pipe

XiaoMei · 11-22-2011, 04:39 AM

Hi,everyone, can somebody help me to solve the problem?
i be requested to sent out two ways pipe, and the signal is sending through the pipe, so what can i do?? HERE is my current coding:-

Code:

#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <stdlib.h>

#define MSGSIZE 100

char *msg1 = "tmn3013 SystemProgramming#1";
char *msg2 = "tmn3013 SystemProgramming#2";
char *msg3 = "tmn3013 SystemProgramming#3";


void sig_usr(int signo)
{
	if(signo == SIGINT)
	printf("Signal caught!");
	return;
}

int main(void)
{
	char inbuf[MSGSIZE];
	int p[2], i;
	pid_t pid,ppid;
	ppid = getpid();
	

	if((pid = fork()) == 0)
	{ //Child
		kill(ppid, SIGINT);
	}
	else{
		printf("%d %d ",ppid, pid);
		struct sigaction sig;
		sigemptyset(&sig.sa_mask);
		sig.sa_flags = 0;
		sig.sa_handler = sig_usr;
		if(sigaction(SIGINT,&sig,NULL) == 0)
		printf("Signal processed OKay ");
		sleep(10);
	}
	if(pipe(p) == -1)
	{
		perror("pipe call");
		exit(1);
	}
	
	switch(pid=fork())
	{
	case -1:
		perror("fork call");
		exit(2);
	case 0:
		close(p[0]);
		write(p[1], msg1, MSGSIZE);
		write(p[1], msg2, MSGSIZE);
		write(p[1], msg3, MSGSIZE);
		break;
	default:
		close(p[1]);
		for(i=0; i<3; i++)
		{
			read(p[0], inbuf, MSGSIZE);
			printf("%s\n", inbuf);
		}
		wait(NULL);
	}
	exit(0);
}

smallpond · 11-22-2011, 05:42 PM

Your message appears to have been cut off. You were just about to say what you expect the code to do and what it actually does and what you heave done to debug the problem.

XiaoMei · 11-22-2011, 09:41 PM

thanks for reply, but i not really understand what you trying to say. can has more declaration??? thanks

XiaoMei · 11-23-2011, 02:11 AM

i wish can send the signal through pipe

smallpond · 11-23-2011, 05:25 PM

Quote:

Originally Posted by XiaoMei

i wish can send the signal through pipe

signals are sent to processes. pipes are I/O devices.

XiaoMei · 11-24-2011, 11:16 PM

how about if i convert the signal to number, and pass the number through the pipe, is that logic????

Ramurd · 11-25-2011, 03:52 AM

Upon receiving a signal, you can send a message through the pipe (you could do that in a signal handler); upon which the process on the other end acts:
As smallpond said: signals are sent to processes. A pipe is not a process, and as such, you cannot send a signal through a pipe... try to visualize it ;-)

But the sender can send a message which the listener has to interpret, so it acts like you wanted.
In pseudo code:

sender:

Code:

catch signal(SIGTERM)
{
   send_message("terminate");
}

listener:

Code:

receive_message(string)
{
   if(string == "terminate")
   {
       exit;
   }
   else
   {
       print(string);
   }
}

get the idea?

XiaoMei · 11-25-2011, 10:05 PM

thank you, Ramurd, when i see it, i almost cry le, thank you so much!!!

XiaoMei · 11-25-2011, 10:21 PM

Ramurd, i try it, but it doesn't work....since now i dealing with parent and child process...the scenario likes this, a pipe will be establish between the parent and child, and the signal should be able to send through the pipe from parent and child...

Ramurd · 11-26-2011, 02:42 AM

well; it's not that hard. If it's a real parent/child process, so the child is forked off the parent, you could use IPC calls as well...
You might want to read up on signals: what happens if a signal gets sent to the parent, what signal does the child get? Just remember: a pipe is an I/O stream, and you cannot send signals to that... you'll have to write a signal handler if what you want to happen on a certain signal is different from the default.

What process are you trying to send and catch? What code do you have?

XiaoMei · 11-26-2011, 07:44 PM

Raymurd, thanks for ur patient, the above one is my code, sending kill signal from parent to child, and from child to parent