Shutdown server abnormal

Question

I have a server accept multi connection from clients, When server down abnormal (power off, cable break ..), client need status of server
Can I setup timeout for client ?
How do I solve this task,?

Answer 1

When you lose your network connection your client will not be notified if the loss is due to a hard failure such as the cable being broken or the server having a power failure. You will need a keepalive mechanism. There is a built in keepalive in TCP that you can enable with setKeepAlive, unfortunately the default timeout is 2 hours. This value is also global on a system and not easy to adjust.
For this reason if you have control of the design of the protocol you should add a keepalive message. The message should be short, unique and should do nothing except be responded to by the server.
You will need a Timer, if you use the java.util.timer you should set it to run a task on a regular basis, such as every second. The timer task will run in a seperate thread, so you must be careful what you do with it. Be sure to cancel the timer when your done with it.
Every time you send or receive data, record the time. When the timer task runs check if the time since the last i/o is longer than your keepalive time, if so send the keepalive.
An attempt to send to a lost connection will get an exception. this will tell your client to shut down.
If you don't have control of the protocol and can't add a keepalive message, you can use the same timer approach, except attempt to make another connection when you time out. If you are using JDK 1.5 you can use the InetAddress.isReachable instead of connecting to your server port.