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Sequential writing of volatile (C) and atomic (C++) and dead-store elimination
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
volatile char toggle = 1;
void *writer(void *unused) {
for (;;) {
toggle = 1;
toggle = 2;
}
return unused;
}
int main() {
pthread_t writer_thread;
pthread_create(&writer_thread, NULL, &writer, NULL);
long ones = 0, twos = 0;
for (int i = 0; i < 100000; i++) {
if (toggle == 1) {
ones++;
} else {
twos++;
}
}
printf("Ones: %ld; twos: %ld\n", ones, twos);
}
#include <iostream>
#include <thread>
#include <atomic>
#include "limits.h"
std::atomic<char> toggle;
void writer() {
for (;;) {
toggle.store(1);
toggle.store(2);
}
}
int main() {
std::thread writer_thread(writer);
toggle.store(1);
long ones = 0, twos = 0;
for (int i = 0; i < INT_MAX; i++) {
if (toggle.load() == 1) {
ones++;
} else {
twos++;
}
}
std::cout << "Ones: " << ones << "; twos: " << twos << "\n";
}
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