Question

Is there any possibility to set unique ID for a thread? In distributed system where threads are created on many different machines (e.g. by RMI)?

I need it to create log messages. From my research I know that it can be done using log4j mdc/ndc, but only in single thread. My problem is that ID has to be set when thread is created (to use the same ID for threads on different JVM but for the same request)

I am new to distributed systems.

Answer 1

If you want to have a globally unique request id, you can use the prcoessAndName (see below) with a counter and pass this with your message/request and use this to set the thread name.

public void processRequest(String uniqueRequestId, args) {
    Thread t = Thread.currrentThread();
    String tName = t.getName();
    try {
        t.setName("Processing " + uniqueRequestId);
        // preform process request
    } finally {
        t.setName(tName);
    }
}

This way the thread’s name will contain the request id regardless of which thread/machine it is run in. If you include the thread’s name in the logs, it will be included.

---

You can set the name of your thread using

String processAndHost = ManagementFactory.getRuntimeMXBean().getName()

You can append to this a descriptive name or counter.

This way all your thread names will be unique.

You can assume this name is globally unique provided, a) you have a unique hostname b) the process is not restarted so often there is a significant risk of two clients (at different times) with the same process id on the same host being a problem.

This can be combined with a locally unique id, to get a distributed unique id.

ExecutorService service = Executors.newCachedThreadPool(new ThreadFactory() {
    final String processName = ManagementFactory.getRuntimeMXBean().getName();
    final AtomicLong counter = new AtomicLong();
    @Override
    public Thread newThread(Runnable r) {
        String name = processName+"-"+counter.getAndIncrement();
        return new Thread(r, name);
    }
});
for(int i=0;i<10;i++)
    service.submit(new Runnable() {
        @Override
        public void run() {
            System.out.println("["+Thread.currentThread().getName()+"] - Hello World.");
            Thread.yield();
        }
    });
service.shutdown();

prints

[9480@myhost-0] - Hello World.
[9480@myhost-3] - Hello World.
[9480@myhost-2] - Hello World.
[9480@myhost-1] - Hello World.
[9480@myhost-5] - Hello World.
[9480@myhost-4] - Hello World.
[9480@myhost-6] - Hello World.
[9480@myhost-7] - Hello World.
[9480@myhost-0] - Hello World.
[9480@myhost-7] - Hello World.