Send Data from multiple threads to a single thread

Question

I'm coding a Java socket server that connects to Arduino which in turn send and receive data. As shown by the Java socket documentation I've set up the server to open a new thread for every connection.

My question is, how will I be able to send the data from the socket threads to my main thread? The socket will be constantly open, so the data has to be sent while the thread is running. Any suggestion?

Update: the goal of the server is to send commands to an Arduino (ie. Turn ligh on or off) and receive data from sensors, therefore I need a way to obtain that data from the sensors which are connected to individual threads and to send them into a single one.

Answer 1

Sharing data among threads is always tricky. There is no "correct" answer, it all depends on your use case. I suppose you are not searching for the highest performance, but for easiness of use, right?

For that case, I would recommend looking at synchronized collections, maps, lists or queues perhaps. One class, which seems like a good fit for you, is ConcurrentLinkedQueue.

You can also create synchronized proxies for all usual collections using the factory methods in Collections class:

    Collections.synchronizedList(new ArrayList<String>());

You do not have to synchronize access to them.

Another option, which might be an overkill, is using database. There are some in-memory databases, like H2.

In any case, I suggest you to lower the amount of shared information to the lowest possible level. For example, you can keep the "raw" data separate per thread (e.g. in ThreadLocal variables) and then just synchronize during aggregation.