《Java 并发编程·性能诊断与事故》6.2 pinning 的诊断与消除

--- 默认 profile.jfc（阈值 20 ms）---
wall=10ms
 jdk.VirtualThreadPinned                     0             0

--- 命令行 override threshold=0ms ---
wall=8ms
 jdk.VirtualThreadPinned                     5           355

  duration = 7.51 ms
  pinnedReason = "VM call to Pin5ms$C1.<clinit> on stack"
  eventThread = "short-pin-1" (javaThreadId = 32, virtual)

# 写法一：命令行直接 override 事件设置
java -XX:StartFlightRecording=filename=/tmp/pin.jfr,dumponexit=true,\
jdk.VirtualThreadPinned#threshold=0ms -cp out YourMain

# 写法二：先生成一份阈值为 0 的配置，再引用它（团队内复用最方便）
jfr configure --input "$JAVA_HOME/lib/jfr/profile.jfc" \
  --output /tmp/custom.jfc jdk.VirtualThreadPinned#threshold=0ms
java -XX:StartFlightRecording=filename=/tmp/pin.jfr,settings=/tmp/custom.jfc,dumponexit=true \
  -cp out YourMain

# 写法三：对已经跑起来的进程在线抓 10 秒
jcmd <pid> JFR.start name=pin settings=profile \
  jdk.VirtualThreadPinned#threshold=0ms duration=10s filename=/tmp/pin.jfr

<event name="jdk.VirtualThreadPinned">
  <setting name="enabled">true</setting>
  <setting name="stackTrace">true</setting>
  <setting name="threshold">0 ms</setting>

import java.util.concurrent.atomic.AtomicLong;

/** 自检 + 对照：2 次类初始化 pin，96 次 synchronized+sleep，379 次 Object.wait。 */
public final class MixedEvidence {

    static final Object MON = new Object();
    static final Object WAIT_MON = new Object();
    static final AtomicLong SYNC = new AtomicLong(), WAIT = new AtomicLong();
    static volatile boolean stop;

    static final class InitA { static final int V; static { sleep(5); V = 1; } static int v() { return V; } }
    static final class InitB { static final int V; static { sleep(5); V = 2; } static int v() { return V; } }

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

    public static void main(String[] args) throws Exception {
        for (int i = 0; i < 4; i++) {
            Thread.ofVirtual().name("sync-" + i).start(() -> {
                while (!stop) { synchronized (MON) { sleep(100); SYNC.incrementAndGet(); } }
            });
            Thread.ofVirtual().name("wait-" + i).start(() -> {
                while (!stop) {
                    synchronized (WAIT_MON) {
                        try { WAIT_MON.wait(100); }
                        catch (InterruptedException e) { Thread.currentThread().interrupt(); return; }
                        WAIT.incrementAndGet();
                    }
                }
            });
        }
        Thread.ofVirtual().name("self-check").start(() -> {
            sleep(1000);
            InitA.v();                       // 第 1 次自检 pin
            sleep(4000);
            InitB.v();                       // 第 2 次自检 pin
        });
        Thread.sleep(10_000);
        stop = true;
        Thread.sleep(300);
        System.out.printf("synchronized+sleep=%d, synchronized+wait=%d%n", SYNC.get(), WAIT.get());
    }
}

synchronized+sleep 次数=96, synchronized+wait 次数=379
 jdk.VirtualThreadPinned                    87          4924

wall=422ms  (16 个 200ms 的 <clinit>；10 载体若全 pin 需≈400ms, 不 pin≈200ms)
 jdk.VirtualThreadPinned                    16         1228
  duration = 202 ms
  pinnedReason = "VM call to ClinitStorm$C2.<clinit> on stack"
  eventThread = "clinit-2" (javaThreadId = 34, virtual)

  duration = 107 ms
  blockingOperation = "Object.wait"
  pinnedReason = "Native or VM frame on stack"
  carrierThread = "ForkJoinPool-1-worker-4" (javaThreadId = 42)
  eventThread = "wait-3" (javaThreadId = 39, virtual)
  stackTrace = [
    java.lang.Object.wait0(long)
    java.lang.Object.wait(long) line: 382
    MixedEvidence.lambda$main$1() line: 38
    java.lang.VirtualThread.run(Runnable) line: 460

jni starvation N=8 block=200ms wall=1690ms

  duration = 310 ms
  blockingOperation = "LockSupport.park"
  pinnedReason = "Native or VM frame on stack"
  carrierThread = "ForkJoinPool-1-worker-1" (javaThreadId = 31)
  eventThread = "jni-callback-park" (javaThreadId = 30, virtual)

package com.plume.conc.ops;

import jdk.jfr.Recording;
import jdk.jfr.consumer.RecordedEvent;
import jdk.jfr.consumer.RecordingFile;
import java.nio.file.Path;
import java.time.Duration;
import java.util.HashMap;
import java.util.Map;

/**
 * 开一段只收 VirtualThreadPinned 的录制，按 pinnedReason 聚合。
 * 注意：必须显式把阈值设成 0，否则短 pin 全被过滤。
 */
public final class PinWatch {

    public static Map<String, Long> sample(Path out, Duration d) throws Exception {
        try (Recording r = new Recording()) {
            r.enable("jdk.VirtualThreadPinned").withThreshold(Duration.ZERO).withStackTrace();
            r.start();
            Thread.sleep(d.toMillis());
            r.stop();
            r.dump(out);

            Map<String, Long> byReason = new HashMap<>();
            try (RecordingFile file = new RecordingFile(out)) {
                while (file.hasMoreEvents()) {
                    RecordedEvent e = file.readEvent();
                    if (!e.getEventType().getName().equals("jdk.VirtualThreadPinned")) {
                        continue;
                    }
                    String reason = e.getString("pinnedReason");
                    byReason.merge(reason == null ? "<null>" : reason, 1L, Long::sum);
                }
            }
            return byReason;
        }
    }
}