williamboxhall / tcp-sockets Goto Github PK

Hi. First of all congrats on getting the job :)

There's one problem with your solution though - you're handling all user clients through blocking sockets in a single thread. That works well for provided test script, but won't work well if one of the clients decides to send his id with some delay (or won't send it at all).

Consider the following use case:

1. run your server
2. run telnet localhost 9099 (that connects a user client without sending his id)
3. run the provided test script (followermaze.sh)

You'll see that the first client (telnet) is preventing the others from connecting, and you'll see an error messages from test script after 20s deadline.

The bottom line is: one should not use blocking sockets with blocking operations in a single thread in a loop. Please look at these slides to see how it could be done. Slide 5 ("Classic ServerSocket Loop") shows how to handle your case (blocking sockets). The simplest fix would be to replace this line with something like this (Java 8):

new Thread(() -> router.connect(integerFrom(client), client)).start();

Although it might be a better idea to use ThreadPoolExecutor instead. It's also probably a good idea to set SO_TIMEOUT so that the client has some limited time for sending his id. Finally any exception in "client handler" should close the client connection and remove it from router's registry.

Best regards and see you soon :)
Tomasz

You did the impossible, you made Java code beautiful :)