Java Flight Recorder小试牛刀

摘要：序本文主要研究一下的使用。执行顺序的话，先再，最后。内置了相关，可以用来解析文件，也可以在应用程序自定义事件发布出来可以采用命令启动，也可以使用的开头的命令在运行时操作，非常方便

本文主要研究一下Java Flight Recorder的使用。

主要有5个命令，configure、check、start、dump、stop。执行顺序的话，先start再dump，最后stop。

命令实例

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

命令实例

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.

命令实例

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

命令实例

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

/tmp/demo.jfr

命令实例

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

JMC打开jfr文件实例截图如下：

    @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，读出RecordedEvent

eventType类型输出如下：

[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]

除了系统定义的eventType，还可以自定义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;
    }
}

发布事件

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

之后使用api解析jfr文件，可以看到自定义的event，其name为com.example.jfr.DemoEvent
可以使用如下参数启动-XX:StartFlightRecording=duration=120s,filename=/tmp/event.jfr,settings=default,name=DemoEventRecording

JDK11关于jfr的模块有两个，分别是jdk.jfr.jmod以及jdk.management.jfr.jmod，其具体内容如下：

➜  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是一款优秀的java应用诊断工具，以前是商业版的特性，现在在java11当中开源出来，它导出的jfr文件可以用Java Mission Control来分析。

JDK11内置了相关API，可以用来解析jfr文件，也可以在应用程序自定义事件发布出来

JFR可以采用JVM命令启动，也可以使用jcmd的JFR.开头的命令在运行时操作，非常方便

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