The computer channel can't be used in ComputerListeners because it's closed before the call to listeners is done.
It causes a problem - you can't run any command in slave computer as part of "onOffline" method because the channel closed before the method called.

e.g (selenium-plugin)
VirtualChannel mainChannel = computer.getChannel();
if (mainChannel != null) {
try {
mainChannel.call(new StopSeleniumServer(name));
} catch (Exception e) {
e.printStackTrace();
try {
mainChannel.call(new RunningRemoteSetterCallable(name, "Error"));
} catch (Exception e1) {
e1.printStackTrace();
}
}
}