Thread barrier shared between Go and C

coop.go

package main

// static void barrier_wait(int *barrier)
// {
//     int v = __atomic_add_fetch(barrier, 1, __ATOMIC_SEQ_CST);
//     if (v & 1) {
//         v &= 2;
//         while ((__atomic_load_n(barrier, __ATOMIC_SEQ_CST)&2) == v);
//     }
// }
//
// static void other(int *barrier, int *x, int n)
// {
//     for (int i = 0; i < n; i++) {
//         if (*x) *(volatile int *)0 = 0;
//         *x = 1;
//         barrier_wait(barrier);
//         barrier_wait(barrier);
//     }
// }
import "C"
import (
	"fmt"
	"sync/atomic"
)

func BarrierWait(barrier *int32) {
	v := atomic.AddInt32(barrier, 1)
	if v&1 == 1 {
		v &= 2
		for atomic.LoadInt32(barrier)&2 == v {
		}
	}
}

func main() {
	const n = 4_000_000
	var barrier, x int32
	go C.other((*C.int)(&barrier), (*C.int)(&x), n)
	for i := 0; i < n; i++ {
		BarrierWait(&barrier)
		if x != 1 {
			panic(x)
		}
		x = 0
		BarrierWait(&barrier)
	}
	fmt.Println("success")
}