example5_04.cpp

//顺序一直隐含着总体顺序
#include <atomic>
#include <thread>
#include <assert.h>

std::atomic<bool> x,y;
std::atomic<int> z;

void write_x()
{
	x.store(true,std::memory_order_seq_cst);
}

void write_y()
{
	y.store(true,std::memory_order_seq_cst);
}

void read_x_then_y()
{
	while(!x.load(std::memory_order_seq_cst));
	if(y.load(std::memory_order_seq_cst))
		++z;
}

void read_y_then_x()
{
	while(!y.load(std::memory_order_seq_cst));
	if(x.load(std::memory_order_seq_cst))
		++z;
}

int main()
{
	x=false;
	y=false;
	z=0;
	std::thread a(write_x);
	std::thread b(write_y);
	std::thread c(read_x_then_y);
	std::thread d(read_y_then_x);
	a.join();
	b.join();
	c.join();
	d.join();
	assert(z.load()!=0);
}