I'm making a port scanner for fun, not to be used in practice, since nmap is far, far better than anything I can make.

But I'm having an issue with multithreading. The scanner sends data, gets data back, but I'm looking for a way to close a thread once the data is received.

Currently, I use a timeout method, but that's not really the fastest or most efficient way, because a thread doesn't need to hang open for 1 second or even a half of a second, when the data was already received 0.8 seconds ago and the thread is no longer being used and is not needed.

I'd like to find a way to close those threads that are no longer needed because I'm hitting the thread limit and it'll make the whole loop run faster if I can trim the fat once I'm done with it.

It currently scans 25565 ports in 27 seconds on my machine, with a timeout specifically tuned for my system. But that doesn't mean it would work on other systems.

[Edit]

Stack overflow has multiple answers roughly amounting to, "it's not safe to close threads!"

But what I'm wondering is, is it safe to close the thread considering I can guarantee that it's completely stagnant, not being used, and it's task has been completed?

I could just have some kind of flag like "if data received does not equal null, close thread". Is that still considered unsafe?