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order_fence.c
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Thu, Feb 27, 02:08

order_fence.c
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#define _GNU_SOURCE
#include <pthread.h>
#include <omp.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
volatile int X, Y, r1, r2;
volatile bool t1block, t2block, t1fin, t2fin;
void *thread1Func(void *param){
for(;;){
while(t1block); // Wait for blocker to be removed
t1block = true; // Set up blocker
X = 1;
asm volatile("mfence" ::: "memory"); // Prevent any compiler reordering
r1 = Y;
t1fin = true; // Signal iteration end
}
return NULL; // Never returns
}
void *thread2Func(void *param){
for(;;){
while(t2block); // Wait for blocker to be removed
t2block = true; // Set up blocker
Y = 1;
asm volatile("mfence" ::: "memory"); // Prevent any compiler reordering
r2 = X;
t2fin = true; // Signal iteration end
}
return NULL; // Never returns
}
int main(){
//Init
t1block = t2block = true; // Act as blockers for threads
t1fin = t2fin = false; // Act as finish signals for threads
// Spawn the threads
pthread_t thread0, thread1, thread2;
thread0 = pthread_self();
pthread_create(&thread1, NULL, thread1Func, NULL);
pthread_create(&thread2, NULL, thread2Func, NULL);
/* Set the main thread affinity to CPU 0 */
cpu_set_t cpuset;
CPU_ZERO(&cpuset);
CPU_SET(0, &cpuset);
int s = pthread_setaffinity_np(thread0, sizeof(cpu_set_t), &cpuset);
if (s != 0){
printf("Failed to set main thread affinity\n");
return 0;
}
// Repeat the experiment
int detected = 0, i = 1;
for (i = 1; i < 1000000; i++){
// Reset all variables
X = 0;
Y = 0;
t1fin = t2fin = false;
t1block = t2block = false;
// Wait for threads to complete their iteration
while(!(t1fin && t2fin));
// Check if there was a memory reordering
if (r1 == 0 && r2 == 0){
detected++;
}
}
printf("%d memory re-orderings detected in %d iterations - %d percent\n", detected, i, 100*detected/i);
return 0; // Never returns
}

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