Deadlocks$()$

$$ Deadlock in an operating system $($OS$)$ refers to a

situation where a set of processes are blocked

because each process is holding a resource and

waiting for another resource that is held by

another process. In this situation, none of the

processes can proceed, resulting in a standstill.

$$ Consider two processes, P$1$ and P$2,$ and two

resources, R$1$ and R$2$:

P$1$ holds R$1$ and is waiting for R$2.$

P$2$ holds R$2$ and is waiting for R$1.$

Both processes are blocked, waiting

indefinitely for each other to release the

resource they need, causing a deadlock.

$12$

Deadlocks$()$

$$ Deadlock Conditions:

For a deadlock to occur, all of the following conditions must be true simultaneously:

$1.$ Mutual Exclusion: A resource can be held by only one process at a time.

$2.$ Hold and Wait: Processes holding resources can request new ones.

$3.$ No Preemption: Resources cannot be preempted from processes holding them.

$4.$ Circular Wait: A circular chain of processes exists, where each process is waiting for a resource held by the

next process.

$13$

Program to create Deadlock Using C in Linux using Mutex Locks and threads

#include

#include

#include

void $*$function$1()$;

void $*$function$2()$;

pthread$\_$mutex$\_$t first$\_$mutex; $//$mutex lock

pthread$\_$mutex$\_$t second$\_$mutex;

int main$()\{$

pthread$\_$mutex$\_$init$($&first$\_$mutex,NULL$)$; $//$initialize

the lock

pthread$\_$mutex$\_$init$($&second$\_$mutex,NULL$)$;

pthread$\_$t one, two;

pthread$\_$create$($&one, NULL, function$1,$ NULL$)$; $//$

create thread

pthread$\_$create$($&two, NULL, function$2,$ NULL$)$;

pthread$\_$join$($one$,$ NULL$)$;

pthread$\_$join$($two$,$ NULL$)$;

printf$("$Thread joined

$")$;

$\}$

$14$

void $*$function$1()\{$

pthread$\_$mutex$\_$lock$($&first$\_$mutex$)$; $//$ to acquire the

resource$/$mutex lock

printf$("$Thread ONE acquired first$\_$mutex

$")$;

sleep$(1)$;

pthread$\_$mutex$\_$lock$($&second$\_$mutex$)$;

printf$("$Thread ONE acquired second$\_$mutex

$")$;

pthread$\_$mutex$\_$unlock$($&second$\_$mutex$)$; $//$ to release the

resource

printf$("$Thread ONE released second$\_$mutex

$")$;

pthread$\_$mutex$\_$unlock$($&first$\_$mutex$)$;

printf$("$Thread ONE released first$\_$mutex

$")$;

$\}$

void $*$function$2()\{$

pthread$\_$mutex$\_$lock$($&second$\_$mutex$)$;

printf$("$Thread TWO acquired second$\_$mutex

$")$;

sleep$(1)$;

pthread$\_$mutex$\_$lock$($&first$\_$mutex$)$;

printf$("$Thread TWO acquired first$\_$mutex

$")$;

pthread$\_$mutex$\_$unlock$($&first$\_$mutex$)$;

printf$("$Thread TWO released first$\_$mutex

$")$;

pthread$\_$mutex$\_$unlock$($&second$\_$mutex$)$;

printf$("$Thread TWO released second$\_$mutex

$")$;

$\}$

Lab Exercise

$$ Q$1.$ Write a program to simulate deadlock between three threads.

$$ Q$2.$ Write a program to create $4$ threads $($thread$1,$ thread$2,$ thread$3$ and

thread$4).$ Create a deadlock situation between thread$2$ and thread$4.$

Follow the concepts given and give me the codes for the above questions.

and also provide the output and explanation.