全网最硬核 JVM TLAB 分析(额外加菜) 8. 通过 JFR 监控 TLAB

  false
  true



  false
  true

//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100kb
private static final int OBJECT_SIZE = 100 * 1024;
//需要使用静态field，而不是方法内本地变量，否则编译后循环内的new byte[]全部会被省略，只剩最后一次的
public static byte[] tmp;

public static void main(String[] args) throws Exception {
    WhiteBox whiteBox = WhiteBox.getWhiteBox();
    //初始化 JFR 记录
    Recording recording = new Recording();
    //启用 jdk.ObjectAllocationOutsideTLAB 事件监控
    recording.enable("jdk.ObjectAllocationOutsideTLAB");
    recording.enable("jdk.ObjectAllocationInNewTLAB");
    // JFR 记录启动
    recording.start();

    //强制 fullGC 防止接下来程序发生 GC
    //同时可以区分出初始化带来的其他线程的TLAB相关的日志
    whiteBox.fullGC();
    //分配对象，大小1KB
    for (int i = 0; i < 512; ++i) {
        tmp = new byte[OBJECT_SIZE - BYTE_ARRAY_OVERHEAD];
    }
    //强制 fullGC，回收所有 TLAB
    whiteBox.fullGC();
    //分配对象，大小100KB
    for (int i = 0; i < 200; ++i) {
        tmp = new byte[OBJECT_SIZE * 100 - BYTE_ARRAY_OVERHEAD];
    }
    whiteBox.fullGC();

    //将 JFR 记录 dump 到一个文件
    Path path = new File(new File(".").getAbsolutePath(), "recording-" + recording.getId() + "-pid" + ProcessHandle.current().pid() + ".jfr").toPath();
    recording.dump(path);
    int countOf1KBObjectAllocationInNewTLAB = 0;
    int countOf100KBObjectAllocationInNewTLAB = 0;
    int countOf1KBObjectAllocationOutsideTLAB = 0;
    int countOf100KBObjectAllocationOutsideTLAB = 0;
    //读取文件中的所有 JFR 事件
    for (RecordedEvent event : RecordingFile.readAllEvents(path)) {
        //获取分配的对象的类型
        String className = event.getString("objectClass.name");

        if (
            //确保分配类型是 byte[]
                BYTE_ARRAY_CLASS_NAME.equalsIgnoreCase(className)
        ) {
            RecordedFrame recordedFrame = event.getStackTrace().getFrames().get(0);
            //同时必须是咱们这里的main方法分配的对象，并且是Java堆栈中的main方法
            if (recordedFrame.isJavaFrame()
                    && "main".equalsIgnoreCase(recordedFrame.getMethod().getName())
            ) {
                //获取分配对象大小
                long allocationSize = event.getLong("allocationSize");
                //统计各种事件个数
                if ("jdk.ObjectAllocationOutsideTLAB".equalsIgnoreCase(event.getEventType().getName())) {
                    if (allocationSize == 102400) {
                        countOf100KBObjectAllocationOutsideTLAB++;
                    } else if (allocationSize == 1024) {
                        countOf1KBObjectAllocationOutsideTLAB++;
                    }
                } else if ("jdk.ObjectAllocationInNewTLAB".equalsIgnoreCase(event.getEventType().getName())) {
                    if (allocationSize == 102400) {
                        countOf100KBObjectAllocationInNewTLAB++;
                    } else if (allocationSize == 1024) {
                        countOf1KBObjectAllocationInNewTLAB++;
                    }
                } else {
                    throw new Exception("unexpected size of TLAB event");
                }
                System.out.println(event);
            }
        }
    }
    System.out.println("countOf1KBObjectAllocationInNewTLAB: " + countOf1KBObjectAllocationInNewTLAB);
    System.out.println("countOf100KBObjectAllocationInNewTLAB: " + countOf100KBObjectAllocationInNewTLAB);
    System.out.println("countOf1KBObjectAllocationOutsideTLAB: " + countOf1KBObjectAllocationOutsideTLAB);
    System.out.println("countOf100KBObjectAllocationOutsideTLAB: " + countOf100KBObjectAllocationOutsideTLAB);
    //阻塞程序，保证所有日志输出完
    Thread.currentThread().join();
}

//省略其他事件的详细信息，这里每种挑一个展示
jdk.ObjectAllocationInNewTLAB {
  startTime = 13:07:51.681
  objectClass = byte[] (classLoader = bootstrap)
  allocationSize = 1.0 kB
  tlabSize = 478.2 kB
  eventThread = "main" (javaThreadId = 1)
  stackTrace = [
    com.github.hashjang.jfr.test.TestAllocOutsideTLAB.main(String[]) line: 96
  ]
}


jdk.ObjectAllocationInNewTLAB {
  startTime = 13:07:51.777
  objectClass = byte[] (classLoader = bootstrap)
  allocationSize = 100.0 kB
  tlabSize = 512.0 kB
  eventThread = "main" (javaThreadId = 1)
  stackTrace = [
    com.github.hashjang.jfr.test.TestAllocOutsideTLAB.main(String[]) line: 102
  ]
}

jdk.ObjectAllocationOutsideTLAB {
  startTime = 13:07:51.784
  objectClass = byte[] (classLoader = bootstrap)
  allocationSize = 100.0 kB
  eventThread = "main" (javaThreadId = 1)
  stackTrace = [
    com.github.hashjang.jfr.test.TestAllocOutsideTLAB.main(String[]) line: 102
  ]
}
//省略其他事件的详细信息，这里每种挑一个展示


countOf1KBObjectAllocationInNewTLAB: 2
countOf100KBObjectAllocationInNewTLAB: 2
countOf1KBObjectAllocationOutsideTLAB: 0
countOf100KBObjectAllocationOutsideTLAB: 190