// CS 450; Threads can have local data; they share
//     global data
// version 2014-01-28 7:45 PM
//
#include <pthread.h>	// pthread_...
#include <stdio.h>
#include <stdlib.h>		// exit

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

int gv = 1;				// Global variable

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

	int my_x;  // Main's local variable

	// Create thread and have it run task
	//
	retcode = pthread_create(&thd, NULL, task, NULL);
	if (retcode != 0) {
		fprintf(stderr,
			"Thread creation failed with code %d!!\n",
			retcode );
		exit(1);
	}

	// Set & print value of local & global variables
	//
	my_x = 1234;
	gv = 5678;
	printf("Main:  &my_x = %-14p  my_x = %d\n",
		&my_x, my_x );
	printf("Main:  &gv   = %-14p  gv   = %d\n",
		&gv, gv );

	// Wait for child to finish, then reprint local & global
	// variables (only global variable will have changed).
	//
	pthread_join(thd, NULL);
	printf("Main has waited:\n");
	printf("Main:  &my_x = %-14p  my_x = %d\n", &my_x, my_x);
	printf("Main:  &gv   = %-14p  gv   = %d\n", &gv, gv);
}

// Task run by thread; this one changes its local
// variable and prints its value
//
void *task(void *arg) {
	int my_x;		// local variable
	my_x = 9012;
	gv = 3456;

	printf("Child: &my_x = %-14p  my_x = %d\n", &my_x, my_x);
	printf("Child: &gv   = %-14p  gv   = %d\n", &gv, gv);

	return NULL;
}

// Output:
// 
// Main:  &my_x = 0x7fff58187ac8  my_x = 1234
// Main:  &gv   = 0x107a79070     gv   = 5678
// Child: &my_x = 0x107b2cef4     my_x = 9012
// Child: &gv   = 0x107a79070     gv   = 3456
// Main has waited:
// Main:  &my_x = 0x7fff58187ac8  my_x = 1234
// Main:  &gv   = 0x107a79070     gv   = 3456