#include <pthread.h>

#include <stdio.h>

/**

* This function uses a thread that modifies a value on the stack

* of the main thread, hence will only work when all threads have access to the

* same shared memory.

*/

struct threadArgs

{

int idx;

int* ptr;

};

void* threadFunc(void* arg)

{

// Write to the struct passed in

auto args = (threadArgs*)arg;

*args->ptr = 200 + args->idx;

return nullptr;

}

int main()

{

// Spawn a couple of threads

int nThreads = 4;

int x[nThreads];

pthread_t threads[nThreads];

struct threadArgs args[nThreads];

for (int i = 0; i < nThreads; i++) {

args[i].idx = i;

args[i].ptr = &x[i];

int ret = pthread_create(&threads[i], NULL, threadFunc, &args[i]);

if (ret != 0) {

fprintf(stderr, "Error creating thread (%i)\n", ret);

return 1;

}

}

// Join the threads

for (int i = 0; i < nThreads; i++) {

if (pthread_join(threads[i], nullptr)) {

fprintf(stderr, "Error joining thread\n");

return 1;

}

// Check stack variable

int expected = 200 + i;

if (x[i] != expected) {

printf("Thread invocation failed (expected %i but got %i)\n",

expected,

x[i]);

return 1;

}

}

return 0;

}