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本文主要研究下JvmGcMetrics的managementExtensionsPresent

JvmGcMetrics

micrometer-core-1.0.3-sources.jar!/io/micrometer/core/instrument/binder/jvm/JvmGcMetrics.java

@NonNullApi
@NonNullFields
public class JvmGcMetrics implements MeterBinder {private static final Logger logger = LoggerFactory.getLogger(JvmGcMetrics.class);private boolean managementExtensionsPresent = isManagementExtensionsPresent();@Overridepublic void bindTo(MeterRegistry registry) {AtomicLong maxDataSize = new AtomicLong(0L);Gauge.builder("jvm.gc.max.data.size", maxDataSize, AtomicLong::get).tags(tags).description("Max size of old generation memory pool").baseUnit("bytes").register(registry);AtomicLong liveDataSize = new AtomicLong(0L);Gauge.builder("jvm.gc.live.data.size", liveDataSize, AtomicLong::get).tags(tags).description("Size of old generation memory pool after a full GC").baseUnit("bytes").register(registry);Counter promotedBytes = Counter.builder("jvm.gc.memory.promoted").tags(tags).baseUnit("bytes").description("Count of positive increases in the size of the old generation memory pool before GC to after GC").register(registry);Counter allocatedBytes = Counter.builder("jvm.gc.memory.allocated").tags(tags).baseUnit("bytes").description("Incremented for an increase in the size of the young generation memory pool after one GC to before the next").register(registry);if (this.managementExtensionsPresent) {// start watching for GC notificationsfinal AtomicLong youngGenSizeAfter = new AtomicLong(0L);for (GarbageCollectorMXBean mbean : ManagementFactory.getGarbageCollectorMXBeans()) {if (mbean instanceof NotificationEmitter) {((NotificationEmitter) mbean).addNotificationListener((notification, ref) -> {final String type = notification.getType();if (type.equals(GarbageCollectionNotificationInfo.GARBAGE_COLLECTION_NOTIFICATION)) {CompositeData cd = (CompositeData) notification.getUserData();GarbageCollectionNotificationInfo notificationInfo = GarbageCollectionNotificationInfo.from(cd);if (isConcurrentPhase(notificationInfo.getGcCause())) {Timer.builder("jvm.gc.concurrent.phase.time").tags(tags).tags("action", notificationInfo.getGcAction(), "cause", notificationInfo.getGcCause()).description("Time spent in concurrent phase").register(registry).record(notificationInfo.getGcInfo().getDuration(), TimeUnit.MILLISECONDS);} else {Timer.builder("jvm.gc.pause").tags(tags).tags("action", notificationInfo.getGcAction(),"cause", notificationInfo.getGcCause()).description("Time spent in GC pause").register(registry).record(notificationInfo.getGcInfo().getDuration(), TimeUnit.MILLISECONDS);}GcInfo gcInfo = notificationInfo.getGcInfo();// Update promotion and allocation countersfinal Map<String, MemoryUsage> before = gcInfo.getMemoryUsageBeforeGc();final Map<String, MemoryUsage> after = gcInfo.getMemoryUsageAfterGc();if (oldGenPoolName != null) {final long oldBefore = before.get(oldGenPoolName).getUsed();final long oldAfter = after.get(oldGenPoolName).getUsed();final long delta = oldAfter - oldBefore;if (delta > 0L) {promotedBytes.increment(delta);}// Some GC implementations such as G1 can reduce the old gen size as part of a minor GC. To track the// live data size we record the value if we see a reduction in the old gen heap size or// after a major GC.if (oldAfter < oldBefore || GcGenerationAge.fromName(notificationInfo.getGcName()) == GcGenerationAge.OLD) {liveDataSize.set(oldAfter);final long oldMaxAfter = after.get(oldGenPoolName).getMax();maxDataSize.set(oldMaxAfter);}}if (youngGenPoolName != null) {final long youngBefore = before.get(youngGenPoolName).getUsed();final long youngAfter = after.get(youngGenPoolName).getUsed();final long delta = youngBefore - youngGenSizeAfter.get();youngGenSizeAfter.set(youngAfter);if (delta > 0L) {allocatedBytes.increment(delta);}}}}, null, null);}}}}//......
}
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可以看到这里会先判断managementExtensionsPresent，如果有才会注册jvm.gc.concurrent.phase.time以及jvm.gc.pause的timer指标

isManagementExtensionsPresent

    private static boolean isManagementExtensionsPresent() {try {Class.forName("com.sun.management.GarbageCollectionNotificationInfo", false,JvmGcMetrics.class.getClassLoader());return true;} catch (Throwable e) {// We are operating in a JVM without access to this level of detaillogger.warn("GC notifications will not be available because " +"com.sun.management.GarbageCollectionNotificationInfo is not present");return false;}}
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这里的话是采用类加载来判断的，如果能找到com.sun.management.GarbageCollectionNotificationInfo则为true

• 加载失败

/ # jshell
Apr 12, 2018 4:39:07 PM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
|  Welcome to JShell -- Version 10
|  For an introduction type: /help introjshell> Class.forName("com.sun.management.GarbageCollectionNotificationInfo", false, Object.class.getClassLoader())
|  java.lang.ClassNotFoundException thrown: com/sun/management/GarbageCollectionNotificationInfo
|        at Class.forName0 (Native Method)
|        at Class.forName (Class.java:374)
|        at (#1:1)jshell> /exit
|  Goodbye
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• 加载成功

/ # jshell
Apr 12, 2018 4:05:30 PM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
|  Welcome to JShell -- Version 10
|  For an introduction type: /help introjshell> Class.forName("com.sun.management.GarbageCollectionNotificationInfo", false, Object.class.getClassLoader())
$1 ==> class com.sun.management.GarbageCollectionNotificationInfo
jshell> /exit
|  Goodbye
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GarbageCollectionNotificationInfo

/Library/Java/JavaVirtualMachines/jdk-10.jdk/Contents/Home/lib/src.zip!/jdk.management/com/sun/management/GarbageCollectionNotificationInfo.java

package com.sun.management;import javax.management.openmbean.CompositeData;
import javax.management.openmbean.CompositeDataView;
import javax.management.openmbean.CompositeType;
import com.sun.management.internal.GarbageCollectionNotifInfoCompositeData;public class GarbageCollectionNotificationInfo implements  CompositeDataView {//......
}
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从类路径看，是在jdk.management的模块里头，所在包为com.sun.management。如果要是的metrics能有jvm.gc.concurrent.phase.time以及jvm.gc.pause的timer指标的话，则要求jdk里头有com.sun.management.GarbageCollectionNotificationInfo，默认是有的，如果你的jdk进行了jlink的话，则需要加上java.management以及jdk.management

java.management与jdk.management

management相关的jmod

➜  jmods ls | grep management
java.management.jmod
java.management.rmi.jmod
jdk.internal.vm.compiler.management.jmod
jdk.management.agent.jmod
jdk.management.jmod
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java.management

jmod describe java.management.jmod
java.management@10
exports java.lang.management
exports javax.management
exports javax.management.loading
exports javax.management.modelmbean
exports javax.management.monitor
exports javax.management.openmbean
exports javax.management.relation
exports javax.management.remote
exports javax.management.timer
requires java.base mandated
uses javax.management.remote.JMXConnectorProvider
uses javax.management.remote.JMXConnectorServerProvider
uses sun.management.spi.PlatformMBeanProvider
provides javax.security.auth.spi.LoginModule with com.sun.jmx.remote.security.fileloginmodule
qualified exports com.sun.jmx.remote.internal to java.management.rmi jdk.management.agent
qualified exports com.sun.jmx.remote.security to java.management.rmi jdk.management.agent
qualified exports com.sun.jmx.remote.util to java.management.rmi
qualified exports sun.management to jdk.jconsole jdk.management jdk.management.agent
qualified exports sun.management.counter to jdk.management.agent
qualified exports sun.management.counter.perf to jdk.management.agent
qualified exports sun.management.spi to jdk.internal.vm.compiler.management jdk.management
contains com.sun.jmx.defaults
contains com.sun.jmx.interceptor
contains com.sun.jmx.mbeanserver
platform macos-amd64
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可以看到java.management模块qualified exports sun.management to jdk.jconsole jdk.management jdk.management.agent，注意这里是sun.management

这个mod提供了jmx相关类库，不加的话，依赖jxm的功能会报错，比如

java.lang.IllegalStateException: Logback configuration error detected:
ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:23 - no applicable action for [jmxConfigurator], current ElementPath  is [[configuration][jmxConfigurator]]at org.springframework.boot.logging.logback.LogbackLoggingSystem.loadConfiguration(LogbackLoggingSystem.java:166)at org.springframework.boot.logging.logback.LogbackLoggingSystem.reinitialize(LogbackLoggingSystem.java:212)at org.springframework.boot.logging.AbstractLoggingSystem.initializeWithConventions(AbstractLoggingSystem.java:75)at org.springframework.boot.logging.AbstractLoggingSystem.initialize(AbstractLoggingSystem.java:60)at org.springframework.boot.logging.logback.LogbackLoggingSystem.initialize(LogbackLoggingSystem.java:114)at org.springframework.boot.context.logging.LoggingApplicationListener.initializeSystem(LoggingApplicationListener.java:264)at org.springframework.boot.context.logging.LoggingApplicationListener.initialize(LoggingApplicationListener.java:237)at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEnvironmentPreparedEvent(LoggingApplicationListener.java:200)at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEvent(LoggingApplicationListener.java:173)at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:127)at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:74)at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:54)at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:358)at org.springframework.boot.SpringApplication.run(SpringApplication.java:317)at org.springframework.boot.builder.SpringApplicationBuilder.run(SpringApplicationBuilder.java:137)
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jdk.management

jmod describe jdk.management.jmod
jdk.management@10
exports com.sun.management
requires java.base mandated
requires java.management transitive
provides sun.management.spi.PlatformMBeanProvider with com.sun.management.internal.platformmbeanproviderimpl
contains com.sun.management.internal
platform macos-amd64
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可以看到jdk.management导出了com.sun.management，注意这里是com.sun.management

小结

要想在metrics里头有jvm.gc.concurrent.phase.time以及jvm.gc.pause的timer指标，则需要添加jdk.management模块，GarbageCollectionNotificationInfo是在com.sun.management包里头，而不是sun.management包。JvmGcMetrics用到了jmx，因此也需要加上java.lang.management模块。

doc

• 聊聊springboot1.x及2.x的JvmGcMetrics的区别