Page History

...

For each member, another monitoring thread is checking the timestamp of its neighbor's HeartbeatMessage or any other messages received from its neighbor. Note that any message received from another member counts as a heartbeat. See GMSHealthMonitor.contactedBy(). If the member has not received the HeartbeatMessage from its neighbor for more than 5 seconds (the default for membership timeout / 2) which would usually be 2.5s. It will start sending HeartbeatRequestMessage to its neighbor to check whether its neighbor is still alive. If its neighbor is still alive, it will respond with HeartbeatMessage with requestID set to the same as HeartbeatRequestMessage. Upon receiving the response from its neighbor, the member will update its record of timestamp accordingly. If no response for HeartbeatRequestMessage is received from its neighbor, it will check its timestamp record again. It is possible that the neighbor has sent another HeartbeatMessage during the waiting period.

...