Question

Write a program hellomany.c that will create a number N of threads specified in the command line, each of which prints out a hello message and its own thread ID. To see how the execution of the threads interleaves, make the main thread sleep for 1 second for every 4 or 5 threads it creates. The output of your code should be similar to:

       I am thread 1. Created new thread (4) in iteration 0...
       Hello from thread 4 - I was created in iteration 0
       I am thread 1. Created new thread (6) in iteration 1...
       I am thread 1. Created new thread (7) in iteration 2...
       I am thread 1. Created new thread (8) in iteration 3...
       I am thread 1. Created new thread (9) in iteration 4...
       I am thread 1. Created new thread (10) in iteration 5...
       Hello from thread 6 - I was created in iteration 1
       Hello from thread 7 - I was created in iteration 2
       Hello from thread 8 - I was created in iteration 3
       Hello from thread 9 - I was created in iteration 4
       Hello from thread 10 - I was created in iteration 5
       I am thread 1. Created new thread (11) in iteration 6...
       I am thread 1. Created new thread (12) in iteration 7...
       Hello from thread 11 - I was created in iteration 6
       Hello from thread 12 - I was created in iteration 7

Answer 1

The program for the given problem is given below -

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>

//Let us Define maximum number of threads so that it doesn't run endlessly
#define NUMBER 50

pthread_t thread_id[NUMBER];

//Function to create thread.
void * createThread(void * threadNum){
printf("Hello from thread %u - I was created in iteration %d \n",(int)pthread_self(),(int)threadNum);
pthread_exit(NULL);
}

int main(){
int a, n;
printf(" Enter number of threads you want to make.");
scanf("%d",&n);
  
// If n is greater than our max threads then we put n = max number of threads.
if(n > NUMBER)
{
n = NUMBER;
}
for(int i = 0; i < n; i++)
{
// Creating thread
a = pthread_create(&thread_id[i], NULL, createThread, (void*)i);
  
//Error handling
if(a)
{
printf("\n ERROR: return code from pthread_create is %d \n", a);
exit(1);
}
  
  
printf("\n I am thread %u. Created new thread (%u) in iteration %d ...\n",
(int)pthread_self(), (int)thread_id[i], i);
  
// Making main thread sleep after every 5 seconds.
if(i % 5 == 0)
sleep(1);

}

  pthread_exit(NULL);

}

Code screenshot -

Code Output -

Note - In my output, thread id doesn't start from 1 because I was running my program in an online compiler. If you run this program in your system, it will start from 1.

Solution ends.

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Thank you.

Have a good day.