Gamelift DescribePlayerSessions and synchronization

Hi,

In order to notify gamelift that players are accepted by my server, I have to call AcceptPlayerSession with a player session id. To obtain this player session id, I am using DescribePlayerSessions with the connecting player id as parameter.

1)I am wondering whether DescribePlayerSessions is the prefered method to obtain player session ids. If not do I have other ways?

2. Am I guaranted that by the time a player connects (which means that flexmatch successfully placed the player), DescribePlayerSessions will actually return the player session id or do I have to periodically poll?

To add some context, I'm using both Gamelift and Flexmatch.

Thanks, Nicolas.