摘要：序本文主要研究一下的使用。執行順序的話，先再，最后。內置了相關，可以用來解析文件，也可以在應用程序自定義事件發布出來可以采用命令啟動，也可以使用的開頭的命令在運行時操作，非常方便

本文主要研究一下Java Flight Recorder的使用。

主要有5個命令，configure、check、start、dump、stop。執行順序的話，先start再dump，最后stop。

命令實例

jcmd 5793 JFR.configure
5793:
Current configuration:

Repository path: /private/var/folders/9r/v55wkcr91m5_g8h7lhgjzgr00000gn/T/2018_09_27_16_30_53_5793

Stack depth: 64
Global buffer count: 20
Global buffer size: 512.0 kB
Thread buffer size: 8.0 kB
Memory size: 10.0 MB
Max chunk size: 12.0 MB
Sample threads: true

命令實例

jcmd 5793 JFR.start name=demojfr dumponexit=true
5793:
Started recording 1. No limit specified, using maxsize=250MB as default.

Use jcmd 5793 JFR.dump name=demojfr filename=FILEPATH to copy recording data to file.

命令實例

jcmd 5793 JFR.check
5793:
Recording 1: name=demojfr maxsize=250.0MB (running)

命令實例

jcmd 5793 JFR.dump name=demojfr filename=/tmp/demo.jfr
5793:
Dumped recording "demojfr", 480.8 kB written to:

/tmp/demo.jfr

命令實例

jcmd 5793 JFR.stop name=demojfr
5793:
Stopped recording "demojfr".

JMC打開jfr文件實例截圖如下：

    @Test
    public void testReadJfr() throws IOException {
        Path p = Paths.get(getClass().getClassLoader().getResource("demo.jfr").getPath());
        List events = RecordingFile.readAllEvents(p);
        events.stream()
                .forEach(e -> LOGGER.info("eventType:{},startTime:{},endTime:{},fields:{}",e.getEventType().getName(),e.getStartTime(),e.getEndTime(),e.getFields()));
        List eventNames = events.stream()
                .map(e -> e.getEventType().getName())
                .distinct()
                .collect(Collectors.toList());
        System.out.println(eventNames.toString());
    }

直接使用jdk的api即可以解析jfr文件，讀出RecordedEvent

eventType類型輸出如下：

[jdk.ExceptionStatistics, jdk.NativeMethodSample, jdk.ThreadSleep, jdk.JavaMonitorWait, jdk.CPULoad, jdk.JavaThreadStatistics, jdk.ClassLoadingStatistics, jdk.CompilerStatistics, jdk.ClassLoaderStatistics, jdk.ModuleExport, jdk.CodeCacheStatistics, jdk.CodeSweeperStatistics, jdk.GCConfiguration, jdk.ActiveSetting, jdk.ActiveRecording, jdk.InitialSystemProperty, jdk.InitialEnvironmentVariable, jdk.CPUInformation, jdk.CPUTimeStampCounter, jdk.ThreadAllocationStatistics, jdk.PhysicalMemory, jdk.NativeLibrary, jdk.CompilerConfiguration, jdk.CodeCacheConfiguration, jdk.CodeSweeperConfiguration, jdk.IntFlag, jdk.UnsignedIntFlag, jdk.LongFlag, jdk.UnsignedLongFlag, jdk.DoubleFlag, jdk.BooleanFlag, jdk.StringFlag, jdk.ThreadEnd, jdk.ThreadCPULoad, jdk.NetworkUtilization, jdk.ThreadStart, jdk.ThreadContextSwitchRate, jdk.GCSurvivorConfiguration, jdk.GCTLABConfiguration, jdk.GCHeapConfiguration, jdk.YoungGenerationConfiguration, jdk.SystemProcess, jdk.ThreadDump, jdk.JVMInformation, jdk.OSInformation, jdk.ModuleRequire]

除了系統定義的eventType，還可以自定義event

DemoEvent

@Label("Demo Event")
@Description("Helps the programmer getting started")
public class DemoEvent extends Event {
    @Label("Message")
    private String message;

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

發布事件

        DemoEvent event = new DemoEvent();
        event.setMessage("hello, world!");
        event.commit();

之后使用api解析jfr文件，可以看到自定義的event，其name為com.example.jfr.DemoEvent
可以使用如下參數啟動-XX:StartFlightRecording=duration=120s,filename=/tmp/event.jfr,settings=default,name=DemoEventRecording

JDK11關于jfr的模塊有兩個，分別是jdk.jfr.jmod以及jdk.management.jfr.jmod，其具體內容如下：

?  jmods ../bin/jmod describe jdk.jfr.jmod
jdk.jfr@11
exports jdk.jfr
exports jdk.jfr.consumer
requires java.base mandated
qualified exports jdk.jfr.internal.management to jdk.management.jfr
contains jdk.jfr.events
contains jdk.jfr.internal
contains jdk.jfr.internal.cmd
contains jdk.jfr.internal.consumer
contains jdk.jfr.internal.dcmd
contains jdk.jfr.internal.handlers
contains jdk.jfr.internal.instrument
contains jdk.jfr.internal.jfc
contains jdk.jfr.internal.settings
contains jdk.jfr.internal.test
contains jdk.jfr.internal.types
platform macos-amd64

?  jmods ../bin/jmod describe jdk.management.jfr.jmod
jdk.management.jfr@11
exports jdk.management.jfr
requires java.base mandated
requires java.management transitive
requires jdk.jfr
requires jdk.management
provides sun.management.spi.PlatformMBeanProvider with jdk.management.jfr.internal.FlightRecorderMXBeanProvider
contains jdk.management.jfr.internal
platform macos-amd64

Java Flight Recorder是一款優秀的java應用診斷工具，以前是商業版的特性，現在在java11當中開源出來，它導出的jfr文件可以用Java Mission Control來分析。

JDK11內置了相關API，可以用來解析jfr文件，也可以在應用程序自定義事件發布出來

JFR可以采用JVM命令啟動，也可以使用jcmd的JFR.開頭的命令在運行時操作，非常方便

Using Java Flight Recorder

Java Flight Recorder Cheat Sheet

2 Diagnostic Command Reference

Clarifying some confusion around Java Flight Recordings

Java Flight Recorder：The Secret Arrow in Your Quiver