Memory Ordering

test_memory_ordering.cpp

//
//  main.cpp
//  test_volatile
//
//  Created by yiwei yang on 11/30/21.
//

#include <iostream>
#include <stdio.h>
#include <assert.h>
#include <atomic>

using namespace std;
atomic_uint y;
atomic_uint x;
volatile int r2;
volatile int r1 ;
bool assigned_42;


void *writer(void *unused) {
    r1 = x.load(memory_order_relaxed);
    
    y.store(r1, memory_order_relaxed);
    return NULL;
}

void *reader(void *unused) {
    bool assigned_42(false);
    r2 = y.load(memory_order_relaxed);
    if (r2 != 42) {
        assigned_42 = true;
        r2 = 42;
    }
    x.store(r2, memory_order_relaxed);
    assert(!assigned_42);
    return NULL;
}

int main(int argc, const char * argv[]) {
    // insert code here...
    for (int i=0;i<1000000;i++){
        y=0;
    pthread_t writer_thread;
    pthread_t reader_thread;
    pthread_create(&writer_thread, NULL, writer, NULL);
    pthread_create(&reader_thread, NULL, reader, NULL);
    pthread_join(reader_thread, NULL);
    pthread_join(writer_thread, NULL);}
    return 0;
}

line 3 will get into assertion.