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 *
 * Licensed to the Apache Software Foundation (ASF) under one
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 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
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 */
package org.apache.qpid.test.framework.clocksynch;

/**
 * ClockSynchronizer provides an interface through which two nodes may synchronize their clocks. It is expected that one
 * node will act as the reference clock, to which no delta need be applied, and the other node will act as the slave,
 * and which must apply a delta to its local clock to get a clock synchronized with the reference.
 *
 * <p/>The slave side will initiate the computation of a clock delta by calling the {@link #synch} method. This method
 * will not return until the delta has been computed, at which point there is a method to return its value, as well as
 * an estimate of the likely error (usually one standard deviation), in the synchronization. For convenience there is a
 * {@link #nanoTime} method to return the value of System.nanoTime() with the delta added in.
 *
 * <p/><table id="crc"><caption>CRC Card</caption>
 * <tr><th> Responsibilities <th> Collaborations
 * <tr><td> Trigger a clock synchronziation.
 * <tr><td> Compute a clock delta to apply to the local clock.
 * <tr><td> Estimate the error in the synchronzation.
 * </table>
 */
public interface ClockSynchronizer
{
    /**
     * The slave side should call this to copute a clock delta with the reference.
     *
     * @throws ClockSynchFailureException If synchronization cannot be achieved.
     */
    public void synch() throws ClockSynchFailureException;

    /**
     * Gets the clock delta in nano seconds.
     *
     * @return The clock delta in nano seconds.
     */
    public long getDelta();

    /**
     * Gets an estimate of the clock error in nan seconds.
     *
     * @return An estimate of the clock error in nan seconds.
     */
    public long getEpsilon();

    /**
     * Gets the local clock time with any computed delta added in.
     *
     * @return The local clock time with any computed delta added in.
     */
    public long nanoTime();
}
