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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

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 * 2 along with this work; if not, write to the Free Software Foundation,

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/*

 * @test TestNoEagerReclaimOfHumongousRegions

 * @bug 8139424

 * @summary Test to check that a live humongous object is not eagerly reclaimed. This is a regression test for

 *          8139424 and the test will crash if an eager reclaim occur. The test is not 100% deterministic and

 *          might pass even if there are problems in the code, but it will never crash unless there is a problem.

 * @requires vm.gc.G1

 * @key gc

 * @library /test/lib

 * @modules java.base/jdk.internal.misc

 * @build sun.hotspot.WhiteBox

 * @run main ClassFileInstaller sun.hotspot.WhiteBox

 *                              sun.hotspot.WhiteBox$WhiteBoxPermission

 * @run main/othervm -Xbootclasspath/a:. -Xlog:gc,gc+humongous=debug -XX:+UseG1GC -XX:MaxTenuringThreshold=0 -XX:G1RSetSparseRegionEntries=32 -XX:G1HeapRegionSize=1m -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI TestNoEagerReclaimOfHumongousRegions

 */

import java.util.LinkedList;

import sun.hotspot.WhiteBox;

public class TestNoEagerReclaimOfHumongousRegions {

    // Helper class to keep reference to humongous byte[].

    static class LargeRef {

        private byte[] _ref;

        LargeRef(byte[] ref) {

            _ref = ref;

        }

        byte[] ref() { return _ref; }

    }

    static LargeRef humongous_reference_holder;

    public static void main(String[] args) throws InterruptedException{

        WhiteBox wb = WhiteBox.getWhiteBox();

        LinkedList<Object> garbageAndRefList = new LinkedList<Object>();

        // Creating a 1M large byte array. Since the test specifies the heap

        // region size to be 1m this will be a humongous object. We then

        // store a pointer to the array in the static object to keep it live

        // during the whole test.

        humongous_reference_holder = new LargeRef(new byte[1 * 1024 * 1024]);

        // Create some garbage and a reference to the humongous object each round.

        for (int i = 0; i < 32; i++) {

            garbageAndRefList.add(new byte[400*1000]);

            garbageAndRefList.add(new LargeRef(humongous_reference_holder.ref()));

            // Promote to old, goal is to get rem-set entries for the humongous

            // object from different regions. The test specifies MaxTenuringThreshold=0,

            // this will make sure we get objects promoted to old at once.

            wb.youngGC();

        }

        // Clear the garbage and reference list.

        garbageAndRefList.clear();

        // Run a concurrent mark cycle to mark all references but the static one as dead.

        wb.g1StartConcMarkCycle();

        while (wb.g1InConcurrentMark()) {

            Thread.sleep(100);

        }

        // Run a young collection to make sure humongous object still can't be eagerly reclaimed.

        wb.youngGC();

        // Will crash/assert if humongous object has been reclaimed.

        wb.fullGC();

    }

}