RC9/qpid/java/junit-toolkit/src/main/org/apache/qpid/junit/extensions/BaseThrottle.java

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 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * 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,
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 * KIND, either express or implied.  See the License for the
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package org.apache.qpid.junit.extensions;

/**
 * Provides a base implementation of the non-waiting throttle checking method, using the system nano timer.
 *
 * <p/><table id="crc"><caption>CRC Card</caption>
 * <tr><th> Responsibilities <th> Collaborations
 * <tr><td> Check against a throttle speed without waiting.
 * </table>
 *
 * @author Rupert Smith
 */
public abstract class BaseThrottle implements Throttle
{
    /** Holds the length of a single cycle in nano seconds. */
    protected long cycleTimeNanos;

    /** Holds the time of the last succesfull call to the check method. */
    private long lastCheckTimeNanos;

    /** Flag used to detect the first call to the {@link #checkThrottle()} method. */
    boolean firstCheckCall = true;

    /**
     * Flag used to detect the first call to the {@link #throttle()} method. Zero or negative start time cannot be
     * relied on to detect this as System.nanoTime can return zero or negative values.
     */
    boolean firstCall = true;

    /**
     * Specifies the throttling rate in operations per second. This must be called with with a value, the inverse
     * of which is a measurement in nano seconds, such that the number of nano seconds do not overflow a long integer.
     * The value must also be larger than zero.
     *
     * @param hertz The throttling rate in cycles per second.
     */
    public void setRate(float hertz)
    {
        // Check that the argument is above zero.
        if (hertz <= 0.0f)
        {
            throw new IllegalArgumentException("The throttle rate must be above zero.");
        }

        // Calculate the cycle time.
        cycleTimeNanos = (long) (1000000000f / hertz);

        // Reset the first pass flag.
        firstCall = false;
        firstCheckCall = false;
    }

    /**
     * Checks but does not enforce the throttle rate. When this method is called, it checks if a length of time greater
     * than that equal to the inverse of the throttling rate has passed since it was last called and returned <tt>true</tt>
     *
     * @return <tt>true</tt> if a length of time greater than that equal to the inverse of the throttling rate has
     *         passed since this method was last called and returned <tt>true</tt>, <tt>false</tt> otherwise. The very
     *         first time this method is called on a throttle, it returns <tt>true</tt> as the base case to the above
     *         self-referential definition.
     */
    public boolean checkThrottle()
    {
        long now = System.nanoTime();

        if ((now > (cycleTimeNanos + lastCheckTimeNanos)) || firstCheckCall)
        {
            firstCheckCall = false;
            lastCheckTimeNanos = now;

            return true;
        }
        else
        {
            return false;
        }
    }
}