《Java 虚拟机原理与性能调优》8.1 线程栈与转储：从 jstack 到 JSON 线程容器

"libraryd-worker-0" #25 [26627] daemon prio=5 os_prio=31 cpu=0.79ms elapsed=223.45s
   java.lang.Thread.State: WAITING (parking)
	at jdk.internal.misc.Unsafe.park(java.base@25.0.5/Native Method)
	- parking to wait for  <0x0000000424c18ae8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
	at java.util.concurrent.locks.LockSupport.park(java.base@25.0.5/LockSupport.java:369)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(java.base@25.0.5/AbstractQueuedSynchronizer.java:520)
	at java.util.concurrent.ForkJoinPool.unmanagedBlock(java.base@25.0.5/ForkJoinPool.java:4364)
	at java.util.concurrent.ForkJoinPool.managedBlock(java.base@25.0.5/ForkJoinPool.java:4310)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(java.base@25.0.5/AbstractQueuedSynchronizer.java:1752)
	at java.util.concurrent.LinkedBlockingQueue.take(java.base@25.0.5/LinkedBlockingQueue.java:435)

public class DeadlockDemo {
    private static final Object BOOK_A = new Object();
    private static final Object BOOK_B = new Object();

    public static void main(String[] args) throws Exception {
        Thread t1 = new Thread(() -> {
            synchronized (BOOK_A) {
                sleep(200);
                synchronized (BOOK_B) { System.out.println("t1 got both"); }
            }
        }, "loan-desk-A");
        Thread t2 = new Thread(() -> {
            synchronized (BOOK_B) {
                sleep(200);
                synchronized (BOOK_A) { System.out.println("t2 got both"); }
            }
        }, "loan-desk-B");
        t1.start();
        t2.start();
        t1.join();
        t2.join();
    }

    static void sleep(long ms) {
        try { Thread.sleep(ms); } catch (InterruptedException e) { Thread.currentThread().interrupt(); }
    }
}

Found one Java-level deadlock:
=============================
"loan-desk-A":
  waiting to lock monitor 0x0000000cad04a4c0 (object 0x000000035fc18210, a java.lang.Object),
  which is held by "loan-desk-B"

"loan-desk-B":
  waiting to lock monitor 0x0000000cad04a3e0 (object 0x000000035fc18200, a java.lang.Object),
  which is held by "loan-desk-A"

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;

public class ThreadDumpDemo {
    public static void main(String[] args) throws Exception {
        BlockingQueue<String> queue = new LinkedBlockingQueue<>();
        for (int i = 0; i < 4; i++) {
            Thread worker = new Thread(() -> {
                try {
                    while (true) { queue.take(); }
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            }, "libraryd-worker-" + i);
            worker.setDaemon(true);
            worker.start();
        }

        var executor = Executors.newVirtualThreadPerTaskExecutor();
        for (int i = 0; i < 1000; i++) {
            executor.submit(() -> {
                try { Thread.sleep(600_000); } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            });
        }
        System.out.println("pid=" + ProcessHandle.current().pid());
        Thread.sleep(600_000);
        executor.close();
    }
}

jcmd <pid> Thread.print | grep -c 'loan-vt-'

0

jcmd <pid> Thread.dump_to_file -format=json /tmp/vol4-d/threads/threads2.json

Created /tmp/vol4-d/threads/threads2.json

import json
d = json.load(open("threads2.json"))
for c in d["threadDump"]["threadContainers"]:
    th = c.get("threads", [])
    print(c["container"], len(th), sum(1 for t in th if t.get("virtual")))

<root>                                             12     0
ForkJoinPool.commonPool/...                         0     0
java.util.concurrent.ThreadPerTaskExecutor@7f7351e3 1000 1000
ForkJoinPool-1/...                                  11     0
java.util.concurrent.ThreadPoolExecutor@266474c2     0     0
total threads: 1023

name: ""  state: TIMED_WAITING  virtual: true
stack: java.base/java.lang.VirtualThread.parkNanos(VirtualThread.java:787)
       java.base/java.lang.VirtualThread.sleepNanos(VirtualThread.java:983)
       java.base/java.lang.Thread.sleepNanos(Thread.java:507)

for i in 1 2 3; do
  jcmd "$pid" Thread.print > "/tmp/libraryd-threads-$i.txt"
  jcmd "$pid" Thread.dump_to_file -format=json "/tmp/libraryd-threads-$i.json"
  sleep 5
done

/tmp/vol4-d/threads/threads2.json exists, use -overwrite to overwrite

package com.plume.library.web;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;

public final class RequestWorkers {

    public static Thread start(int index, BlockingQueue<Long> returnedLoans) {
        Thread worker = new Thread(() -> {
            while (!Thread.currentThread().isInterrupted()) {
                try {
                    Long loanId = returnedLoans.poll(1, TimeUnit.SECONDS);
                    if (loanId != null) {
                        System.out.println("processed loan " + loanId);
                    }
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            }
        }, "libraryd-worker-" + index);
        worker.setDaemon(true);
        worker.start();
        return worker;
    }
}

try (var executor = Executors.newThreadPerTaskExecutor(
        Thread.ofVirtual().name("http-", 0).factory())) {
    executor.submit(() -> handle(request));
}

#!/bin/sh
set -eu
pid="${1:?usage: thread-dump.sh <pid> <out-dir>}"
out="${2:?usage: thread-dump.sh <pid> <out-dir>}"
stamp="$(date +%Y%m%d-%H%M%S)"
mkdir -p "$out"
jcmd "$pid" Thread.print > "$out/threads-$stamp.txt"
jcmd "$pid" Thread.dump_to_file -format=json "$out/threads-$stamp.json"
jcmd "$pid" GC.class_histogram > "$out/histogram-$stamp.txt"