LABORATORY-6

Avoiding Race Condition using System Call in Linux

A signal is just like an interrupt when it is generated at the user level a call is made to the kernel of the OS, which then acts accordingly

a.) Maskable
b.) Non-Maskable

System Call: A system call is a procedure that provide the interface between a process and the OS. it is the way by which a computer program requests a service from the kernel of the OS.

Types of System Calls:-

            System  Calls:- 
	            a.) Process Control :-  fork(), exit(), exec()
	            b.) Device Management:- loctl();
	            c.) File Management:- open(), read(), write(), close()
	            d.) Information Maintenance:- getpid(), alarm(), sleep()
	            e.) Communication:- pipe(), shmget(), mmap()

SOME IMPORTANT SIGNALS:-

        1.) SIGPWR:- POWER FAILURE
        2.) SIGINT:- INTERRUPT FROM KEYBOARD
        3.) SIGILL:- ILLEGAL INSTRUCTION
        4.) SIGFPE:- FLOATING POINT EXECUTION
        5.) SIGSEGV:- INVALID MEMORY REFERENCE
        6.) SIGBUS:- BUS ERROR[BAD MEMORY ACCESS]
        7.) SIGIO:- I/O NOW POSSIBLE
        8.) SIGPIPE:- BROKEN PIPE: WITE THE PIPE WITH NO READERS.
        9.) SIGKILL:- KILL SIGNAL *
        10.) SIGSTOP:- STOP PROCESS
        11.) SIGTSTP:- STOPED TYPES AT TERMINAL
        12.) SIGUSR1:- USER DEFINED SIGNAL-1
        13.) SIGHUP:- HANGUP DETECTED ON CONTROLLING TERMINAL ON DEATH OF CONTROLLING PROCESS.
        14.) SIGALRM:- TIMER SIGNAL

Code for SIGINT

            #include "stdio.h"
            #include "unistd.h"
            #include "signal.h"
            void oh(int sig){
                printf("I got signal %d\n", sig);
                signal(SIGINT,oh);
            }
            int main(){
                signal(SIGINT,oh);
                while(1){
                    printf("Hello World!");
                    sleep(1);
                }
            }

Code for SIGKILL

            #include "stdio.h"
            #include "unistd.h"
            #include "signal.h"

            int main(){
                pid_t pid, ppid, cpid;
                ppid = getpid();
                pid = fork();
                if(ppid == getpid()){
                    printf("PARENT");
                }
                else if(cpid == getpid()){
                    printf("CHILD");
                }
                if(pid > 0){
                    int i = 0;
                    while(i++ < 10){
                        printf("In the parent process");
                        sleep(1);
                    }
                }
                else if(pid == 0){
                    int i=0;
                    while(i++ < 10){
                        printf("In the child process");
                        sleep(1);
                        if(i == 3){
                            kill(ppid,SIGKILL);
                            printf("Parent Killed, I'm Orphan!!!!!!!!!!);
                        }
                    }
                }
                else{
                    printf("Something bad happened");
                    exit(EXIT_FAILURE);
                }
                return 0;
            }

Code for SIGDFL

        #include "stdio.h"
        #include "unistd.h"
        #include "signal.h"

        void oh(int sig){
            printf("I got signal",sig);
            signal(SIGINT, SIG_DFL);
        }
        
        int main(){
            signal(SIGINT,oh);
            while(1){
                printf("Hello World\n);
                sleep(1);
            }
        }

Code for SIGQUIT

        #include "stdio.h"
        #include "unistd.h"
        #include "signal.h"

        void oh(int sig){
            printf("I got signal",sig);
            signal(SIGQUIT, oh);
        }
        
        int main(){
            signal(SIGQUIT,oh);
            while(1){
                printf("Hello World\n);
                sleep(1);
            }
        }

Code for SIGALRM

        #include "stdio.h"
        #include "unistd.h"
        #include "signal.h"

        void sig_oh(int sig){
            printf("ALARM TING TING........");
            signal(SIGALRM,sig_oh);
        }
        
        int main(){
            signal(SIGALRM,sig_oh);
            alarm(2);
            while(1){
                printf("Hello World\n");
                sleep(1);
            }
        }