Operating System- CS604 Assignment # 1 Solution Fall 2010

Operating System- CS604

Assignment # 1

Solution

Fall 2010

                                                               Marks: 20

Due Date

Your assignment must be uploaded before or on 8^thNov 2010.

Objective

The objective of this assignment is to familiarize with the fork ( ), exit ( ) and wait ( ) system calls.

Instructions

Ø  Avoid Plagiarism. No marks will be given in case of cheating or copying from the internet or from other students.

Ø  Submit the assignment through your account on VULMS. No assignment will be accepted through email after the due date.  

Ø  If you have any problem related to assignment, feel free to discuss it by email at cs604@vu.edu.pk

Question # 1:

Understand the below program carefully and explain each line accordingly.

                               #include <stdio.h>

                               void main ( )

1………………… {

2……………………….int pid, status;

3……………………….pid = fork ( );

4……………………….if (pid = = -1)

5……………………… {

6……………………………printf(“fork failed\n”);

7……………………………exit(1) ;

8……………………….}

9………………………if (pid = = 0)

10……………………… {       

11………………………... printf( “Child here ! \n”);

12………………………... exit (0);

13……………………….}

14……………………….else

15……………………… {     

16………………………… wait (&status);

17………………………… printf(“well done kid !\n”);

18………………………… exit (0);

19……………………….}

20………………….}

1	{	Starting the main ( ) function.
2	int  pid, status;	Declaring two integer variables pid & status.
3	pid = fork ( );	The fork ( ) method will call and store the integer value in the pid variable. In case of Child “0” value returned while the parent will store the “process id” of the child. In case when fork fails it will be initialized by -1
4	if (pid = = -1)	This condition will be only true when fork failed.
5	{	Starting the if block (when fork failed)
6	printf(“fork failed\n”);	“fork failed “ message will be printed on screen.
7	exit(1) ;	The exit (1) system call will terminate the process and will return 1 to the parent process to indicate the abnormal termination.
8	}	if block ends.
9	if (pid = = 0)	This condition will be only true in case of Child Process because fork will return 0.
10	{	Starting the if block
11	printf( “Child here ! \n”);	“Child here!” message on screen
12	exit (0);	The exit (0) system call will terminate the process normally and will return 0 to parent process.
13	}	if block ends.
14	else	This block of code will be executed in the case of Parent Process only because fork returns ID of Child Process to parent process, which is not 0.
15	{	else block starts.
16	wait (&status);	Wait system call will suspend the parent process until the child process is terminated and returns 0 value through exit system call status and the parameter passed by child process 0 will be stored in status variable.
17	printf(“well done kid !\n”);	“well done kid!” message on screen
18	exit (0);	The exit (0) system call will terminate the parent process normally.
19	}	else block ends.
20	}	main ( ) function ends.