cas-thread.c

#include <stdint.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>

#define NCOUNT  (100000)
#define TCOUNT  (4)

volatile uint64_t u = 0;
volatile uint64_t *casvar = &u;

uint64_t
cas(volatile uint64_t *v, uint64_t old, uint64_t new)
{
        volatile uint64_t ret = 0;

        asm volatile (
            " add %0, zero, 1\n\t"
            " fence iorw, iorw\n\t"
            " lr.d.aq a0, (%1)\n\t"
            " bne %2, a0, done\n\t"
            " sc.d.rl %0, %3, (%1)\n\t"
            " fence iorw, iorw\n\t"
            "done:\n"
            : "+r" (ret)
            : "r" (v), "r" (old), "r" (new)
            : "a0"
        );

        return ret;
}

void *
thread(void *args) {
        volatile uint64_t val = 0;
        int i;

        for (i = 0; i < NCOUNT; i++) {
                for (;;) {
                        volatile uint64_t *vp = &val;
                        asm volatile (
                            " fence iorw, iorw\n\t"
                            " lr.d.aqrl a0, (%1)\n"
                            " fence iorw, iorw\n\t"
                            " sd a0, (%0)\n"
                            : "+r" (vp)
                            : "r" (casvar)
                            : "a0"
                        );
                        if (cas(casvar, val, val+1) == 0)
                                break;
                }
        }

        return (NULL);
}

int
main(int argc, char **argv)
{
        uint64_t        i;
        pthread_t       tid[TCOUNT];
        volatile uint64_t result;

        for (i = 0; i < TCOUNT; i++)
                pthread_create(&tid[i], NULL, thread, (void *)i+10);

        for (i = 0; i < TCOUNT; i++) {
                if (pthread_join(tid[i], NULL))
                        printf("pthread_join failed %d\n", i+10);
        }

        __atomic_load(casvar, &result, __ATOMIC_CONSUME);
        if (result != TCOUNT*NCOUNT) {
                printf("womp womp %d %d\n", result, TCOUNT*NCOUNT);
                return (1);
        }
        printf("ok %d %d\n", result, TCOUNT*NCOUNT);
        return (0);
}