Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
/**
 * Copyright 2008, David Robert Nadeau, NadeauSoftware.com
 *
 * This file is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 2 of
 * the License, or (at your option) any later version.
 *
 * This file 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this file.  If not, see
 * <a href="http://www.gnu.org/licenses">GNU Licenses</a>.
 */

import java.lang.management.*;

public class Main {
    /**
     * The root thread group saved on the first search for it.
     * The root group doesn't change for the life of the JVM,
     * so once found there is no need to find it again.
     */
    private static ThreadGroup rootThreadGroup = null;

    /**
     * Get a list of all threads.  Since there is always at
     * least one thread, this method never returns null or
     * an empty array.
     *
     * @return      an array of threads
     */
    public static Thread[] getAllThreads() {
        final ThreadGroup root = getRootThreadGroup();
        final ThreadMXBean thbean = ManagementFactory.getThreadMXBean();
        int nAlloc = thbean.getThreadCount();
        int n = 0;
        Thread[] threads = null;
        do {
            nAlloc *= 2;
            threads = new Thread[nAlloc];
            n = root.enumerate(threads, true);
        } while (n == nAlloc);
        return java.util.Arrays.copyOf(threads, n);
    }

    /**
     * Get a list of all threads with a given thread state.
     * Thread states are defined in the Thread.State enum for
     * the Thread class.  Principal thread states include
     * RUNNABLE, WAITING, TIMED_WAITING, and BLOCKED.  An
     * empty array is returned if there are no threads in
     * the chosen state.
     *
     * @param   state   the state to look for
     * @return      an array of threads in that state
     */
    public static Thread[] getAllThreads(final Thread.State state) {
        final Thread[] allThreads = getAllThreads();
        final Thread[] found = new Thread[allThreads.length];
        int nFound = 0;
        for (Thread thread : allThreads)
            if (thread.getState() == state)
                found[nFound++] = thread;
        return java.util.Arrays.copyOf(found, nFound);
    }

    /**
     * Get the root thread group in the thread group tree.
     * Since there is always a root thread group, this
     * method never returns null.
     *
     * @return      the root thread group
     */
    public static ThreadGroup getRootThreadGroup() {
        if (rootThreadGroup != null)
            return rootThreadGroup;

        ThreadGroup tg = Thread.currentThread().getThreadGroup();
        ThreadGroup ptg;
        while ((ptg = tg.getParent()) != null)
            tg = ptg;
        rootThreadGroup = tg;
        return tg;
    }

    /**
     * Get the thread group with the given name.  A null is
     * returned if no such group is found.  If more than one
     * group has the same name, the first one found is returned.
     *
     * @param   name   the thread group name to search for
     * @return      the thread group, or null if not found
     * @throws   NullPointerException
     *          if the name is null
     */
    public static ThreadGroup getThreadGroup(final String name) {
        if (name == null)
            throw new NullPointerException("Null name");
        final ThreadGroup[] groups = getAllThreadGroups();
        for (ThreadGroup group : groups)
            if (group.getName().equals(name))
                return group;
        return null;
    }

    /**
     * Get a list of all thread groups.  Since there is
     * always at least one thread group (the root), this
     * method never returns a null or empty array.
     *
     * @return      an array of thread groups
     */
    public static ThreadGroup[] getAllThreadGroups() {
        final ThreadGroup root = getRootThreadGroup();
        int nAlloc = root.activeGroupCount();
        int n = 0;
        ThreadGroup[] groups = null;
        do {
            nAlloc *= 2;
            groups = new ThreadGroup[nAlloc];
            n = root.enumerate(groups, true);
        } while (n == nAlloc);
        ThreadGroup[] allGroups = new ThreadGroup[n + 1];
        allGroups[0] = root;
        System.arraycopy(groups, 0, allGroups, 1, n);
        return allGroups;
    }
}