I've made a few change to my workaround:
replaced the "sleep(1)" with:
PHP Code:
$sleep_random = (rand(0,5)) * 100000;
usleep(500000+$sleep_random);
and avoided to delete an unexistant key, replacing:
PHP Code:
if (isset($this->_redis, $this->_lock_key) && $this->_lock)
with:
PHP Code:
if (isset($this->_redis, $this->_lock_key) && $this->_lock && $this->_redis->exists($this->_lock_key))