APC: get a key’s expiration time

It’s always surprising to me, but APC is still the best kept secret.

APC offers a bunch of very useful features — foremost a realpath cache and an opcode cache. However, my favorite is neither: it’s being able to cache data in shared memory. How so? Simple: use apc_store() andapc_fetch() to persist data between requests.

The other day, I wanted use a key’s expiration date to send the appropriate headers (Expires and Last-Modified) to the client, but it didn’t seem like APC supports this out of the box yet.

Here is more or less a small hack until there’s a native call:

 * Return a key's expiration time.
 * @param string $key The name of the key.
 * @return mixed Returns false when no keys are cached or when the key
 *               does not exist. Returns int 0 when the key never expires
 *               (ttl = 0) or an integer (unix timestamp) otherwise.
function apc\_expire($key) {
    $cache = apc\_cache\_info('user');
    if (empty($cache['cache\_list'])) {
        return false;
    foreach ($cache['cache\_list'] as $entry) {
        if ($entry['info'] != $key) {
        if ($entry['ttl'] == 0) {
            return 0;
        $expire = $entry['creation_time']+$entry['ttl'];
        return $expire;
    return false;


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