/*

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

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * 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).

 *

 * You should have received a copy of the GNU General Public License version

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

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

/**

 * @test TestSmallHeap

 * @bug 8067438 8152239

 * @requires vm.gc=="null"

 * @summary Verify that starting the VM with a small heap works

 * @library /test/lib

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

 * @build sun.hotspot.WhiteBox

 * @run driver ClassFileInstaller sun.hotspot.WhiteBox

 * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI TestSmallHeap

 */

/* Note: It would be nice to verify the minimal supported heap size here,

 * but we align the heap size based on the card table size. And the card table

 * size is aligned based on the minimal pages size provided by the os. This

 * means that on most platforms, where the minimal page size is 4k, we get a

 * minimal heap size of 2m but on Solaris/Sparc we have a page size of 8k and

 * get a minimal heap size of 4m. And on platforms where the page size is 64k

 * we get a minimal heap size of 32m. We never use large pages for the card table.

 *

 * There is also no check in the VM for verifying that the maximum heap size

 * is larger than the supported minimal heap size.

 *

 * To work around these behaviors this test uses -Xmx4m but then

 * calculates what the expected heap size should be. The calculation is a

 * simplified version of the code in the VM. We assume that the card table will

 * use one page. Each byte in the card table corresponds to 512 bytes on the heap.

 * So, the expected heap size is page_size * 512.

 *

 * There is no formal requirement for the minimal value of the maximum heap size

 * the VM should support. In most cases the VM could start with -Xmx2m.

 * But with 2m limit GC could be triggered before VM initialization completed.

 * Therefore we start the VM with 4M heap.

 */

import jdk.test.lib.Asserts;

import jdk.test.lib.process.OutputAnalyzer;

import jdk.test.lib.process.ProcessTools;

import java.util.LinkedList;

import sun.hotspot.WhiteBox;

public class TestSmallHeap {

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

        // Do all work in the VM driving the test, the VM

        // with the small heap size should do as little as

        // possible to avoid hitting an OOME.

        WhiteBox wb = WhiteBox.getWhiteBox();

        int pageSize = wb.getVMPageSize();

        int heapBytesPerCard = 512;

        long expectedMaxHeap = pageSize * heapBytesPerCard;

        verifySmallHeapSize("-XX:+UseParallelGC", expectedMaxHeap);

        verifySmallHeapSize("-XX:+UseSerialGC", expectedMaxHeap);

        verifySmallHeapSize("-XX:+UseG1GC", expectedMaxHeap);

        verifySmallHeapSize("-XX:+UseConcMarkSweepGC", expectedMaxHeap);

    }

    private static void verifySmallHeapSize(String gc, long expectedMaxHeap) throws Exception {

        long minMaxHeap = 4 * 1024 * 1024;

        LinkedList<String> vmOptions = new LinkedList<>();

        vmOptions.add(gc);

        vmOptions.add("-Xmx" + minMaxHeap);

        vmOptions.add("-XX:+PrintFlagsFinal");

        vmOptions.add(VerifyHeapSize.class.getName());

        ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(vmOptions.toArray(new String[0]));

        OutputAnalyzer analyzer = new OutputAnalyzer(pb.start());

        analyzer.shouldHaveExitValue(0);

        expectedMaxHeap = Math.max(expectedMaxHeap, minMaxHeap);

        long maxHeapSize = Long.parseLong(analyzer.firstMatch("MaxHeapSize.+=\\s+(\\d+)",1));

        long actualHeapSize = Long.parseLong(analyzer.firstMatch(VerifyHeapSize.actualMsg + "(\\d+)",1));

        Asserts.assertEQ(maxHeapSize, expectedMaxHeap);

        Asserts.assertLessThanOrEqual(actualHeapSize, maxHeapSize);

    }

}

class VerifyHeapSize {

    public static final String actualMsg = "Actual heap size: ";

    public static void main(String args[]) {

        // Avoid string concatenation

        System.out.print(actualMsg);

        System.out.println(Runtime.getRuntime().maxMemory());

    }

}