Can Java ServerSocket and Sockets using ObjectIOStreams lose packets?

Question

I'm using a ServerSocket on my server and Sockets that use ObjectIOStreams to send serializable objects over the network connection. I'm developing an essentially more financial version of monopoly and thus packets being sent and confirmed as sent/received is required. Do I need to implement my own packet loss watcher or is that already taken care of with (Server)Sockets?

I'm primarily asking about losing packets during network blips or whatnot, not full connection error. E.g. siblings move a lead plate between my router and computer's wi-fi adapter.

http://code.google.com/p/inequity/source/browse/#svn/trunk/src/network Code can be found under network->ClientController and network->Server

Answer 1

Theoretically; yes. There is no way of giving 100 % theoretical guarantee that what is sent on the hardware layer, is received the same way on the receiving end.

Practically however, if you use TCP (Transmission Control Protocol) this stuff has already been taken care of; you won't loose any packets. (If you're using UDP on the other hand (User Datagram Protocol) it's another story, and it may very well be the case that you're loosing packets, or receiving them out of order).

Just looked briefly at your code, and it seems you're using multiple threads. If so you must be utterly careful with synchronization. It could very well be the case that it looks like a packet has been dropped, although, it is simply not handled due to a race condition in the program. (Keep in mind that the gui for instance, runs in its own thread.)

The best way to solve the synchronization, I think, is to put the network loop in a very small read/put-on-synchronized-queue loop, and pick up the received packets from the queue whenever you're sure no other thread will intervene.