100
    
    typedef unsigned char byte; //8 bit
    
    int read_cmd(byte *buffer);
    int write_cmd(byte *buffer, int length);
    
    int main() {
        int function_number; //函数号
        int arg1, arg2; //参数
        int result; //结果
        byte buffer[BUFFER_SIZE]; //缓冲区
        
        while(read_cmd(buffer) > 0) {
            function_number = buffer[0];
            switch(function_number) {
                case 1:
                    //执行函数 twice
                    arg1 = buffer[1];
                    result = twice(arg1);
                    break;
                case 2:
                    //执行函数 sum
                    arg1 = buffer[1];
                    arg2 = buffer[2];
                    result = sum(arg1, arg2);
                    break;
                default:
                    // error
                    break;
            }
            buffer[0] = result;
            write_cmd(buffer, 1);
        }
        
        return 0;
    }

erl\_communication.c  与Erlang程序交互

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][] erl\_communication.c

1 #include <unistd.h>
     2 
     3 typedef unsigned char byte;
     4 
     5 int read_cmd(byte *buffer);
     6 int write_cmd(byte *buffer, int length);
     7 int read_exact(byte *buffer, int length);
     8 int read_exact(byte *buffer, int length);
     9 
    10 int read_cmd(byte *buffer) {
    11     int length; //int 长度 16 bit
    12     
    13     if(read_exact(buffer, 2) != 2) {
    14         return -1;
    15     }
    16     length = (buffer[0] << 8) | buffer[1];
    17     
    18     return read_exact(buffer, length);
    19 }
    20 
    21 int write_cmd(byte *buffer, int length) {
    22     byte li; //unsigned char 长度 8 bit
    23     
    24     li = (length >> 8) & 0xff;
    25     write_exact(&li, 1);
    26     li = length & 0xff;
    27     write_exact(&li, 1);
    28     
    29     return write_exact(buffer, length);
    30 }
    31 
    32 int read_exact(byte *buffer, int length) {
    33     int i, got = 0;
    34     
    35     do {
    36         /*
    37          * read函数定义：ssize_t read(int fildes, void *buf, size_t nbyte);
    38          * read函数描述：The read() function attempts to read nbyte bytes from the file associated with the open file descriptor, fildes, into the buffer pointed to by buf.
    39          * 备注：fildes值0，标准输入
    40          */
    41         if((i = read(0, (buffer + got), (length - got))) <= 0) {
    42             return i;
    43         }
    44         got += i;
    45     } while(got < length);
    46     
    47     return length;
    48 }
    49 
    50 int write_exact(byte *buffer, int length) {
    51     int i, wrote = 0;
    52     
    53     do {
    54         /*
    55          * write函数定义：ssize_t write(int fildes, const void *buf, size_t nbyte);
    56          * write函数描述：The write() function attempts to write nbyte bytes from the buffer pointed to by buf to the file associated with the open file descriptor, fildes.
    57          * 备注：fildes值1，标准输出
    58          */
    59         if((i = write(1, (buffer + wrote), (length - wrote)))) {
    60             return i;
    61         }
    62         wrote += i;
    63     } while(wrote < length);
    64     
    65     return length;
    66 }

创建Erlang源文件

hello.erl  创建进程，打开与C生成的可执行文件之间的端口，通过消息传递进行交互

Port = open\_port(PortName, PortSettings)

open\_port/2：[http://www.erlang.org/doc/man/erlang.html\#open\_port-2][http_www.erlang.org_doc_man_erlang.html_open_port-2]

This returns a port. The following messages can be sent to a port:

Port ! \{PidC, \{command, Data\}\}

Send Data (an IO List) to the port.

Port ！\{PidC, \{connect, Pid1\}\}

Change the PID of the connected process from PidC to Pid1.

Port ! \{PidC, close\}

Close the port.

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][] hello.erl

1 -module(hello).
     2 
     3 -export([start/0, stop/0]).
     4 -export([twice/1, sum/2]).
     5 
     6 -define(PORTNAME, ?MODULE).
     7 
     8 start() ->
     9     Fun = fun() ->
    10             register(?PORTNAME, self()),
    11             process_flag(trap_exit, true),
    12             Port = open_port({spawn, "./hello"}, [{packet, 2}]),
    13             loop(Port)
    14         end,
    15     spawn(Fun).
    16     
    17 stop() -> 
    18     ?PORTNAME ! stop.
    19     
    20 twice(X) -> call_port({twice, X}).
    21 sum(X, Y) -> call_port({sum, X, Y}).
    22 
    23 call_port(Message) ->
    24     ?PORTNAME ! {call, self(), Message},
    25     receive
    26         {?PORTNAME, Result} ->
    27             Result
    28     end.
    29     
    30 loop(Port) -> 
    31     receive
    32         {call, Caller, Message} ->
    33             Port ! {self(), {command, encode(Message)}},
    34             receive
    35                 {Port, {data, Data}} ->
    36                     Caller ! {?PORTNAME, decode(Data)}
    37             end,
    38             loop(Port);
    39         stop ->
    40             Port ! {self(), close},
    41             receive
    42                 {Port, closed} ->
    43                     exit(normal)
    44             end;
    45         {'EXIT', Port, Reason} ->
    46             exit({port_terminated, Reason})
    47     end.
    48     
    49 encode({twice, X}) ->
    50     [1, X];
    51 encode({sum, X, Y}) ->
    52     [2, X, Y].
    53     
    54 decode([Int]) ->
    55     Int.

编译C源文件，生成可执行文件

gcc -o hello hello.c hello_driver.c erl_communication.c

编译Erlang源文件，生成.beam文件

erlc hello.erl

转载于:https://www.cnblogs.com/dyingbleed/archive/2012/09/01/2666698.html

[ContractedBlock.gif]: https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif
[ExpandedBlockStart.gif]: /images/20220109/69860fed883a41948988b45d527909dd.png
[http_www.erlang.org_doc_man_erlang.html_open_port-2]: http://www.erlang.org/doc/man/erlang.html#open_port-2