获取Java VM中当前运行的所有线程

    /**
     *  获取Java VM中当前运行的所有线程
     * @return
     */
    public static Thread[] findAllThreads() {
        ThreadGroup group = Thread.currentThread().getThreadGroup();
        ThreadGroup topGroup = group;
        // 遍历线程组树，获取根线程组
        while (group != null) {
            topGroup = group;
            group = group.getParent();
        }
        // 激活的线程数加倍
        int estimatedSize = topGroup.activeCount() * 2;
        Thread[] slacks = new Thread[estimatedSize];
         //获取根线程组的所有线程
        int actualSize = topGroup.enumerate(slacks);
        Thread[] threads = new Thread[actualSize];
        System.arraycopy(slacks, 0, threads, 0, actualSize);
        return threads;
    }