Java JFR 民间指南 - 事件详解 - jdk.ThreadAllocationStatistics（上）

package com.github.hashjang.jfr.test;
import com.sun.management.ThreadMXBean;
import jdk.jfr.Recording;
import jdk.jfr.consumer.RecordedEvent;
import jdk.jfr.consumer.RecordedThread;
import jdk.jfr.consumer.RecordingFile;
import sun.hotspot.WhiteBox;
import java.io.File;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.nio.file.Path;
import java.time.Duration;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;
public class TestThreadAllocationStatistics {
    private static String EVENT_NAME = "jdk.ThreadAllocationStatistics";
    //50ms采集一次
    private static long eventPeriodMillis = 50;
    //对于字节数组对象头占用16字节
    private static final int BYTE_ARRAY_OVERHEAD = 16;
    //我们要测试的对象大小是1kb
    private static final int OBJECT_SIZE = 1024;
    public static void main(String[] args) throws IOException {
        Recording recording = new Recording();
        recording.enable(EVENT_NAME).withPeriod(Duration.ofMillis(eventPeriodMillis));
        recording.start();
        //使用 WhiteBox 执行 FullGC，清除干扰
        WhiteBox whiteBox = WhiteBox.getWhiteBox();
        whiteBox.fullGC();
        Allocator allocators[] = new Allocator[4];
        CountDownLatch allocationsDoneLatch = new CountDownLatch(allocators.length);
        for (int i = 0; i < allocators.length; i++) {
            allocators[i] = new Allocator(allocationsDoneLatch, OBJECT_SIZE * (i + 1) - BYTE_ARRAY_OVERHEAD);
            allocators[i].setDaemon(true);
            allocators[i].start();
        }
        Map<Long, Allocator> map = Arrays.stream(allocators).collect(Collectors.toMap(Thread::getId, v -> v));
        Map<Long, Long> threadAllocatedMap = new HashMap<>();
        try {
            allocationsDoneLatch.await();
            //再等待一段时间让定时采集 jdk.ThreadAllocationStatistics 采集到最新的
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        recording.stop();
        Path path = new File(new File(".").getAbsolutePath(), "recording-" + recording.getId() + "-pid" + ProcessHandle.current().pid() + ".jfr").toPath();
        recording.dump(path);
        for (RecordedEvent event : RecordingFile.readAllEvents(path)) {
            if (!EVENT_NAME.equals(event.getEventType().getName())) {
                continue;
            }
            long javaThreadId = ((RecordedThread) event.getValue("thread")).getJavaThreadId();
            if (map.containsKey(javaThreadId)) {
                //事件是时间有序的（采集时间比较短），所以放入的最后一个就是采集到的线程最终的分配大小
                threadAllocatedMap.put(javaThreadId, event.getLong("allocated"));
                System.out.println(event);
            }
        }
        map.forEach((id, thread) -> {
            System.out.println("Thread " + id + " allocated(from JMX): " + thread.totalAllocated + "; allocated(from jdk.ThreadAllocationStatistics): " + threadAllocatedMap.get(id));
        });
    }
    public static class Allocator extends Thread {
        private volatile long totalAllocated = -1;
        private final int allocationSize;
        public byte[] buffer;
        private final CountDownLatch allocationsDoneLatch;
        public Allocator(CountDownLatch allocationsDoneLatch, int allocationSize) {
            this.allocationsDoneLatch = allocationsDoneLatch;
            this.allocationSize = allocationSize;
        }
        @Override
        public void run() {
            for (int batches = 0; batches < 100; batches++) {
                for (int i = 0; i < 1024; i++) {
                    buffer = new byte[allocationSize];
                }
                try {
                    //期望每个采集周期之间的分配次数为 5
                    Thread.sleep(eventPeriodMillis / 5);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            //获取当前线程分配的对象大小
            totalAllocated = getThreadAllocatedBytes();
            allocationsDoneLatch.countDown();
            //设置线程为守护线程，等待主线程结束之后会自动结束
            //这里进入死循环是因为防止定时采集 jdk.ThreadAllocationStatistics 事件的时候采集不到
            while (true) {
                Thread.yield();
            }
        }
        private long getThreadAllocatedBytes() {
            ThreadMXBean bean = (ThreadMXBean) ManagementFactory.getThreadMXBean();
            return bean.getThreadAllocatedBytes(Thread.currentThread().getId());
        }
    }
}

-Xbootclasspath/a:D:\github\jfr-spring-all\jdk-white-box\target\jdk-white-box-17.0-SNAPSHOT.jar  -Xms512m