#include <assert.h>
#include <pthread.h>
#include <stdio.h>

#define N_THREADS 5


///  tls - a variable with storage automatically allocated locally for each
/// thread created (i.e. "thread-local storage")
static long __thread tls = 100; 


/**
 * A simple task to be run in multiple threads, which uses concurrently
 * accessed thread-local storage.
 */

void*
task(void* arg)
{
    long thread_id = (long)arg;
    tls = (thread_id % 2); // -> 0, 1, 0, 1, 0
    printf("  [task - thread %ld] tls = %ld.\n", thread_id, tls);
    pthread_exit(NULL);
}


// Forward decls
void launch_tasks(pthread_t* threads);
void end_tasks(pthread_t* threads);


int
main()
{
    pthread_t threads[N_THREADS];
    printf("[main] begin: tls = %ld\n", tls);
    launch_tasks(threads);
    end_tasks(threads);
    printf("[main] end: tls = %ld\n", tls);
    return 0;
}


/**
 * Run task in separate thread, using pthread_create. Exits if pthread_create
 * returns non-zero.
 */

void
launch_tasks(pthread_t* threads)
{
    for (size_t ctr=0; ctr<N_THREADS; ctr++) {
        int status = pthread_create(&threads[ctr], NULL, &task, (void*)ctr);
        assert((status==0 && "pthread_create returned non-zero status"));
    }
}


/**
 * Finalises task completion, by calling pthread_join on all threads. Exits if
 * pthread_join returns non-zero.
 */

void
end_tasks(pthread_t* threads)
{
    printf("[main] Joining threads\n");
    for (size_t ctr=0; ctr<N_THREADS; ctr++) {
        int status = pthread_join(threads[ctr], NULL);
        assert((status==0 && "pthread_join returned non-zero"));
    }
}