java - 获取每个线程的线程组信息

Question

我有一个线程转储，在这个线程转储中，每个线程都以如下格式显示:

"isThreadCpuTimeSupported": "true",
"getLockOwnerName": null,
"isSuspended": "false",
"stacktrace": "java.base@11.0.5/java.net.PlainSocketImpl.accept0(Native 
"cpuTime": "36359.375",
"userTime": "25828.125",
"threadState": "RUNNABLE",
"id": "1",
"lockName": null,
"threadName": "main",
"isNative": "true"

我的需求是获取每个线程的threadGroup，如何获取？我必须先将它们添加到线程组中吗？我怎么知道它们是否已经是线程组的一部分？在网站上Fastthread.io当我上传线程转储时，它会自动找到线程组，它是如何做到的？

在服务器端我正在做这样的事情来获取线程转储:

ThreadMXBean tmbean = ManagementFactory.getThreadMXBean();
List<HashMap> list = new ArrayList<>();
long[] tids;
ThreadInfo[] tinfos;
tids = tmbean.getAllThreadIds();
tinfos = tmbean.getThreadInfo(tids, Integer.MAX_VALUE);

for (ThreadInfo ti : tinfos) {
    try {
        list.add( printThreadInfo(ti,tmbean,response ));
    } catch (IOException ex) {
        _logger.error("could not call printThreadInfo",ex);
    }
}
...
...

对于每个ti

map.put("threadName", ti.getThreadName());

Answer 1

正如 Sarel Foyerlicht 所提到的，ThreadInfo 没有关于 ThreadGroup 的信息。我们可以利用Thread#getThreadGroup()获取组信息，步骤如下:

1. 获取top ThreadGroup，引用引用答案[1 ]
2. 递归迭代Thread和子ThreadGroup，得到Thread和对应的ThreadGroup的映射，见引用 [ 2 ] Thread 和 ThreadGroup
之间的关系

下面的程序演示了上述步骤。

---

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadInfo;
import java.lang.management.ThreadMXBean;
import java.util.HashMap;
import java.util.Map;

public class ThreadDumpWithGroup {
    public static void main(String args[]) {
        ThreadGroup top = getTopThreadGroup();
        Map<Long, String> threadIdToThreadGroupNameMap = new HashMap<>();
        putThreadIdToThreadGroupNameMap(top, threadIdToThreadGroupNameMap);
        ThreadMXBean threadBean = ManagementFactory.getThreadMXBean();
        long[] threadIds;
        ThreadInfo[] threadInfos;
        threadIds = threadBean.getAllThreadIds();
        threadInfos = threadBean.getThreadInfo(threadIds, Integer.MAX_VALUE);
        for (ThreadInfo threadInfo : threadInfos) {
            // May still be null as there may be new thread after constructing the map.
            String threadGroupName = threadIdToThreadGroupNameMap.get(threadInfo.getThreadId());
            String threadName = threadInfo.getThreadName();
            long threadId = threadInfo.getThreadId();
            System.out.println(
                    String.format("Group:%s, Thread Name:%s, Thread Id:%d", threadGroupName, threadName, threadId));
        }
    }

    /**
     * Result maybe inaccurate, see
     * {@link java.lang.ThreadGroup#enumerate(Thread[], boolean) enumerate}
     * {@link java.lang.ThreadGroup#enumerate(ThreadGroup[], boolean) enumerate}
     **/
    private static void putThreadIdToThreadGroupNameMap(ThreadGroup group,
            Map<Long, String> threadIdToThreadGroupNameMap) {
        Thread[] threads = new Thread[group.activeCount()];
        group.enumerate(threads, false);
        for (Thread thread : threads) {
            if (thread == null) {
                continue;
            }
            threadIdToThreadGroupNameMap.put(thread.getId(), group.getName());
        }

        ThreadGroup[] subGroups = new ThreadGroup[group.activeGroupCount()];
        group.enumerate(subGroups, false);
        for (ThreadGroup subGroup : subGroups) {
            putThreadIdToThreadGroupNameMap(subGroup, threadIdToThreadGroupNameMap);
        }
    }

    private static ThreadGroup getTopThreadGroup() {
        ThreadGroup top = Thread.currentThread().getThreadGroup();
        ThreadGroup parent;
        do {
            parent = top.getParent();
            if (parent != null) {
                top = parent;
            }
        } while (parent != null);
        return top;
    }
}

---

引用文献
Get a list of all threads currently running in Java
Java 101: Understanding Java threads, Part 4: Thread groups, volatility, and thread-local variables
Java Doc Thread Group