Child dying after first line of code

[Xandux]

Hi there!

I'm writing a little program that needs to fork 2 times and then the child has to run some code. It should be quite an easy task, but my child seems to die right after the first line of code it runs..

int j = 0;
        for (j = 0; j < nrOfClients; j++) // let's assume nrOfClients = 2
	{
		int iPid = fork();

		switch ( iPid ) {
			case 0 :
					clientTCP();
			case -1:
				perror("Error while forking");
				exit(1);
			//default:
				//printf("Child %d created \n", j);
			}
	}
	sleep(30000);

void clientTCP(void)
{
	printf("prints this \n");
	int sock;
	if ((sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1)
	{
		printf("but doesn't come here");
		perror("Error creating socket");
		exit(1);
	}

	printf("or here.");
	int k;
	for (k = 0; k < nrOfRequests; k++)
	{
		char messageReceived[nrOfBytes];
		write(sock, messageOut, nrOfBytes);

		printf("clientTCP 2");
		int bytesReceived;
		bzero(&messageReceived, sizeof(messageReceived));
		if ((bytesReceived = read(sock, messageReceived, nrOfBytes)) == 0)
		{
			fprintf(stderr, "The server has terminated the connection. \n");
			close(sock);
			exit(0);
		}

		printf("clientTCP 3");
		printf("Child %d received %d bytes \n", getpid(), bytesReceived);
	}

It's probably a stupid mistake, but I'd appreciate it if someone can help me get further.

[MK27]

If that first bit of code is in main(), main() has nothing to do after the fork and so exits. When main exits, the parent process is done (altho the child will still be running).

You need to use waitpid() to wait for the child to exit.

	int i;
	pid_t pid = fork();

	if (!pid) {
		for (i=0;i<10;i++) {
			puts("hello world");
			sleep(1);
		}
                return 0;
	} else waitpid(pid);

	puts("done");

Try it with and without the else clause.

[Xandux]

Ah oops, There's a sleep(30000) beneath it atm.. so child's should have more than enough time. After some more testing I did the following:
- Removed all code from clientcp except for the sock and printf's.

Now I found out that the child actually goes into all the cases on the fork.. So it does case 0, then case -1 and even case default when i uncomment it..
How can a child do this?

(edited main post to show the sleep(30000))

[Xandux]

Damn, I totally forgot the connect() call after the socket() call. Apparently the program won't run unless there is a connect before a write. Makes sense, but the way the program reacts to it just doesn't..

The problem with the child going into all cases after the fork was an easy fix too, I had to exit the child after the childTCP was done..

Everything fixed now, thanks for the reply .

[EVOEx]

Damn, I totally forgot the connect() call after the socket() call. Apparently the program won't run unless there is a connect before a write. Makes sense, but the way the program reacts to it just doesn't..

The problem with the child going into all cases after the fork was an easy fix too, I had to exit the child after the childTCP was done..

Everything fixed now, thanks for the reply .

From the write() manual, at errors:

EPIPE fd is connected to a pipe or socket whose reading end is closed.
When this happens the writing process will also receive a SIG‐
PIPE signal. (Thus, the write return value is seen only if the
program catches, blocks or ignores this signal.)

So I expect your child receives a SIGPIPE signal, of which the default action is to kill the process. If you would have handled this signal, everything would have worked as expected.