Process API Programming

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

int main(void)
{
    printf("My pid = %d. My parent's pid = %d\n", getpid(), getppid());
    return 0;
}

$ gcc -o showpid showpid.c -Wall
$ ./showpid
My pid = 854. My parent's pid = 381
$ ./showpid
My pid = 855. My parent's pid = 381
$ ./showpid
My pid = 856. My parent's pid = 381
$ ./showpid
My pid = 857. My parent's pid = 381
$ ps x
...
 381 p2 S 0:01 -sh (csh)
...
$ 

// simpfork.c
#include <stdio.h>
#include <unistd.h>
main()
{
    int i;
    printf("simpfork: pid = %d\n", getpid());
    i = fork();
    printf("Did a fork. It returned %d. getpid = %d. getppid = %d\n",
        i, getpid(), getppid());
}

$ gcc -o simpfork simpfork.c -Wall
$ ./simpfork
simpfork: pid = 914
Did a fork. It returned 915. getpid = 914. getppid = 381
Did a fork. It returned 0. getpid = 915. getppid = 914

$ ./simpfork
simpfork: pid = 928
Did a fork. It returned 0. getpid = 929. getppid = 928
Did a fork. It returned 929. getpid = 928. getppid = 381 

// simpfork2.c
#include <stdio.h>
#include <unistd.h>
main()
{
        int i;
        i = fork();
        if (i == 0) {
                printf("Child. getpid() = %d, getppid() = %d\n", getpid(), getppid());
                sleep(5);
                printf("After sleeping. getpid() = %d, getppid() = %d\n",
                        getpid(), getppid());
        } else {
                printf("Parent exiting early...\n");
        }
}

$ gcc -o simpfork2 simpfork2.c -Wall 
$ ./simpfork2
Child. getpid() = 1301, getppid() = 1300
Parent exiting now
After sleeping. getpid() = 1301, getppid() = 1

// simpfork3.c
#include <stdio.h>
#include <unistd.h>

int K;

main()
{
    int i;
    int j;
    j = 200;
    K = 300;
    printf("Before forking: j = %d, K = %d ", j, K);
    i = fork();

    if (i > 0) { /* Delay the parent */
        sleep(1);
        printf("After forking, parent: j = %d, K = %d\n", j, K);
    } else {
    j++;
    K++;
    printf("After forking, child: j = %d, K = %d\n", j, K);
    }
}

$ gcc -o simpfork3 simpfork3.c -Wall
$ ./simpfork3
Before forking: j = 200, K = 300
After forking, child: j = 201, K = 301
After forking, parent: j = 200, K = 300

$ simpfork3 > output
$ cat output
Before forking: j = 200, K = 300
After forking, child: j = 201, K = 301
Before forking: j = 200, K = 300
After forking, parent: j = 200, K = 300

// simpfork4.c
#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <unistd.h>

main() {
	int i;
	int seekp;
	int fd;
	char *s1;
	char s2[1000];

	fd = open("tmpfile", O_WRONLY | O_TRUNC | O_CREAT, 0666);

	s1 = "Before forking\n";
	write(fd, s1, strlen(s1));

	i = fork();

	if (i > 0) {
		sleep(1); /* Delay the parent by one second */
		s1 = "Parent";
	} else {
		s1 = "Child";
	}

	seekp = lseek(fd, 0, SEEK_CUR);
	sprintf(s2, "%s: After forking: Seek pointer = %d\n", s1, seekp);
	write(fd, s2, strlen(s2));
}

$ gcc -o simpfork4 simpfork4.c -Wall 
$ ./simpfork4
$ cat tmpfile
Before forking
Child: After forking: Seek pointer = 15
Parent: After forking: Seek pointer = 55

// simpfork5.c
#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>

int main() {

	pid_t pid1, pid2, pid3, pid4;
	printf("Parent[A] of all: %d\n", getpid());

	pid1 = fork();

	if (pid1 == 0) {   // Child Process, lets say B.
		printf("Child[B] with id: %d and its Parent id: %d \n", getpid(),
				getppid());
		pid2 = fork();
		if (pid2 == 0) { // Child process, lets say D.
			printf("Child[D] with id: %d and its Parent id: %d \n", getpid(),
					getppid());
		}
	}
	if (pid1 > 0) {
		pid3 = fork();
		if (pid3 == 0) { // Child process, lets say C.
			printf("Child[C] with id: %d and its Parent id: %d \n", getpid(),
					getppid());
			pid4 = fork();
			if (pid4 == 0) { // Child process, lets say E.
				printf("Child[E] with id: %d and its Parent id: %d \n",
						getpid(), getppid());
			}

		}
	}
	for (int i = 0; i < 3; i++)
		wait(NULL);
}

$ gcc -o simpfork5 simpfork5.c -Wall 
$ ./simpfork5
Parent[A] of all: 27385
Child[B] with id: 27386 and its Parent id: 27385
Child[C] with id: 27387 and its Parent id: 27385
Child[D] with id: 27388 and its Parent id: 27386
Child[E] with id: 27389 and its Parent id: 27387

// simpfork6.c
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>

int main(int argc, char *argv[]) {
	int pid;
	/* fork another process */
	pid = fork();
	if (pid < 0) { /* error occurred */
		fprintf(stderr, "Fork Failed\n");
		exit(-1);
	} else if (pid == 0) { /* child process */
		execlp("/bin/ls", "ls", NULL);
	} else { /* parent process */
		/* parent will wait for the child to complete */
		wait(NULL);

		printf("Child Complete -- parent now exiting.\n");
		exit(0);
	}
	return 0;
}

$ gcc -o simpfork6 simpfork6.c -Wall 
$ ./simpfork6
simpfork6 simpfork6.c
Child Complete -- parent now exiting.

// simpfork7.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

void main() {
	int n, m, status;

	n = fork();
	if (n == -1)
		exit(1);
	else {
		if (n != 0) /* Parent Process */
		{
			printf("-p--  value of fork %d  PID = %d \n", n, getpid());
			printf("-p--  Parent PID = %d \n", getppid());
			m = wait(&status);
			printf("-p--  first exit status = %d \n", status);
			status = status >> 8;
			printf("-p--  exit status of child process = %d\n", status);
			printf("-p--  child PID that just stop = %d\n", m);
			fflush(stdout);
			m = execl("com", "com", NULL);
			printf(" Return to parent process ** ,m=%d \n", m);
			exit(0);

		} else {
			printf("\n");
			printf("\n");
			printf("-c--  value of fork = %d \n", n);
			printf("-c--  this PID = %d and Parent PID = %d\n "\
, getpid(),
					getppid());
			sleep(4);
			fflush(stdout);
			m = execl("com", "com", NULL);
			exit(2);
		}
	}

}

$ gcc -o simpfork7 simpfork7.c -Wall 
$ ./simpfork7
-p--  value of fork 4463  PID = 4462 
-p--  Parent PID = 2646 
.
.
.
-c--  value of fork = 0 
-c--  this PID = 4463 and Parent PID = 4462
-p--  first exit status = 512 
-p--  exit status of child process = 2
-p--  child PID that just stop = 4463
 Return to parent process ** ,m=-1 

// simpshell.c
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

/* a simple define for convenience */
#define TRUE 1

int main() {
	/* C declaration before any function call */
	int pid, i = 0;
	char tab[256], *s;

	/* the main loop of our shell */
	while (TRUE) {
		/* the printf to print strings and numbers */
		printf("prompt %d> ", i);
		/* "flush" the standard output */
		fflush(stdout);

		/* read the command line */
		s = gets(tab);

		if (s == NULL) { /* <Control+D> pressed */
			fprintf(stderr, "Bye bye\n");
			exit(0);
		}

		/* one process running */
		pid = fork();
		/* 2 processes running */
		printf("I'm running\n");

		switch (pid) /* where are we ? */
		{
		case 0: /* in the child! */
			printf("In the child\n");
			/* exec command */
			execlp(tab, tab, NULL);
			/* executed only if the exec command fails */
			perror("exec");
			exit(0);
			break;
		case -1: /* in... the parent: fork has failed no wait!*/
			perror("fork");
			break;
		default: /* in the parent, the fork worked! */
			printf("In the parent.. wait\n");
			wait(0);
			i++; /* for the next command */
		}
	}
	/* end of the loop */

	return 0;
}

$ gcc -o simpshell simpshell.c -Wall 
$ ./simpshell
prompt 0> ls
I'm running
In the parent.. wait
I'm running
In the child
pipe1.c  pipe3.c    programA   signal   simpfork7    simpshell Other_Multi-Socket.zip chat_socket   simpshell.c  simpshell.cc 
5287 done
prompt 1> date
I'm running
In the parent.. wait
I'm running
In the child
Fri Sep 12 07:42:28 ICT 2014
5288 done
prompt 2> pwd
I'm running
In the parent.. wait
I'm running
In the child
/home/wiroon/os
5289 done

// simpshell.cc
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <iostream>

using namespace std;

/* a simple define for convenience */
#define TRUE 1

int main() {
	int pid, i = 0;
	char tab[1024];

	/* the main loop of our shell */
	while (TRUE) {
		/* print strings and numbers */
		cout << "prompt " << i << "> ";

		/* read the command line */
		cin >> tab;

		if (tab[0] == 0) { /* <Control+D> pressed */
			cerr << "Bye bye\n";
			exit(0);
		}

		/* one process running */
		pid = fork();
		/* 2 processes running */
		cout << "I'm running\n";

		switch (pid) /* where are we ? */
		{
		case 0: /* in the child! */
			cout << "In the child\n";
			/* exec command */
			execlp(tab, tab, NULL);
			/* executed only if the exec command fails */
			perror("exec");
			exit(0);
			break;
		case -1: /* in... the parent: fork has failed no wait!*/
			perror("fork");
			break;
		default: /* in the parent, the fork worked! */
			cout << "In the parent.. wait\n";
			cout << wait(0) << " done\n";
			i++; /* for the next command */
		}
	}
	/* end of the loop */

	return 0;
}

$ g++ -o simpshell simpshell.cc -Wall 
$ ./simpshell
prompt 0> ls
I'm running
In the parent.. wait
I'm running
In the child
pipe1.c  pipe3.c    programA   signal   simpfork7    simpshell Other_Multi-Socket.zip chat_socket   simpshell.c  simpshell.cc 
5287 done
prompt 1> date
I'm running
In the parent.. wait
I'm running
In the child
Fri Sep 12 07:42:28 ICT 2014
5288 done
prompt 2> pwd
I'm running
In the parent.. wait
I'm running
In the child
/home/wiroon/os
5289 done