Simultaneous processes

This is a discussion on Simultaneous processes within the C Programming forums, part of the General Programming Boards category; I have done a small amount of programming using fork() to create a child process. I want to have a ...

  1. #1
    Prying open my third eye.
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    Simultaneous processes

    I have done a small amount of programming using fork() to create a child process. I want to have a client/server pair to be able to send message string back and forth simulataneously so that while one is typing in a message, a message can be receieved from the other and printed. I supposed I could use fork but is there a better way to do this?

    To make it a little more clear:

    Say a user is typing in a message, at the same time a message comes over the line. I want to be able to print that message to the screen WHILE the user is still typing in a message.

    Any help is appreciated.

    Thanks
    "So you're one of those condescending UNIX computer users?"

    "Here's a nickel, kid. Get yourself a better computer."

  2. #2
    Registered User mitakeet's Avatar
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    You should explore select() and see if that does what you need.

    Free code: http://sol-biotech.com/code/.

    It is not that old programmers are any smarter or code better, it is just that they have made the same stupid mistake so many times that it is second nature to fix it.
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  3. #3
    Prying open my third eye.
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    I'll try it.

    I've done some minor code using select, so I am not sure if it will read the socket while a user is inputting a string to send.

    Thanks
    "So you're one of those condescending UNIX computer users?"

    "Here's a nickel, kid. Get yourself a better computer."

  4. #4
    Registered User mitakeet's Avatar
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    I am pretty sure on *nix you can mix and match sockets and file descriptors.

    Free code: http://sol-biotech.com/code/.

    It is not that old programmers are any smarter or code better, it is just that they have made the same stupid mistake so many times that it is second nature to fix it.
    --Me, I just made it up

    The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man.
    --George Bernard Shaw

  5. #5
    #include<xErath.h> xErath's Avatar
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    select?? that's for sockets... bleh

    Use a fifo !
    something simple like
    Code:
    #include <unistd.h>
    #include <fcntl.h>
    #include <sys/stat.h>
    
    #define FIFO_NAME "/tmp/tha_fifo_stuff"
    
    int main(){
    	int cpid, fd;
    	char msg[1000] = "";
    	mkfifo(FIFO_NAME,S_IRWXU);
    
    	switch(cpid = fork()){
    	case -1:perror("fork()");
    		return 0;
    	case 0: //child
    		fd = open(FIFO_NAME,O_WRONLY|O_NONBLOCK);
    		strcpy(msg,"hello daddy");
    		write(fd,msg,strlen(msg)+1);
    		close(fd);
    		return 0;
    	default:
    		wait(&cpid);
    		fd = open(FIFO_NAME,O_RDONLY);
    		read(fd,msg,999);
    		printf("my son with pid %d sayd: '%s'\n",cpid,msg);
    		close(fd);
    	}
    	unlink(FIFO_NAME);
    	return 0;
    }

  6. #6
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    Quote Originally Posted by xErath
    select?? that's for sockets... bleh

    Use a fifo !
    something simple like
    Code:
    #include <unistd.h>
    #include <fcntl.h>
    #include <sys/stat.h>
    
    #define FIFO_NAME "/tmp/tha_fifo_stuff"
    
    int main(){
    	int cpid, fd;
    	char msg[1000] = "";
    	mkfifo(FIFO_NAME,S_IRWXU);
    
    	switch(cpid = fork()){
    	case -1:perror("fork()");
    		return 0;
    	case 0: //child
    		fd = open(FIFO_NAME,O_WRONLY|O_NONBLOCK);
    		strcpy(msg,"hello daddy");
    		write(fd,msg,strlen(msg)+1);
    		close(fd);
    		return 0;
    	default:
    		wait(&cpid);
    		fd = open(FIFO_NAME,O_RDONLY);
    		read(fd,msg,999);
    		printf("my son with pid %d sayd: '%s'\n",cpid,msg);
    		close(fd);
    	}
    	unlink(FIFO_NAME);
    	return 0;
    }

    It didnt work for me. Parent kept waiting. Never received the message from "son". Here is the one that worked.

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    #include <string.h>
    #include <fcntl.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <unistd.h>
    
    #define FIFO_NAME "/tmp/tha_fifo_stuff"
    
    int main(){
    	int cpid, fd;
    	char msg[1000] = "";
    	pid_t chpid;
    
    	mkfifo(FIFO_NAME,S_IRWXU);
    
    	switch(cpid = fork()){
    	case -1:perror("fork()");
    		return 0;
    	case 0: //child
    		fd = open(FIFO_NAME,O_WRONLY);
    		if (fd<0)
    		{
    			perror("open");
    			exit(0);
    		}
    		strcpy(msg,"hello daddy");
    		write(fd,msg,strlen(msg)+1);
    		sleep(5);
    		close(fd);
    		exit(0);
    	default:
    		fd = open(FIFO_NAME,O_RDONLY);
    		read(fd,msg,999);
    		printf("my child with pid %d sayd: '%s'\n",cpid,msg);
    		wait(&chpid);
    		printf("my child has exited. My wait is over. bye!!!\n");
    		close(fd);
    	}
    	unlink(FIFO_NAME);
    	return 0;
    }
    My output.

    [root@linux-outside snoopy]# ./fifo1
    my child with pid 13124 sayd: 'hello daddy'
    my child has exited. My wait is over. bye!!!
    [root@linux-outside snoopy]#

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