basic-thread.c

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

// When building, you must link with the external pthread library: for example, 'gcc basic-thread.c -lpthread'

void* run(void* argument) {
    char* a = (char*) argument;
    printf("Provided argument: %s.\n", a);
    int* return_value = malloc(sizeof(int));
    *return_value = 99;
    pthread_exit(return_value);
}

int main(int argc, char** argv) {
    if (argc != 2) {
        printf("Invalid arguments.\n");
        return -1;
    }
    pthread_t t;
    void* vr;

    pthread_create(&t, NULL, run, argv[1]);
    pthread_join(t, &vr);
    int* r = (int*) vr;
    printf("The other thread returned the value: %d.\n", *r);
    free(vr);
    pthread_exit(0);
}

/*
    In this example, both threads are sharing the global variable "sum".
    We have some form of co-ordination here because the parent thread will
    join the newly-spawned thread (i.e wait until it is finished) before
    it tries to print out the value. If it did not join the spawned thread,
    the parent thread woudl print out the sum early.
*/