Java Programming

Hi!

I have to implement Singleton pattern, but I have the following restriction: The getInstance() method should not stop the entire application.

I wrote the following code, to achieve my objective:

public class ServiceProvider {
    private static Service service;
    private static final PrivateClass singletonProvider = new PrivateClass();
    
    private ServiceProvider() {}
    
    public static synchronized Service getInstance() throws MyException {
        if (service == null) {
            Thread thread = new Thread(singletonProvider);
            thread.start();
            
            try {
                // Ten seconds for the construction of the service field.
                Thread.sleep(10000);
            } catch (InterruptedException ex) {
                throw new MyException("InterruptedException!!!", ex);
            }
            
            // Is the verification based on Thread.isAlive() safe?
            // I am not sure. Please, tell me.
            if (!thread.isAlive()) {
                if (service == null) {
                    throw new MyException("Service is still not available");
                } else {
                    return service;
                }
            } else {
                throw new MyException("Service is still not available");
            }
            
        } else {
            return service;
        }
    }
    
    // Using a private class I do not need to expose the public run() method.
    private static class PrivateClass implements Runnable {
        private PrivateClass() {}
        
        private synchronized Service defineInstance() throws MyException {
            if (service == null) {
                service = new Service();
            }
            return service;
        }
        
        public synchronized void run() {
            try {
                singletonProvider.defineInstance();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

public class Service {
    public Service() throws MyException {
        try {
            // Simulating a problem: the constructor is taking 20 seconds to be finished.
            Thread.sleep(20000);
        } catch (InterruptedException ex) {
            throw new MyException("InterruptedException in the Service constructor", ex);
        }
    }

    public void method() {
        //...
    }
}

I am just not sure if the verification based on Thread.isAlive() is safe.


Thanks!!!