ThreadLists.java

/*
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 *
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 * 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
 * @bug 5047639
 * @summary Check that the "java-level" APIs provide a consistent view of
 *          the thread list
 */
import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;
import java.util.Map;

public class ThreadLists {
    public static void main(String args[]) {

        // Bug id : JDK-8151797
        // Use a lambda expression so that call-site cleaner thread is started
        Runnable printLambda = () -> {System.out.println("Starting Test");};
        printLambda.run();

        // get top-level thread group
        ThreadGroup top = Thread.currentThread().getThreadGroup();
        ThreadGroup parent;
        do {
            parent = top.getParent();
            if (parent != null) top = parent;
        } while (parent != null);

        // get the thread count
        int activeCount = top.activeCount();

        Map<Thread, StackTraceElement[]> stackTraces = Thread.getAllStackTraces();

        ThreadMXBean threadBean = ManagementFactory.getThreadMXBean();
        int threadCount = threadBean.getThreadCount();
        long[] threadIds = threadBean.getAllThreadIds();

        System.out.println("ThreadGroup: " + activeCount + " active thread(s)");
        System.out.println("Thread: " + stackTraces.size() + " stack trace(s) returned");
        System.out.println("ThreadMXBean: " + threadCount + " live threads(s)");
        System.out.println("ThreadMXBean: " + threadIds.length + " thread Id(s)");

        // check results are consistent
        boolean failed = false;
        if (activeCount != stackTraces.size()) failed = true;
        if (activeCount != threadCount) failed = true;
        if (activeCount != threadIds.length) failed = true;

        if (failed) {
            throw new RuntimeException("inconsistent results");
        }
    }
}