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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,
* 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
* specific language governing permissions and limitations
* under the License.
*
*/
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;
}
}
}
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