Function cache_try_lock

modules/cache/cache_util.c:279–376

* Try obtain a cache wide lock on the given cache key. * * If we return APR_SUCCESS, we obtained the lock, and we are clear to * proceed to the backend. If we return APR_EEXIST, then the lock is * already locked, someone else has gone to refresh the backend data * already, so we must return stale data with a warning in the mean * time. If we return anything else, then something has gone pear

 * the backend.
 */
apr_status_t cache_try_lock(cache_server_conf *conf, cache_request_rec *cache,
        request_rec *r)
{
    apr_status_t status;
    const char *lockname;
    const char *path;
    char dir[5];
    apr_time_t now = apr_time_now();
    apr_finfo_t finfo;
    apr_file_t *lockfile;
    void *dummy;

    finfo.mtime = 0;

    if (!conf || !conf->lock || !conf->lockpath) {
        /* no locks configured, leave */
        return APR_SUCCESS;
    }

    /* lock already obtained earlier? if so, success */
    apr_pool_userdata_get(&dummy, CACHE_LOCKFILE_KEY, r->pool);
    if (dummy) {
        return APR_SUCCESS;
    }

    /* create the key if it doesn't exist */
    if (!cache->key) {
        cache_handle_t *h;
        /*
         * Try to use the key of a possible open but stale cache
         * entry if we have one.
         */
        if (cache->handle != NULL) {
            h = cache->handle;
        }
        else {
            h = cache->stale_handle;
        }
        if ((h != NULL) &&
            (h->cache_obj != NULL) &&
            (h->cache_obj->key != NULL)) {
            cache->key = apr_pstrdup(r->pool, h->cache_obj->key);
        }
        else {
            cache_generate_key(r, r->pool, &cache->key);
        }
    }

    /* create a hashed filename from the key, and save it for later */
    lockname = ap_cache_generate_name(r->pool, 0, 0, cache->key);

    /* lock files represent discrete just-went-stale URLs "in flight", so
     * we support a simple two level directory structure, more is overkill.
     */
    dir[0] = '/';
    dir[1] = lockname[0];
    dir[2] = '/';
    dir[3] = lockname[1];