Operating systems Lab program: to develop C program to implement process management system calls

OPERATING SYSTEMS Lab [BCS303]
Department of CSE- Data Science

PRACTICAL COMPONENT OF IPCC(May cover all / major modules)
1. Develop a c program to implement the Process system calls (fork (), exec(),
wait(), create process, terminate process)
2. Simulate the following CPU scheduling algorithms to find turnaround time
and waiting time
a) FCFS b) SJF c) Round Robin d) Priority.
3. Develop a C program to simulate producer-consumer problem using
semaphores.
4. Develop a C program which demonstrates interprocess communication between
a reader process and a writer process. Use mkfifo, open, read, write and
close APIs in your program.

PRACTICAL COMPONENT OF IPCC contd…
5. Develop a C program to simulate Bankers Algorithm for DeadLock
Avoidance.
6. Develop a C program to simulate the following contiguous memory
allocation Techniques:
a) Worst fit b) Best fit c) First fit.
7. Develop a C program to simulate page replacement algorithms:
a) FIFO b) LRU
8. Simulate following File Organization Techniques
a) Single level directory b) Two level directory

PRACTICAL COMPONENT OF IPCC contd…
9. Develop a C program to simulate the Linked file allocation strategies.
10. Develop a C program to simulate SCAN disk scheduling algorithm.

Program 1: Develop a c program to implement the Process system calls (fork (),
exec(), wait(), create process, terminate process)
System Calls in Operating System
 A system call is a way for a user program to interface with the operating system.
 A system call is an interface between a program running in user space and
the operating system (OS).
 Application programs use system calls to request services and functionalities
from the OS's kernel.

 System calls are required in the following situations
- If a file system requires the creation or deletion of files. Reading and
writing from files also require a system call.
- Creation and management of new processes.
- Network connections also require system calls. This includes sending
and receiving packets.
- Access to a hardware devices such as a printer, scanner etc. requires a
system call

Fig: Execution of the system call

fork()
 Used to create new processes.
 The new process consists of a copy of the address space of the original
process.
 The value of process id for the child process is zero, whereas the value of
process id for the parent is an integer value greater than zero.

 Algorithm
1. Declare two variables pid and childid.
2. Get the childid value using system call fork().
3. If childid > zero then
print as “i am in the parent process”
retrieve process ID (PID) and its parent process ID (PPID) using getpid()
and getppid()
else
print “ i am in child process”
retrieve process ID (PID) and its parent process ID (PPID) using getpid()
and getppid()

getpid() Method
 The PID of the calling process is returned by the getpid() method, which is a
distinctive identification given to each active process in the system.
 Note: Every time you execute the program, the actual PID value (for example, 1234)
will change because it depends on the system and the status of the running
processes.
getppid() Method
 The PID of the calling process's parent process is returned by the getppid() method.
 The PID of the process that initiated the current process is thus retrieved.
 Note: The actual PPID value (for instance, 5678) will change depending on the
system and the active parent process, much like with the getpid() function.

Wait()
 The parent waits for the child process to complete using the wait system call.
The wait system call returns the process identifier of a terminated child, so that
the parent can tell which of its possibly many children has terminated.
 Syntax: wait (NULL);
exit ( )
 A process terminates when it finishes executing its final statement and asks the
operating system to delete it by using the exit system call.
 At that point, the process may return data (output) to its parent process (via the
wait system call).
 Syntax: exit (0);

#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
int main( )
{
int i, pid;
pid=fork( );
if(pid== -1)
{
printf("fork failed");
exit(0);
}
else if(pid==0)
{
printf("n Child process starts");
for(i=0; i<5; i++)
{
printf("n Child process %d is called", i);
}
printf("n Child process ends");
}
else
{
wait(0);
printf("n Parent process ends");
}
exit(0);
}

exec
 The exec family of functions replaces the current running process with a
new process.
 It can be used to run a C program by using another C program. It comes
under the header file unistd.h.
 There are many members in the exec family
i. execvp()
ii. execv()
iii. execlp()
iv. execl()

execv()
 replaces the currently executing program with a newly loaded program image.
 This occurs within one process; the process id is unchanged.
 The pathname of the program to run is passed as program.
#include<stdio.h>
#include<sys/types.h>
main(int argc,char *argv[])
{
printf("before execvn");
execv("/bin/ls",argv);
printf("after execvn");
}

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