Do Java sockets support full duplex?

Question

Is it possible to have one thread write to the OutputStream of a Java Socket, while another reads from the socket's InputStream, without the threads having to synchronize on the socket?

Answer 1

Sure. The exact situation you're describing shouldn't be a problem (reading and writing simultaneously).

Generally, the reading thread will block if there's nothing to read, and might timeout on the read operation if you've got a timeout specified.

Since the input stream and the output stream are separate objects within the Socket, the only thing you might concern yourself with is, what happens if you had 2 threads trying to read or write (two threads, same input/output stream) at the same time? The read/write methods of the InputStream/OutputStream classes are not synchronized. It is possible, however, that if you're using a sub-class of InputStream/OutputStream, that the reading/writing methods you're calling are synchronized. You can check the javadoc for whatever class/methods you're calling, and find that out pretty quick.

Answer 2

Yes, that's safe.

If you wanted more than one thread reading from the InputStream you would have to be more careful (assuming you are reading more than one byte at a time).