test/hotspot/jtreg/gc/arguments/TestSelectDefaultGC.java

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/*
 * @test TestSelectDefaultGC
 * @summary Test selection of GC when no GC option is specified
 * @bug 8068582
 * @key gc
 * @library /test/lib
 * @requires vm.gc=="null"
 * @modules java.base/jdk.internal.misc
 *          java.management
 * @run driver TestSelectDefaultGC
 */

import jdk.test.lib.Platform;
import jdk.test.lib.process.OutputAnalyzer;
import jdk.test.lib.process.ProcessTools;

import java.util.regex.*;

public class TestSelectDefaultGC {
    public static void assertVMOption(OutputAnalyzer output, String option, boolean value) {
        output.shouldMatch(" " + option + " .*=.* " + value + " ");
    }

    public static void testDefaultGC(boolean actAsServer) throws Exception {
        String[] args = new String[] {
          "-XX:" + (actAsServer ? "+" : "-") + "AlwaysActAsServerClassMachine",
          "-XX:" + (actAsServer ? "-" : "+") + "NeverActAsServerClassMachine",
          "-XX:+PrintFlagsFinal",
          "-version"
        };

        // Start VM without specifying GC
        ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(args);
        OutputAnalyzer output = new OutputAnalyzer(pb.start());
        output.shouldHaveExitValue(0);

        final boolean isServer = actAsServer;

        // Verify GC selection
        // G1 is default for server class machines
        assertVMOption(output, "UseG1GC",            isServer);
        // Serial is default for non-server class machines
        assertVMOption(output, "UseSerialGC",        !isServer);
        // CMS is never default
        assertVMOption(output, "UseConcMarkSweepGC", false);
    }

    public static void main(String[] args) throws Exception {
        // Test server class machine
        testDefaultGC(false);

        // Test non-server class machine
        testDefaultGC(true);
    }
}