/* Copyright (C) 2024 Canonical Ltd

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License version 3 as
   published by the Free Software Foundation.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/* Build with gcc cfs.c -o cfs */

#define _GNU_SOURCE

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

#define FIRST_CORE 0

int calls_on_thread1 = 0;
int calls_on_thread2 = 0;

void *thread_start(void *arg)
{
        int thread_num = (intptr_t)arg;
        static bool make_thread1_nicer = false;

        static int calls_remaining = 100000;
        do {
                if (1 == thread_num) {
                        if (make_thread1_nicer) {
                                nice(19);
                                make_thread1_nicer = false;
                        }

                        calls_on_thread1++;
                } else
                        calls_on_thread2++;

                                                 /* Simulate doing some work */
                for (int i = 0; i < 20000; i++)
                        ;

        } while (--calls_remaining > 0);

        return (void *)NULL;
}

int main(void)
{
        pthread_t thread1, thread2;                            /* Thread IDs */
        pthread_attr_t attr1, attr2;

        /*-- Run on first core only --*/

        cpu_set_t cpu_set;
        CPU_ZERO(&cpu_set);
        CPU_SET(FIRST_CORE, &cpu_set);
        if (0 != sched_setaffinity(0, sizeof(cpu_set), &cpu_set)) {
                printf("Failed to set CPU affinity\n");
                exit(EXIT_FAILURE);
        }

        /*-- Prepare threads, assigning normal CFS-class scheduler --*/

        pthread_attr_init(&attr1);               /* Init thread's attributes */
        pthread_attr_setschedpolicy(&attr1, SCHED_OTHER);

        pthread_attr_init(&attr2);               /* Init thread's attributes */
        pthread_attr_setschedpolicy(&attr2, SCHED_OTHER);

        /*-- Call thread function on separate threads --*/

        if (0 != pthread_create(&thread1,
                                &attr1,
                                &thread_start,
                                (void *)(intptr_t)1)) {
                printf("Failed to create thread1\n");
                exit(EXIT_FAILURE);
        }

        if (0 != pthread_create(&thread2,
                                &attr2,
                                &thread_start,
                                (void *)(intptr_t)2)) {
                printf("Failed to create thread2\n");
                exit(EXIT_FAILURE);
        }

                              /* Ensure both threads are allowed to complete */
        pthread_join(thread1, NULL);
        pthread_join(thread2, NULL);

        printf("Calls made on thread1: %d\nCalls made on thread2: %d\n",
               calls_on_thread1,
               calls_on_thread2);

        exit(EXIT_SUCCESS);
}