176e1beb01
Added the test which checks that Humongous objects allocation threshold works as expected Reviewed-by: tschatzl, dfazunen
59 lines
2.3 KiB
Java
59 lines
2.3 KiB
Java
/*
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* Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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package gc.g1.humongousObjects;
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import sun.hotspot.WhiteBox;
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public class Helpers {
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// In case of 128 byte padding
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private static final int MAX_PADDING_SIZE = 128;
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/**
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* Detects amount of extra bytes required to allocate a byte array.
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* Allocating a byte[n] array takes more then just n bytes in the heap.
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* Extra bytes are required to store object reference and the length.
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* This amount depends on bitness and other factors.
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*
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* @return byte[] memory overhead
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*/
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public static int detectByteArrayAllocationOverhead() {
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WhiteBox whiteBox = WhiteBox.getWhiteBox();
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int zeroLengthByteArraySize = (int) whiteBox.getObjectSize(new byte[0]);
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// Since we do not know is there any padding in zeroLengthByteArraySize we cannot just take byte[0] size as overhead
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for (int i = 1; i < MAX_PADDING_SIZE + 1; ++i) {
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int realAllocationSize = (int) whiteBox.getObjectSize(new byte[i]);
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if (realAllocationSize != zeroLengthByteArraySize) {
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// It means we did not have any padding on previous step
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return zeroLengthByteArraySize - (i - 1);
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}
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}
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throw new Error("We cannot find byte[] memory overhead - should not reach here");
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}
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}
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