英文文献 科技类 原文及翻译 电子 电气 自动化 通信74Word文件下载.docx

英文文献 科技类 原文及翻译 电子 电气 自动化 通信74Word文件下载.docx

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you,thesoftwaredeveloper,tocreatesoftwareagentsthatcanmonitorandcontrolyourJava

programminglanguageapplications.JVMTIisnewintheJava2SoftwareDevelopmentKit

（SDK）,StandardEdition,version1.5.0.ItreplacestheJavaVirtualMachineProfilingInterface

（JVMPI）,whichhadbeenincludedasanexperimentalfeatureoftheJava2SDKsinceversion

1.1.JVMTIisdescribedinJSR-163.

ThisarticleillustrateshowtouseJVMTItocreateadebuggingandprofilingtoolforJavaapplications.Suchatool,alsocalledanagent,usesthefunctionalityexposedbytheinterface

toregisterfornotificationofeventsastheyoccurintheapplication,andtoqueryandcontrol

theapplication.JVMTIdocumentationisavailablehere.AJVMTIagentcanbeusefulfordebuggingandtuninganapplication.Itcanillustrateaspectsoftheapplication,suchas

memoryallocation,CPUutilization,andlockcontention.

EventhoughJVMPIisexperimental,itisbeingusedbymanyJavatechnologydevelopers,andin

severalcommercially-availableJavaapplicationprofilers.PleasenotethatdevelopersarestronglyencouragedtouseJVMTIinsteadofJVMPI.JVMPIwillbediscontinuedintheverynearfuture.

JVMTIimprovesuponthefunctionalityandperformanceofJVMPIinmanyways.Forexample:

JVMTIreliesonacallbackforeachevent.ThisismoreefficientthantheJVMPIdesignofusing

eventstructures,whichneededtobemarshalledandunmarshalled.

JVMTIcontainsfourtimesasmanyfunctionsasJVMPI（includingmanymorefunctionsto

obtaininformationaboutvariables,fields,methods,andclasses）.ForacompleteindexoftheJVMTI

functions,seetheFunctionIndexpage.

JVMTIprovidesnotificationformoretypesofeventsthandoesJVMPI,includingexception

events,fieldaccessandmodificationevents,andbreakpointandsingle-stepevents.

SomeoftheJVMPIeventsthatwereneverfullyutilized,suchasarenanewanddelete,orthat

canbebetterobtainedthroughbytecodeinstrumentation,ortheJVMTIfunctionsthemselves,（such

asheapdumpandobjectallocation）havebeendropped.Adescriptionoftheeventsisavailableat

theEventIndexpage.

JVMTIiscapability-based,whereasJVMPIwas"

allornothing"

withcorrespondingperformanceimpact.

JVMPIheapfunctionalitydidnotscale.

JVMPIhadnoerrorreturninformation.

JVMPIwasdeeplyinvasiveonVMimplementationswithresultingmaintenanceissuesand

performanceimpacts.

JVMPIisexperimentalandwillbediscontinuedverysoon.

Intheremainderofthisarticle,wepresentasimpleagentthatusesJVMTIfunctionstoextract

informationfromaJavaapplication.Theagentmustbewritteninnativecode.Thesample

agentshownhereiswrittenintheCprogramminglanguage.Youcandownloadthecompletesampleagentcodehere.Thefollowingparagraphsdescribehowanagentisinitialized,and

howtheagentusesJVMTIfunctionstoextractinformationaboutaJavaapplication,aswellas

howtocompileandruntheagent.Thesamplecodeandcompilationstepsarespecificto

UNIXenvironments,butcanbemodifiedforusewithWindows.TheagentdescribedherecanbeusedtoanalyzethethreadsandtodetermineJVMmemoryusageinanyJavaapplication.

AsimpleprogramwrittenintheJavaprogramminglanguage,calledSimpleThread.java,isincludedandcanbedownloadedhere.WeuseThreadSample.javatodemonstratetheexpectedoutputfromtheagent.

ThefunctionalityofJVMTIismuchmoreextensivethanwecandetailhere,butthecode

inthisarticleshouldprovideastartingplacefordevelopingprofilingtoolstomeetyourown

specificneeds.

AgentInitialization

Thissectiondescribesthecodethatisusedtoinitializetheagent.Tobeginwith,theagentmustincludethejvmti.hfilewiththestatement:

#include<

jvmti.h>

.

Inaddition,theagentmustcontainafunctioncalledAgent_OnLoad,whichisinvokedwhenthelibraryisloaded.TheAgent_OnLoadfunctionisusedtosetupfunctionalitythatis

1requiredpriortoinitializingtheJavavirtualmachine（JVM）.TheAgent_OnLoadsignaturelookslikethis:

JNIEXPORTjintJNICALLAgent_OnLoad（JavaVM*jvm,char*options,void

*reserved）{

...

/*WereturnJNI_OKtosignifysuccess*/

returnJNI_OK;

}

Inoursamplecode,wemustenableseveralcapabilitiesfortheJVMTIfunctionsand

eventsthatwewillbeusing.Itisgenerallydesired,andinsomecasesrequired,toaddthesecapabilitiesintheAgent_OnLoadfunction.Thecapabilitiesnecessaryforeachfunctionor

eventaredescribedintheJavaVirtualMachineToolInterfacepages.Forexample,tousetheInterruptT