// CS 450; Thread example 3: Get result from thread
// version 2014-01-25 3:43 PM
//
#include <pthread.h>
#include <stdio.h>

void *task(void *arg);  // prototype

int main(void) {
	pthread_t thd;		// thread
	int retcode;		// 0 if thread creation succeeded
	int thd_arg = 17;

	// Create thread and have it run task; pass
	// (pointer to) thread argument
	//
	retcode = pthread_create(&thd, NULL, task, (void *) &thd_arg);
	printf("Thread creation returned code = %d\n", retcode);

	int *resultptr;
	pthread_join(thd, (void **) &resultptr);
	printf("result at %p\n", resultptr);
	if (resultptr != NULL) {
		printf("result = %d\n", *resultptr);
	}
}

int nonlocal; // task will return ptr to this variable
			  // task can't return ptr to local variable

// Task returns pointer to its result
//
void *task(void *arg) {
	int my_arg = *(int *) arg;
	printf("Thread called with argument %d\n", my_arg);

	nonlocal = my_arg * 2;
	printf("nonlocal at %p\n", &nonlocal);
	return &nonlocal;
}

/* Output

Thread creation returned code = 0
Thread called with argument 17
nonlocal at 0x100001078
result at 0x100001078

*/