Write a C program using Pthreads on Linux that acts like a countdown timer alarm

Question

Write a C program using Pthreads on Linux that acts like a countdown timer alarm: The program implements a timer with two threads When the program starts, prompt the user for a number of seconds to set the timer (look into using scanf() to do this) Start two threads: 1. A thread that waits for a notification that the timer expired; when the timer expires, this thread should print a message that the timer has expired 2. A thread that will wait for the specified number of seconds (look into sleep() for this) and then sends a notification to the other thread that the timer has expired

Explanation / Answer

// Note: Please provide thumbs-up if you like the solution

// FileName: alarm_timer.c
// Follow below steps to run and see the output //
/*
$ gcc -o alarm_timer alarm_timer.c -lpthread
$ ./alarm_timer
Enter number of seconds to set timer:
2
go to sleep for 2 seconds ...
after go to sleep for seconds ...
Alarm bursted
$

*/
#include<stdio.h>
#include<pthread.h>
#include<semaphore.h>

sem_t mutex1;
sem_t mutex2;

void *read_alarm(void* arg)
{
   // call wait on mutex 1, this will allow thread to wait as initial value is 0, until post is called by start_alarm function
   sem_wait(&mutex1);
   printf("Alarm bursted ");
}

void *start_alarm(void* arg)
{
   // call wait on mutex 2, this will allow thread to enter the critical section as initial value is 1
   sem_wait(&mutex2);
   int *seconds=(int*) arg;
   printf("go to sleep for %d seconds ... ", *seconds);
   sleep(*seconds);
   printf("after go to sleep for seconds ... ");
   sem_post(&mutex1);
}

int main()
{  
   int timer;
  
   // initlizes semaphore with 0
   sem_init(&mutex1,0,0);
   // initlizes semaphore with 1
   sem_init(&mutex2,0,1);
  
   pthread_t tid[2];
   printf("Enter number of seconds to set timer: ");
   scanf("%d", &timer);
  
   // creates a thread and call start_alarm, pass timer input by user
   pthread_create(&tid[0], NULL, start_alarm, (void*)&timer);
   // creates a thread and call read_alarm
   pthread_create(&tid[1], NULL, read_alarm, (void*)&timer);
  
   // call join on created threads
   pthread_join(tid[0], NULL);
   pthread_join(tid[1], NULL);
  
   // call pthread_exit to wait till all threads have finished execution
   pthread_exit(0);
  
   // clean semaphores
   sem_destroy(&mutex1);
   sem_destroy(&mutex2);
   return 0;
}

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