public class Test {

    private static volatile long a = -1, b = -2;

    public static void main(String[] args) {
        long max = 1_000_000;
        new Thread(() -> {
            for (int i = 0; i < max; i++) {
                a = System.nanoTime();
            }
        }).start();
        new Thread(() -> {
            for (int i = 0; i < max; i++) {
                b = System.nanoTime();
            }
        }).start();
        for (int i = 0; i < max; i++) {
            if (a == b) {
                System.out.println("nanoTime not unique");
            }
        }
    }

}

public class BitShiftTest {

    private static String toBinaryString(int i) {
        return String.format("%32s", Integer.toBinaryString(i)).replace(' ', '0');
    }

    public static void main(String[] args) {
        int i = 0b00000000_00000000_00000000_00000001;
        int j = i << 35;
        System.out.println(j);
        System.out.println(toBinaryString(j));
    }

}

/**
 * This class holds a set of filenames to be deleted on VM exit through a shutdown hook.
 * A set is used both to prevent double-insertion of the same file as well as offer
 * quick removal.
 */
class DeleteOnExitHook {
    private static LinkedHashSet<String> files = new LinkedHashSet<>();
    static {
        // DeleteOnExitHook must be the last shutdown hook to be invoked.
        // Application shutdown hooks may add the first file to the
        // delete on exit list and cause the DeleteOnExitHook to be
        // registered during shutdown in progress. So set the
        // registerShutdownInProgress parameter to true.
        sun.misc.SharedSecrets.getJavaLangAccess()
            .registerShutdownHook(2 /* Shutdown hook invocation order */,
                true /* register even if shutdown in progress */,
                new Runnable() {
                    public void run() {
                       runHooks();
                    }
                }
        );
    }

    private DeleteOnExitHook() {}

    static synchronized void add(String file) {
        if(files == null) {
            // DeleteOnExitHook is running. Too late to add a file
            throw new IllegalStateException("Shutdown in progress");
        }

        files.add(file);
    }

    static void runHooks() {
        LinkedHashSet<String> theFiles;

        synchronized (DeleteOnExitHook.class) {
            theFiles = files;
            files = null;
        }

        ArrayList<String> toBeDeleted = new ArrayList<>(theFiles);

        // reverse the list to maintain previous jdk deletion order.
        // Last in first deleted.
        Collections.reverse(toBeDeleted);
        for (String filename : toBeDeleted) {
            (new File(filename)).delete();
        }
    }
}

@GuardedBy("isolatedEndpointsSetLock")
private final Set<Endpoints> isolatedEndpointsSet;
private final ReadWriteLock isolatedEndpointsSetLock;

public ProducerImpl(String group) throws ClientException {
    super(group);
    this.defaultSendCallbackExecutor = new ThreadPoolExecutor(
            Runtime.getRuntime().availableProcessors(),
            Runtime.getRuntime().availableProcessors(),
            60,
            TimeUnit.SECONDS,
            new LinkedBlockingQueue<Runnable>(),
            new ThreadFactoryImpl("SendCallbackWorker"));

    this.sendingRouteDataCache = new ConcurrentHashMap<String, SendingTopicRouteData>();

    this.isolatedEndpointsSet = new HashSet<Endpoints>();
    this.isolatedEndpointsSetLock = new ReentrantReadWriteLock();
}

/**
 * Check the status of isolated {@link Endpoints}, rejoin it if it is healthy.
 */
@Override
public void doHealthCheck() {
    final Set<Endpoints> routeEndpointsSet = getRouteEndpointsSet();
    final Set<Endpoints> expired = new HashSet<Endpoints>(Sets.difference(routeEndpointsSet, isolatedEndpointsSet));
    // remove all isolated endpoints which is expired.
    isolatedEndpointsSetLock.writeLock().lock();
    try {
        isolatedEndpointsSet.removeAll(expired);
    } finally {
        isolatedEndpointsSetLock.writeLock().unlock();
    }

    HealthCheckRequest request = HealthCheckRequest.newBuilder().build();
    isolatedEndpointsSetLock.readLock().lock();
    try {
        for (final Endpoints endpoints : isolatedEndpointsSet) {
            Metadata metadata;
            try {
                metadata = sign();
            } catch (Throwable t) {
                continue;
            }
            final ListenableFuture<HealthCheckResponse> future =
                    clientManager.healthCheck(endpoints, metadata, request, ioTimeoutMillis, TimeUnit.MILLISECONDS);
            Futures.addCallback(future, new FutureCallback<HealthCheckResponse>() {
                @Override
                public void onSuccess(HealthCheckResponse response) {
                    final Status status = response.getCommon().getStatus();
                    final Code code = Code.forNumber(status.getCode());
                    // target endpoints is healthy, rejoin it.
                    if (Code.OK.equals(code)) {
                        isolatedEndpointsSetLock.writeLock().lock();
                        try {
                            isolatedEndpointsSet.remove(endpoints);
                        } finally {
                            isolatedEndpointsSetLock.writeLock().unlock();
                        }
                        log.info("Rejoin endpoints which is isolated before, clientId={}, endpoints={}", id,
                                endpoints);
                        return;
                    }
                    log.warn("Failed to rejoin the endpoints which is isolated before, clientId={}, code={}, "
                            + "status message=[{}], endpoints={}", id, code, status.getMessage(), endpoints);
                }

                @Override
                public void onFailure(Throwable t) {
                    log.error("Failed to do health check, clientId={}, endpoints={}", id, endpoints, t);
                }
            });
        }
    } finally {
        isolatedEndpointsSetLock.readLock().unlock();
    }
}