What you have are two threads. One is the main thread (A); it creates a new thread (B). Both threads share a hashtable. The problem is how does thread (A) know what thread (B) is
doing?

The answer is as old as the first computer with multi-threading/tasking. It is threads talking to each other.

Set up a data structure next to the hashtable that is accessible to both threads. You say thread (B) wakes up periodically, a sleep time I assume.

long sleep_time = 10000L  // ten minutes in milliseconds

long last_awake = 0; // last time awake

Now when thread (B) awakens, it updates last_awake with the System.currentTimeMillis().

When thread (A) is curious about the health of thread (B), it can check that the last_awake (plus the sleep_time or something) is reasonable.

This is only one of MANY ways threads can talk to each other.

Sorry if this question has an obvious
answer.