An attempt at a periodic callback in nginx

cleanup_timer.c

#define NGX_HTTP_AUTH_DIGEST_CLEANUP_INTERVAL 3000
ngx_event_t *ngx_http_auth_digest_cleanup_timer;
static ngx_atomic_t *ngx_http_auth_digest_cleanup_lock;

// set as the "init process" callback in the ngx_module_t struct
static ngx_int_t ngx_http_auth_digest_worker_init(ngx_cycle_t *cycle){      
  if (ngx_process != NGX_PROCESS_WORKER){
     return NGX_OK;
  }

  ngx_connection_t  *dummy;
  dummy = ngx_pcalloc(cycle->pool, sizeof(ngx_connection_t));
  if (dummy == NULL) return NGX_ERROR;
  dummy->fd = (ngx_socket_t) -1;
  dummy->data = cycle;
  
  ngx_http_auth_digest_cleanup_timer->log = ngx_cycle->log;
  ngx_http_auth_digest_cleanup_timer->data = dummy;
  ngx_http_auth_digest_cleanup_timer->handler = ngx_http_auth_digest_cleanup;
  ngx_add_timer(ngx_http_auth_digest_cleanup_timer, NGX_HTTP_AUTH_DIGEST_CLEANUP_INTERVAL);

  return NGX_OK;
}

void ngx_http_auth_digest_cleanup(ngx_event_t *ev){
  // set up the next tick in n seconds
  ngx_add_timer(ev, NGX_HTTP_AUTH_DIGEST_CLEANUP_INTERVAL);

  // expire stale items from the rbtree
  if (ngx_trylock(ngx_http_auth_digest_cleanup_lock)){
    ngx_log_error(NGX_LOG_ERR, ev->log, 0, "cleanup");
    ngx_http_auth_digest_rbtree_prune(ev->log);
    ngx_unlock(ngx_http_auth_digest_cleanup_lock);    
  }else{
    ngx_log_error(NGX_LOG_ERR, ev->log, 0, "locked");
  }  
}