test/gc_implementation/g1/TestNoEagerReclaimOfHumongousRegions.java

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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" | vm.gc=="null"
 * @key gc
 * @library /testlibrary /testlibrary/whitebox
 * @modules java.base/sun.misc
 * @build TestNoEagerReclaimOfHumongousRegions
 * @run main ClassFileInstaller sun.hotspot.WhiteBox
 *                              sun.hotspot.WhiteBox$WhiteBoxPermission
 * @run main/othervm -Xbootclasspath/a:. -XX:+PrintGC -XX:+UseG1GC -XX:MaxTenuringThreshold=0 -XX:G1RSetSparseRegionEntries=32 -XX:G1HeapRegionSize=1m -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -XX:+UnlockExperimentalVMOptions -XX:+G1TraceEagerReclaimHumongousObjects 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();
    }
}