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/* Copyright Rupert Smith, 2005 to 2007, all rights reserved. */
/*
* Copyright 2007 Rupert Smith.
*
* Licensed 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 uk.co.thebadgerset.junit.extensions.util;
/**
* SizeOf provides a static method that does its best to return an accurate measure of the total amount of memory used by
* the virtual machine. This is calculated as the total memory available to the VM minus the actual amount used by it.
* Before this measurement is taken the garbage collector is run many times until the used memory calculation stabilizes.
* Generally, this trick works quite well to provide an accurate reading, however, it cannot be relied upon to be totally
* accurate. It is also quite slow.
*
* CRC Card
* Responsibilities Collaborations
* Calculate total memory used.
*
*
* @author Rupert Smith
*/
public class SizeOf
{
/** Holds a reference to the runtime object. */
private static final Runtime RUNTIME = Runtime.getRuntime();
/**
* Makes 4 calls the {@link #runGCTillStable} method.
*/
public static void runGCTillStableSeveralTimes()
{
// It helps to call Runtime.gc() using several method calls.
for (int r = 0; r < 4; ++r)
{
runGCTillStable();
}
}
/**
* Runs the garbage collector until the used memory reading stabilizes. It may run the garbage collector up
* to 500 times.
*/
public static void runGCTillStable()
{
long usedMem1 = usedMemory(), usedMem2 = Long.MAX_VALUE;
for (int i = 0; (usedMem1 < usedMem2) && (i < 500); ++i)
{
RUNTIME.runFinalization();
RUNTIME.gc();
Thread.currentThread().yield();
usedMem2 = usedMem1;
usedMem1 = usedMemory();
}
}
/**
* Runs the garbage collector until the used memory stabilizes and then measures it.
*
* @return The amount of memory used by the virtual machine.
*/
public static long getUsedMemory()
{
runGCTillStableSeveralTimes();
return usedMemory();
}
/**
* Returns the amount of memory used by subtracting the free memory from the total available memory.
*
* @return The amount of memory used.
*/
private static long usedMemory()
{
return RUNTIME.totalMemory() - RUNTIME.freeMemory();
}
}