获得当前所有的线程

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[] slackList = new Thread[estimatedSize];

  // 获取根线程组的所有线程

  int actualSize = topGroup.enumerate(slackList);

  // copy into a list that is the exact size

  Thread[] list = new Thread[actualSize];

  System.arraycopy(slackList, 0, list, 0, actualSize);

  return list;

 }