rc_object.c

#define _POSIX_C_SOURCE 200809L
#include <stdio.h>
#include <stdlib.h>
#include <stdatomic.h>
#include <string.h>
#include <pthread.h>

typedef struct rc_object rc_object;

struct rc_object {
    atomic_int refcnt;
    void (*destroy)(rc_object *);
    char payload[64];
};

static rc_object *rc_new(const char *msg)
{
    rc_object *o = malloc(sizeof(rc_object));
    if (!o) return NULL;
    atomic_init(&o->refcnt, 1);
    o->destroy = NULL;
    strncpy(o->payload, msg, sizeof(o->payload) - 1);
    o->payload[sizeof(o->payload) - 1] = 0;
    return o;
}

static void rc_set_destroy(rc_object *o, void (*fn)(rc_object *))
{
    o->destroy = fn;
}

static rc_object *rc_acquire(rc_object *o)
{
    atomic_fetch_add_explicit(&o->refcnt, 1, memory_order_relaxed);
    return o;
}

static void rc_release(rc_object *o)
{
    int old = atomic_fetch_sub_explicit(&o->refcnt, 1, memory_order_acq_rel);
    if (old == 1) {
        if (o->destroy) o->destroy(o);
        free(o);
    }
}

static void rc_print(rc_object *o)
{
    printf("rc_object[%p]: %s\n", (void *)o, o->payload);
}

static void custom_destroy(rc_object *o)
{
    printf("destroying %p with payload=%s\n", (void *)o, o->payload);
}

typedef struct {
    rc_object *o;
} arg_t;

static void *worker(void *p)
{
    arg_t *a = p;
    rc_object *o = rc_acquire(a->o);
    rc_print(o);
    rc_release(o);
    return NULL;
}

int main(void)
{
    rc_object *o = rc_new("shared object");
    if (!o) return 1;
    rc_set_destroy(o, custom_destroy);
    pthread_t th[4];
    arg_t a;
    a.o = o;
    for (int i = 0; i < 4; i++) {
        pthread_create(&th[i], NULL, worker, &a);
    }
    for (int i = 0; i < 4; i++) {
        pthread_join(th[i], NULL);
    }
    rc_release(o);
    return 0;
}