flush

public function flush(int $timeoutMs): int {}

Wait until all outstanding produce requests, et.al, are completed.
This should typically be done prior to destroying a producer instance to make sure
all queued and in-flight produce requests are completed before terminating.
This function will call poll() and thus trigger callbacks.

$conf = SimpleKafkaClient\Configuration();
$conf->set('metadata.broker.list', 'kafka:9092');
$producer = new SimpleKafkaClient\Producer($conf);
// produce some messsages
$producer->flush(10000);