Back-port fix for OPENDJ-1112: LoadBalancing connection factories need bett...

Matthew Swift

30.25.2013 ad636a8035cc19f5a412b6b97b3f95ba37d0fe9a

Back-port fix for OPENDJ-1112: LoadBalancing connection factories need better diagnostic messages

 opendj-ldap-sdk/src/main/java/org/forgerock/opendj/ldap/AbstractLoadBalancingAlgorithm.java

@@ -162,12 +162,17 @@
        }

        private void notifyOffline(final ErrorResultException error) {
            // Save the error in case the load-balancer is exhausted.
            lastFailure = error;

            if (isOperational.getAndSet(false)) {
                // Transition from online to offline.
                if (DEBUG_LOG.isLoggable(Level.WARNING)) {
                    DEBUG_LOG.warning(String.format(
                            "Connection factory '%s' is no longer operational: %s", factory, error
                                    .getMessage()));
                synchronized (listenerLock) {
                    try {
                        listener.handleConnectionFactoryOffline(factory, error);
                    } catch (RuntimeException e) {
                        handleListenerException(e);
                    }
                }

                synchronized (stateLock) {
@@ -189,9 +194,12 @@
        private void notifyOnline() {
            if (!isOperational.getAndSet(true)) {
                // Transition from offline to online.
                if (DEBUG_LOG.isLoggable(Level.INFO)) {
                    DEBUG_LOG.info(String.format("Connection factory'%s' is now operational",
                            factory));
                synchronized (listenerLock) {
                    try {
                        listener.handleConnectionFactoryOnline(factory);
                    } catch (RuntimeException e) {
                        handleListenerException(e);
                    }
                }

                synchronized (stateLock) {
@@ -207,6 +215,13 @@
                }
            }
        }

        private void handleListenerException(RuntimeException e) {
            if (DEBUG_LOG.isLoggable(Level.SEVERE)) {
                DEBUG_LOG.log(Level.SEVERE,
                        "A run-time error occurred while processing a load-balancer event", e);
            }
        }
    }

    private final class MonitorRunnable implements Runnable {
@@ -222,9 +237,54 @@
        }
    }

    /**
     * A default event listener which just logs the event.
     */
    private static final LoadBalancerEventListener DEFAULT_LISTENER =
            new LoadBalancerEventListener() {

                @Override
                public void handleConnectionFactoryOnline(ConnectionFactory factory) {
                    // Transition from offline to online.
                    if (DEBUG_LOG.isLoggable(Level.INFO)) {
                        DEBUG_LOG.info(String.format("Connection factory'%s' is now operational",
                                factory));
                    }
                }

                @Override
                public void handleConnectionFactoryOffline(ConnectionFactory factory,
                        ErrorResultException error) {
                    if (DEBUG_LOG.isLoggable(Level.WARNING)) {
                        DEBUG_LOG.warning(String.format(
                                "Connection factory '%s' is no longer operational: %s", factory,
                                error.getMessage()));
                    }
                }
            };

    private final List<MonitoredConnectionFactory> monitoredFactories;
    private final ReferenceCountedObject<ScheduledExecutorService>.Reference scheduler;
    private final Object stateLock = new Object();

    /**
     * The last connection failure which caused a connection factory to be
     * marked offline. This is used in order to help diagnose problems when the
     * load-balancer has exhausted all of its factories.
     */
    private volatile ErrorResultException lastFailure = null;

    /**
     * The event listener which should be notified when connection factories go
     * on or off-line.
     */
    private final LoadBalancerEventListener listener;

    /**
     * Ensures that events are notified one at a time.
     */
    private final Object listenerLock = new Object();

    /**
     * Guarded by stateLock.
     */
@@ -237,17 +297,9 @@
    private ScheduledFuture<?> monitoringFuture;
    private AtomicBoolean isClosed = new AtomicBoolean();

    AbstractLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories) {
        this(factories, 1, TimeUnit.SECONDS, null);
    }

    AbstractLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final long interval, final TimeUnit unit) {
        this(factories, interval, unit, null);
    }

    AbstractLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final long interval, final TimeUnit unit, final ScheduledExecutorService scheduler) {
            final LoadBalancerEventListener listener, final long interval, final TimeUnit unit,
            final ScheduledExecutorService scheduler) {
        Validator.ensureNotNull(factories, unit);

        this.monitoredFactories = new ArrayList<MonitoredConnectionFactory>(factories.size());
@@ -258,6 +310,7 @@
        this.scheduler = DEFAULT_SCHEDULER.acquireIfNull(scheduler);
        this.monitoringInterval = interval;
        this.monitoringIntervalTimeUnit = unit;
        this.listener = listener != null ? listener : DEFAULT_LISTENER;
    }

    @Override
@@ -335,6 +388,6 @@
         * timeout period.
         */
        throw newErrorResult(ResultCode.CLIENT_SIDE_CONNECT_ERROR,
                "No operational connection factories available");
                "No operational connection factories available", lastFailure);
    }
}

 opendj-ldap-sdk/src/main/java/org/forgerock/opendj/ldap/FailoverLoadBalancingAlgorithm.java

@@ -22,6 +22,7 @@
 *
 *
 *      Copyright 2010 Sun Microsystems, Inc.
 *      Portions copyright 2013 ForgeRock AS.
 */

package org.forgerock.opendj.ldap;
@@ -35,10 +36,10 @@
 * underlying connection factories.
 * <p>
 * This algorithm is typically used for load-balancing <i>between</i> data
 * centers, where there is preference to always forward connection
 * requests to the <i>closest available</i> data center. This algorithm
 * contrasts with the {@link RoundRobinLoadBalancingAlgorithm} which is used for
 * load-balancing <i>within</i> a data center.
 * centers, where there is preference to always forward connection requests to
 * the <i>closest available</i> data center. This algorithm contrasts with the
 * {@link RoundRobinLoadBalancingAlgorithm} which is used for load-balancing
 * <i>within</i> a data center.
 * <p>
 * This algorithm selects connection factories based on the order in which they
 * were provided during construction. More specifically, an attempt to obtain a
@@ -69,7 +70,70 @@
     *            The ordered collection of connection factories.
     */
    public FailoverLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories) {
        super(factories);
        this(factories, null, 1, TimeUnit.SECONDS, null);
    }

    /**
     * Creates a new fail-over load balancing algorithm which will monitor
     * offline connection factories every 1 second using the default scheduler.
     *
     * @param factories
     *            The ordered collection of connection factories.
     * @param listener
     *            The event listener which should be notified whenever a
     *            connection factory changes state from online to offline or
     *            vice-versa.
     */
    public FailoverLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final LoadBalancerEventListener listener) {
        this(factories, listener, 1, TimeUnit.SECONDS, null);
    }

    /**
     * Creates a new fail-over load balancing algorithm which will monitor
     * offline connection factories using the specified frequency using the
     * default scheduler.
     *
     * @param factories
     *            The connection factories.
     * @param listener
     *            The event listener which should be notified whenever a
     *            connection factory changes state from online to offline or
     *            vice-versa.
     * @param interval
     *            The interval between attempts to poll offline factories.
     * @param unit
     *            The time unit for the interval between attempts to poll
     *            offline factories.
     */
    public FailoverLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final LoadBalancerEventListener listener, final long interval, final TimeUnit unit) {
        this(factories, listener, interval, unit, null);
    }

    /**
     * Creates a new fail-over load balancing algorithm which will monitor
     * offline connection factories using the specified frequency and scheduler.
     *
     * @param factories
     *            The connection factories.
     * @param listener
     *            The event listener which should be notified whenever a
     *            connection factory changes state from online to offline or
     *            vice-versa.
     * @param interval
     *            The interval between attempts to poll offline factories.
     * @param unit
     *            The time unit for the interval between attempts to poll
     *            offline factories.
     * @param scheduler
     *            The scheduler which should for periodically monitoring dead
     *            connection factories to see if they are usable again.
     */
    public FailoverLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final LoadBalancerEventListener listener, final long interval, final TimeUnit unit,
            final ScheduledExecutorService scheduler) {
        super(factories, listener, interval, unit, scheduler);
    }

    /**
@@ -87,7 +151,7 @@
     */
    public FailoverLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final long interval, final TimeUnit unit) {
        super(factories, interval, unit);
        this(factories, null, interval, unit, null);
    }

    /**
@@ -107,7 +171,7 @@
     */
    public FailoverLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final long interval, final TimeUnit unit, final ScheduledExecutorService scheduler) {
        super(factories, interval, unit, scheduler);
        this(factories, null, interval, unit, scheduler);
    }

    /**

 opendj-ldap-sdk/src/main/java/org/forgerock/opendj/ldap/LoadBalancerEventListener.java

New file
@@ -0,0 +1,62 @@
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at legal-notices/CDDLv1_0.txt
 * or http://forgerock.org/license/CDDLv1.0.html.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at legal-notices/CDDLv1_0.txt.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information:
 *      Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 *
 *      Copyright 2013 ForgeRock AS.
 */

package org.forgerock.opendj.ldap;

import java.util.EventListener;

/**
 * An object that registers to be notified when a connection factory associated
 * with a load-balancer changes state from offline to online or vice-versa.
 * <p>
 * <b>NOTE:</b> load-balancer implementations must ensure that only one event is
 * sent at a time. Event listener implementations should not need to be thread
 * safe.
 */
public interface LoadBalancerEventListener extends EventListener {

    /**
     * Invoked when the load-balancer is unable to obtain a connection from the
     * specified connection factory. The connection factory will be removed from
     * the load-balancer and monitored periodically in order to determine when
     * it is available again, at which point an online notification event will
     * occur.
     *
     * @param factory
     *            The connection factory which has failed.
     * @param error
     *            The last error that occurred.
     */
    void handleConnectionFactoryOffline(ConnectionFactory factory, ErrorResultException error);

    /**
     * Invoked when the load-balancer detects that a previously offline
     * connection factory is available for use again.
     *
     * @param factory
     *            The connection factory which is now available for use.
     */
    void handleConnectionFactoryOnline(ConnectionFactory factory);
}

 opendj-ldap-sdk/src/main/java/org/forgerock/opendj/ldap/RoundRobinLoadBalancingAlgorithm.java

@@ -22,6 +22,7 @@
 *
 *
 *      Copyright 2010 Sun Microsystems, Inc.
 *      Portions copyright 2013 ForgeRock AS.
 */

package org.forgerock.opendj.ldap;
@@ -55,7 +56,6 @@
 */
public final class RoundRobinLoadBalancingAlgorithm extends AbstractLoadBalancingAlgorithm {
    private final int maxIndex;

    private final AtomicInteger nextIndex = new AtomicInteger(-1);

    /**
@@ -66,7 +66,70 @@
     *            The ordered collection of connection factories.
     */
    public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories) {
        super(factories);
        this(factories, null, 1, TimeUnit.SECONDS, null);
    }

    /**
     * Creates a new round robin load balancing algorithm which will monitor
     * offline connection factories every 1 second using the default scheduler.
     *
     * @param factories
     *            The ordered collection of connection factories.
     * @param listener
     *            The event listener which should be notified whenever a
     *            connection factory changes state from online to offline or
     *            vice-versa.
     */
    public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final LoadBalancerEventListener listener) {
        this(factories, listener, 1, TimeUnit.SECONDS, null);
    }

    /**
     * Creates a new round robin load balancing algorithm which will monitor
     * offline connection factories using the specified frequency using the
     * default scheduler.
     *
     * @param factories
     *            The connection factories.
     * @param listener
     *            The event listener which should be notified whenever a
     *            connection factory changes state from online to offline or
     *            vice-versa.
     * @param interval
     *            The interval between attempts to poll offline factories.
     * @param unit
     *            The time unit for the interval between attempts to poll
     *            offline factories.
     */
    public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final LoadBalancerEventListener listener, final long interval, final TimeUnit unit) {
        this(factories, null, interval, unit, null);
    }

    /**
     * Creates a new round robin load balancing algorithm which will monitor
     * offline connection factories using the specified frequency and scheduler.
     *
     * @param factories
     *            The connection factories.
     * @param listener
     *            The event listener which should be notified whenever a
     *            connection factory changes state from online to offline or
     *            vice-versa.
     * @param interval
     *            The interval between attempts to poll offline factories.
     * @param unit
     *            The time unit for the interval between attempts to poll
     *            offline factories.
     * @param scheduler
     *            The scheduler which should for periodically monitoring dead
     *            connection factories to see if they are usable again.
     */
    public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final LoadBalancerEventListener listener, final long interval, final TimeUnit unit,
            final ScheduledExecutorService scheduler) {
        super(factories, listener, interval, unit, scheduler);
        this.maxIndex = factories.size();
    }

@@ -85,8 +148,7 @@
     */
    public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final long interval, final TimeUnit unit) {
        super(factories, interval, unit);
        this.maxIndex = factories.size();
        this(factories, null, interval, unit, null);
    }

    /**
@@ -106,8 +168,7 @@
     */
    public RoundRobinLoadBalancingAlgorithm(final Collection<ConnectionFactory> factories,
            final long interval, final TimeUnit unit, final ScheduledExecutorService scheduler) {
        super(factories, interval, unit, scheduler);
        this.maxIndex = factories.size();
        this(factories, null, interval, unit, scheduler);
    }

    /**

 opendj-ldap-sdk/src/test/java/org/forgerock/opendj/ldap/AbstractLoadBalancingAlgorithmTestCase.java

New file
@@ -0,0 +1,191 @@
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at legal-notices/CDDLv1_0.txt
 * or http://forgerock.org/license/CDDLv1.0.html.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at legal-notices/CDDLv1_0.txt.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information:
 *      Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 *
 *
 *      Copyright 2013 ForgeRock AS
 */
package org.forgerock.opendj.ldap;

import static java.util.Arrays.asList;
import static org.fest.assertions.Assertions.assertThat;
import static org.fest.assertions.Fail.fail;
import static org.forgerock.opendj.ldap.Connections.newLoadBalancer;
import static org.forgerock.opendj.ldap.ErrorResultException.newErrorResult;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.verifyNoMoreInteractions;
import static org.mockito.Mockito.when;

import java.util.concurrent.TimeUnit;
import java.util.logging.Level;

import org.testng.annotations.AfterClass;
import org.testng.annotations.BeforeClass;
import org.testng.annotations.Test;

import com.forgerock.opendj.util.CompletedFutureResult;
import com.forgerock.opendj.util.StaticUtils;

@SuppressWarnings("javadoc")
public class AbstractLoadBalancingAlgorithmTestCase extends SdkTestCase {
    private static ConnectionFactory mockAsync(final ConnectionFactory mock) {
        return new ConnectionFactory() {
            @Override
            public void close() {
                mock.close();
            }

            @Override
            public Connection getConnection() throws ErrorResultException {
                return mock.getConnection();
            }

            @Override
            public FutureResult<Connection> getConnectionAsync(
                    final ResultHandler<? super Connection> handler) {
                try {
                    final Connection connection = mock.getConnection();
                    if (handler != null) {
                        handler.handleResult(connection);
                    }
                    return new CompletedFutureResult<Connection>(connection);
                } catch (final ErrorResultException e) {
                    if (handler != null) {
                        handler.handleErrorResult(e);
                    }
                    return new CompletedFutureResult<Connection>(e);
                }
            }

            @Override
            public String toString() {
                return mock.toString();
            }
        };
    }

    /**
     * Disables logging before the tests.
     */
    @BeforeClass()
    public void disableLogging() {
        StaticUtils.DEBUG_LOG.setLevel(Level.SEVERE);
    }

    /**
     * Re-enable logging after the tests.
     */
    @AfterClass()
    public void enableLogging() {
        StaticUtils.DEBUG_LOG.setLevel(Level.INFO);
    }

    /**
     * Tests fix for OPENDJ-1112: when a load balancer fails completely the
     * connection exception should include the last error that occurred.
     */
    @Test
    public void testFinalFailureExposedAsCause() throws Exception {
        /*
         * Create load-balancer with two failed connection factories.
         */
        final ConnectionFactory first = mock(ConnectionFactory.class, "first");
        final ErrorResultException firstError = newErrorResult(ResultCode.CLIENT_SIDE_SERVER_DOWN);
        when(first.getConnection()).thenThrow(firstError);

        final ConnectionFactory second = mock(ConnectionFactory.class, "second");
        final ErrorResultException secondError = newErrorResult(ResultCode.CLIENT_SIDE_SERVER_DOWN);
        when(second.getConnection()).thenThrow(secondError);

        final ConnectionFactory loadBalancer =
                newLoadBalancer(new RoundRobinLoadBalancingAlgorithm(asList(first, second)));

        /*
         * Belt and braces check to ensure that factory methods don't return
         * same instance and fool this test.
         */
        assertThat(firstError).isNotSameAs(secondError);

        try {
            loadBalancer.getConnection().close();
            fail("Unexpectedly obtained a connection");
        } catch (final ErrorResultException e) {
            assertThat(e.getCause()).isSameAs(secondError);
        } finally {
            loadBalancer.close();
        }
    }

    /**
     * Tests fix for OPENDJ-1112: event listener should be notified when a
     * factory changes state from online to offline or vice versa.
     */
    @Test
    public void testLoadBalancerEventListenerNotification() throws Exception {
        /*
         * Create load-balancer with two failed connection factories and a mock
         * listener and scheduler. The first factory will succeed on the second
         * attempt.
         */
        final ConnectionFactory first = mock(ConnectionFactory.class, "first");
        final ConnectionFactory firstAsync = mockAsync(first);
        final ErrorResultException firstError = newErrorResult(ResultCode.CLIENT_SIDE_SERVER_DOWN);
        when(first.getConnection()).thenThrow(firstError).thenReturn(mock(Connection.class));

        final ConnectionFactory second = mock(ConnectionFactory.class, "second");
        final ConnectionFactory secondAsync = mockAsync(second);
        final ErrorResultException secondError = newErrorResult(ResultCode.CLIENT_SIDE_SERVER_DOWN);
        when(second.getConnection()).thenThrow(secondError);

        final LoadBalancerEventListener listener = mock(LoadBalancerEventListener.class);
        final MockScheduler scheduler = new MockScheduler();
        final ConnectionFactory loadBalancer =
                newLoadBalancer(new RoundRobinLoadBalancingAlgorithm(
                        asList(firstAsync, secondAsync), listener, 1, TimeUnit.SECONDS, scheduler));

        /*
         * Belt and braces check to ensure that factory methods don't return
         * same instance and fool this test.
         */
        assertThat(firstError).isNotSameAs(secondError);

        try {
            loadBalancer.getConnection().close();
            fail("Unexpectedly obtained a connection");
        } catch (final ErrorResultException e) {
            // Check that the event listener has been fired for both factories.
            verify(listener).handleConnectionFactoryOffline(firstAsync, firstError);
            verify(listener).handleConnectionFactoryOffline(secondAsync, secondError);
            verifyNoMoreInteractions(listener);

            // Check that the factories are being monitored.
            assertThat(scheduler.isScheduled()).isTrue();

            // Forcefully run the monitor task and check that the first factory is online.
            scheduler.getCommand().run();
            verify(listener).handleConnectionFactoryOnline(firstAsync);
            verifyNoMoreInteractions(listener);
        } finally {
            loadBalancer.close();
        }
    }
}

 opendj-ldap-sdk/src/test/java/org/forgerock/opendj/ldap/MockScheduler.java

New file
@@ -0,0 +1,226 @@
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at legal-notices/CDDLv1_0.txt
 * or http://forgerock.org/license/CDDLv1.0.html.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at legal-notices/CDDLv1_0.txt.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information:
 *      Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 *
 *
 *      Copyright 2013 ForgeRock AS.
 */
package org.forgerock.opendj.ldap;

import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.Delayed;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * A mock scheduled executor which allows unit tests to directly invoke
 * scheduled tasks without needing to wait.
 */
final class MockScheduler implements ScheduledExecutorService {

    // Saved scheduled task.
    private Runnable command;
    private long delay;
    private boolean isScheduled = false;
    private TimeUnit unit;

    MockScheduler() {
        // Nothing to do.
    }

    @Override
    public boolean awaitTermination(final long timeout, final TimeUnit unit)
            throws InterruptedException {
        // Unused.
        return false;
    }

    @Override
    public void execute(final Runnable command) {
        // Unused.

    }

    @Override
    public <T> List<Future<T>> invokeAll(final Collection<? extends Callable<T>> tasks)
            throws InterruptedException {
        // Unused.
        return null;
    }

    @Override
    public <T> List<Future<T>> invokeAll(final Collection<? extends Callable<T>> tasks,
            final long timeout, final TimeUnit unit) throws InterruptedException {
        // Unused.
        return null;
    }

    @Override
    public <T> T invokeAny(final Collection<? extends Callable<T>> tasks)
            throws InterruptedException, ExecutionException {
        // Unused.
        return null;
    }

    @Override
    public <T> T invokeAny(final Collection<? extends Callable<T>> tasks, final long timeout,
            final TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
        // Unused.
        return null;
    }

    @Override
    public boolean isShutdown() {
        // Unused.
        return false;
    }

    @Override
    public boolean isTerminated() {
        // Unused.
        return false;
    }

    @Override
    public <V> ScheduledFuture<V> schedule(final Callable<V> callable, final long delay,
            final TimeUnit unit) {
        // Unused.
        return null;
    }

    @Override
    public ScheduledFuture<?> schedule(final Runnable command, final long delay, final TimeUnit unit) {
        // Unused.
        return null;
    }

    @Override
    public ScheduledFuture<?> scheduleAtFixedRate(final Runnable command, final long initialDelay,
            final long period, final TimeUnit unit) {
        // Unused.
        return null;
    }

    @Override
    public ScheduledFuture<?> scheduleWithFixedDelay(final Runnable command,
            final long initialDelay, final long delay, final TimeUnit unit) {
        this.command = command;
        this.delay = delay;
        this.unit = unit;
        this.isScheduled = true;
        return new ScheduledFuture<Object>() {
            @Override
            public boolean cancel(final boolean mayInterruptIfRunning) {
                isScheduled = false;
                return true;
            }

            @Override
            public int compareTo(final Delayed o) {
                // Unused.
                return 0;
            }

            @Override
            public Object get() throws InterruptedException, ExecutionException {
                // Unused.
                return null;
            }

            @Override
            public Object get(final long timeout, final TimeUnit unit) throws InterruptedException,
                    ExecutionException, TimeoutException {
                // Unused.
                return null;
            }

            @Override
            public long getDelay(final TimeUnit unit) {
                // Unused.
                return 0;
            }

            @Override
            public boolean isCancelled() {
                return !isScheduled;
            }

            @Override
            public boolean isDone() {
                // Unused.
                return false;
            }

        };
    }

    @Override
    public void shutdown() {
        // Unused.
    }

    @Override
    public List<Runnable> shutdownNow() {
        // Unused.
        return Collections.emptyList();
    }

    @Override
    public <T> Future<T> submit(final Callable<T> task) {
        // Unused.
        return null;
    }

    @Override
    public Future<?> submit(final Runnable task) {
        // Unused.
        return null;
    }

    @Override
    public <T> Future<T> submit(final Runnable task, final T result) {
        // Unused.
        return null;
    }

    Runnable getCommand() {
        return command;
    }

    long getDelay() {
        return delay;
    }

    TimeUnit getUnit() {
        return unit;
    }

    boolean isScheduled() {
        return isScheduled;
    }
}