* @requires vm.gc=="null" | vm.gc=="G1"

 * @library /testlibrary

 * @run main TestG1HeapRegionSize

import java.util.regex.Matcher;

import java.util.regex.Pattern;

import java.util.ArrayList;

import java.util.Arrays;

import jdk.test.lib.*;

  private static void checkG1HeapRegionSize(String[] flags, int expectedValue, int exitValue) throws Exception {

    ArrayList<String> flagList = new ArrayList<String>();

    flagList.addAll(Arrays.asList(flags));

    flagList.add("-XX:+UseG1GC");

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

    flagList.add("-version");

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

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

    output.shouldHaveExitValue(exitValue);

    if (exitValue == 0) {

      String stdout = output.getStdout();

      int flagValue = getFlagValue("G1HeapRegionSize", stdout);

      if (flagValue != expectedValue) {

        throw new RuntimeException("Wrong value for G1HeapRegionSize. Expected " + expectedValue + " but got " + flagValue);

      }

  private static int getFlagValue(String flag, String where) {

    Matcher m = Pattern.compile(flag + "\\s+:?=\\s+\\d+").matcher(where);

    if (!m.find()) {

      throw new RuntimeException("Could not find value for flag " + flag + " in output string");

    String match = m.group();

    return Integer.parseInt(match.substring(match.lastIndexOf(" ") + 1, match.length()));

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

    final int M = 1024 * 1024;

    checkG1HeapRegionSize(new String[] { "-Xmx64m"   /* default is 1m */        },  1*M, 0);

    checkG1HeapRegionSize(new String[] { "-Xmx64m",  "-XX:G1HeapRegionSize=2m"  },  2*M, 0);

    checkG1HeapRegionSize(new String[] { "-Xmx64m",  "-XX:G1HeapRegionSize=3m"  },  2*M, 0);

    checkG1HeapRegionSize(new String[] { "-Xmx256m", "-XX:G1HeapRegionSize=32m" }, 32*M, 0);

    checkG1HeapRegionSize(new String[] { "-Xmx256m", "-XX:G1HeapRegionSize=64m" }, 32*M, 1);

  }