dtrace topics java

7/24/2019 Dtrace Topics Java

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# ./jflow.d

Greeting.greet

-> java/io/PrintStream.println

-> java/io/PrintStream.print

-> java/io/PrintStream.write

-> java/io/PrintStream.ensureOpen java/io/riter.write

-> java/io/!ufferedriter.write

-> java/io/!ufferedriter.ensureO

java/io/!ufferedriter.min

java/lang/String.get"hars

-> java/lang/Sstem.arra$op


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DTrace Topics: Java

This presentation is about DTrace and Java, and ispart of the DTrace Topics coection!

These sides cover"

> DTrace #ecap> Java and DTrace

> The hotspot $rovider

> hotspot %&ampes

> #esources


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'

DTrace Recap

( )enera understandin) of DTrace is assumed*no+ed)e for this presentation!

f you are ne+ to DTrace, try startin) +ith the

presentation caed DTrace Topics" ntro! The ne&t t+o sides are a short summary of DTrace,

if needed!


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-

What is DTrace

DTrace is a dynamic troubeshootin) and anaysistoo first introduced in the Soaris 10 and.penSoaris operatin) systems!

DTrace is many thin)s, in particuar"> ( tool, /usr/sbin/dtrace

> ( programming languageinterpreter, the D an)ua)e

> (n instrumentationframe+or*

DTrace operates +ith o+ overhead +hen in use,and ero overhead +hen not!

DTrace is desi)ned to be safe for production use!


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What is DTrace

DTrace can observe the entire soft+are stac* fromone too! t is i*e a combination of,> truss, sotruss, apptrace, mdb, oc*stat, pre&/tnf, 3, a+*

root and users +ith DTrace privie)es can use it! DTrace traces events at dynamic instrumentation

points caed probes! There are thousands of them!

providersare ibraries of reated probes! 4hen probes fire, arbitry actionscan be performed,

> %)" print functions and ar)uments, measure atencies,process data, +a* process and *erne memory, !!!


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5

Java and DTrace

n the first reease of Soaris 10, DTrace provided ajstack()action to read Java stac* traces!

6or JD 1!-!2 and !0, prototype DTrace Java

providers +ere reeased as oadabe 8M a)entibraries, first named djvm then dvm!

The hotspotDTrace Java provider +as inte)ratedin JD 5!0, ready for immediate use!


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jstack()

This can be used +ith"> The profie provider, to sampe fre9uent stac* traces!

This can identify Java code hot spots!

>

The pid provider, to sho+ ho+ Java interacts +ith useribraries!

> The sysca provider, to determine +hat Java causes thesystem to do!


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jstack() example

The foo+in) sho+s whyJava caused a read;


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djvm/dvm Provider

f possibe, move the appication to JD 5!0 and usethe inte)rated hotspot provider!

f you are stuc* on JD 1!-!2 or !0, you can try the

d>vm/dvm prototype provider! They re9uire command ine confi)uration and the

appication to be restarted!

The provider can be do+noaded from,> https"//soaris10?dtrace?vm?a)ents!dev!>ava!net

Some e&ampes of its usa)e are here,> http"//bo)s!sun!com/ah/entry/dtracin)@>ava
https://solaris10-dtrace-vm-agents.dev.java.net/http://blogs.sun.com/ahl/entry/dtracing_javahttp://blogs.sun.com/ahl/entry/dtracing_javahttps://solaris10-dtrace-vm-agents.dev.java.net/


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hotspot Provider Probes

hotspot provides numerous probes, incudin)"> 3ass events,class-loaded ( cass oadedclass-unloaded ( cass unoaded

> Method invocation,method-entry ( method be)insmethod-return ( method competed

> .b>ect events,object-alloc (n ob>ect +as aocated

> Aarba)e coect,gc-begin System +ide A3 be)insgc-end System +ide A3 ended


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hotspot Provider Probes

> Thread events,thread-start ( thread has startedthread-stop ( thread competed

> Monitor events

> 8M events

The method-*probes can de)rade performance,and are ony enabed +ith the 8M fa)

ExtendedDTraceProbes!

The fu reference for probes and their ar)uments is"http"//>ava!sun!com/>avase/5/docs/technotes/)uides/vm/dtrace!htm
http://java.sun.com/javase/6/docs/technotes/guides/vm/dtrace.htmlhttp://java.sun.com/javase/6/docs/technotes/guides/vm/dtrace.html


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hotspot Example !

The hotspot provider +i be demonstrated bytracin) a simpe Java pro)ram!

The foo+in) Areetin)!>ava code may oo* famiiar,

many Java tutorias be)in +ith somethin) simiar"

J $at Greeting.java

pu9li$ $lass Greeting +

pu9li$ void greet + Sstem.out.println*Kello Tra$eL*

0

0

Greeting class


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hotspot Example !

Bo+ the test harness"

J $at TestGreeting.java

pu9li$ $lass TestGreeting +

pu9li$ stati$ void mainString12 args +

Greeting hello ) new Greeting

while true +

hello.greet

tr +

Thread.$urrentThread.sleep:333

0 $at$h Bnterrupted%($eption e + 0

0

0

0

TestGreeting class

call greet method

everysecond


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hotspot Example !

3ompiin), e&ecutin)"

This simpe pro)ram produces some *no+n eventsthat +e can trace!

J java$ TestGreeting.java

J java TestGreeting

Kello Tra$eL

Kello Tra$eLKello Tra$eL

Kello Tra$eL

M"

slowly scrolling output


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Example !: jstack()

4e +i start +ith >stac*;< ;not hotspotC

# dtra$e -n &ss$all''write'entr /e(e$name )) *java*/ + jsta$, 0&

3 45675 write'entr

li9$.so.:;write=3(4 li9jvm.so;:$hpiCwriteDCip,vBB=3(a3

li9jvm.so;EFNrite=3(8D

li9java.so;write!tes=3(:57

li9java.so;EavajavaioCileOutputStreamwrite!tes=3(8f

java/io/CileOutputStream.write!tes1!BBF

java/io/CileOutputStream.write1!BBF java/io/!ufferedOutputStream.flush!ufferF

java/io/!ufferedOutputStream.flushF

java/io/PrintStream.write1!BBF

sun/nio/$s/Stream%n$oder.write!tesF

sun/nio/$s/Stream%n$oder.implClush!ufferF

1...$ontinued...2


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Example !: jstack()

> #ead the stac* trace above Areetin)!)reet carefuy!

o+ many Java casses do you reco)nieE

sun/nio/$s/Stream%n$oder.flush!ufferF

java/io/OutputStreamriter.flush!ufferF

java/io/PrintStream.newHineF

java/io/PrintStream.printlnHjava/lang/StringF

Greeting.greetF

TestGreeting.main1Hjava/lang/StringF

Stu9?out

li9jvm.so;:$EEava"allsH$allhelperDCpnEEavaFaluepnNmethodKan

li9jvm.so;:$"osose($eptionwrapperDCpCpnEEavaFaluepnNmetho

li9jvm.so;:$EEava"alls%$allDCpnEEavaFaluenNmethodKandlepn?E

li9jvm.so;:$?jniinvo,estati$DCpnKEB%nvpnEEavaFaluepnBj

li9jvm.so;jni"allStati$FoidNethod=3(:5d

java;EavaNain=3(d83 li9$.so.:;thrsetup=3(5@

li9$.so.:;lwpstart

Ah-ha


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Example !: "istin# Probes

Bo+ to see +hat the hotspotprovider can do"

> 101- probes, -=: uni9ue probe names FF deep visibiityC

# dtra$e -ln &hotspotQ'''&

B P?OFB%? NOH% C"TBO IN%

5@:38 hotspotjni@4A88A li9jvm.so jniGetO9je$t?efTpe GetO9

5@:37 hotspotjni@4A88A li9jvm.so jniGetO9je$t?efTpe GetO95@:35 hotspotjni@4A88A li9jvm.so jniGetPrimitiveIrra"riti$al GetPr

5@:3D hotspotjni@4A88A li9jvm.so jniGetPrimitiveIrra"riti$al GetPr

5@:34 hotspotjni@4A88A li9jvm.so jniGetShortIrra%lements GetSh

1...2

# dtra$e -ln &hotspotQ'''& R w$ -l

:3:5# dtra$e -ln &hotspotQ'''& R aw, &+print J50& R sort -u R w$ -l

766


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Example !: Tracin# Probes

4atchin) a enabed hotspot events"

.utput scros rather fast!!!

# dtra$e -n &hotspotQ'''&

dtra$e' des$ription &hotspotQ'''& mat$hed :3:7 pro9es

"P B C"TBO'IN%

3 DD7D5 jniGetIrraHength'GetIrraHength-entr

3 DD7DD jniGetIrraHength'GetIrraHength-return

3 DD5@6 jniGetO9je$tCield'GetO9je$tCield-entr

3 DD583 jniGetO9je$tCield'GetO9je$tCield-return

3 DD5@6 jniGetO9je$tCield'GetO9je$tCield-entr

3 DD583 jniGetO9je$tCield'GetO9je$tCield-return

3 DD745 jniGet!teIrra?egion'Get!teIrra?egion-entr

3 DD74D jniGet!teIrra?egion'Get!teIrra?egion-return

3 DD75D jni%($eptionO$$urred'%($eptionO$$urred-entr

3 DD754 jni%($eptionO$$urred'%($eptionO$$urred-return

1...2


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Example !: $##re#atin# Probes

> nterestin), but some e&pected probes are missin) ;e),method?entry

# dtra$e -n &hotspotQ''' + 1pro9ename2 ) $ount 0&

dtra$e' des$ription &hotspotQ''' & mat$hed :3:7 pro9es

M"

%($eptionO$$urred-entr A

%($eptionO$$urred-return A

GetIrraHength-entr A

GetIrraHength-return A

Get!teIrra?egion-entr A

Get!teIrra?egion-return A

GetO9je$tCield-entr :D

GetO9je$tCield-return :D


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Example !: Extended Probes

%&tended probes are not activated by defaut asthey may de)rade performance on busy apps!

They can be enabed usin),

> (n option to >ava" ?GG"H%&tendedDTrace$robes> (n option to >info" ?fa) H%&tendedDTrace$robes

# java -'=%(tendedTra$ePro9es TestGreeting

Kello Tra$eL

Kello Tra$eL

Kello Tra$eL

1...2


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Example !: Extended Probes

> Bo+ +e see method?entry and method?return, +hichoccurred -=5 times +hie this +as tracin) ;- seconds

# dtra$e -n &hotspotQ''' + 1pro9ename2 ) $ount 0&dtra$e' des$ription &hotspotQ''' & mat$hed :3:7 pro9es

M"

%($eptionO$$urred-entr A

%($eptionO$$urred-return A

GetIrraHength-entr A GetIrraHength-return A

Get!teIrra?egion-entr A

Get!teIrra?egion-return A

o9je$t-allo$ A

GetO9je$tCield-entr :D

GetO9je$tCield-return :D

method-entr 76D

method-return 76D


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Example !: Tracin# %ethods

The cass and method name can be fetched fromthe probe ar)uments"

# dtra$e -n &hotspotQ'''method-entr + printf*-> U7s.UsVn*W

stringof$opinarg:W arg@W stringof$opinarg8W arg7 0&

-> Greeting.greet-> java/io/PrintStream.println



-> java/io/PrintStream.ensureOpen

-> java/io/riter.write

-> java/io/!ufferedriter.write-> java/io/!ufferedriter.ensureOpen

-> java/io/!ufferedriter.min

-> java/lang/String.get"hars

-> java/lang/Sstem.arra$op

-> java/io/!ufferedriter.flush!uffer

1...2

!ive class"method calls


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Example !: $##re#atin# %ethods

> dentify most fre9uenty caed methods!

# dtra$e -n &hotspotQ'''method-entr + $alls1stringof$opinarg:W arg@W

stringof$opinarg8Warg72 ) $ount 0

% + printa*U7As.U-@7s U7dVn*W $alls 0&

M"

Greeting.greet @

java/io/!ufferedriter.ensureOpen @

java/io/!ufferedriter.minureOpen @ java/io/!ufferedriter.writeeOpen @

java/io/!ufferedriteropflush!uffer.ensureOpenr @

java/io/!ufferedriteropinureOpen.flush!uffer @

java/io/OutputStreamritersureOpenr.write @

java/io/PrintStream.ensureOpen @

1...trun$ated...2java/nio/"har!ufferJ%n$oarraOffsetodeIrraHoop.arraOffsetodeIrraHoop @3

java/nio/!te!ufferJ%n$oarraOffsetodeIrraHoop.arraOffsetodeIrraHoop 83


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4ait a sec,

These donIt oo* ri)ht the strin)s have been corrupted!

f you see such output, the end of the copyin strin)needs to be manuay terminated!

1...2

java/nio/"har!ufferJ%n$oarraOffsetodeIrraHoop.arraOffsetodeIrraHoop @3

java/nio/!te!ufferJ%n$oarraOffsetodeIrraHoop.arraOffsetodeIrraHoop 83


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Bo+ a script is +ritten to a))re)ate methods +ithstrin) termination"

# ./jagg.d

Tra$ing... Kit "trl-" to end.

M"

Greeting.greet 8

java/io/!ufferedriter.newHine 8

java/io/PrintStream.newHine 8

java/io/PrintStream.print 8

java/io/PrintStream.println 8

java/lang/Thread.$urrentThread 8

1...2

java/nio/$harset/"oder?esult.isnderflow :@

java/nio/!uffer.position :A

java/nio/"har!uffer.arraOffset :A

java/nio/!te!uffer.arraOffset @7


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# $at jagg.d

#L/usr/s9in/dtra$e -s

dtra$e'''!%GB

+

printf*Tra$ing... Kit "trl-" to end.Vn*

0

hotspotQ'''method-entr

+

this->$lass ) $har Q $opinarg:W arg@ = :

this->$lass1arg@2 ) &V3&

this->method ) $har Q $opinarg8W arg7 = :

this->method1arg72 ) &V3&

$alls1stringofthis->$lassW stringofthis->method2 ) $ount

0

dtra$e'''%

+

printa*U7As.U-@7s U7dVn*W $alls

0


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Example !: %ethod &lo'

4ith some more scriptin), fo+ indented methodcas can be printed"

# ./jflow.d

Greeting.greet -> java/io/PrintStream.println



-> java/io/PrintStream.ensureOpen

java/io/riter.write -> java/io/!ufferedriter.write

-> java/io/!ufferedriter.ensureOpen

java/io/!ufferedriter.min


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2:

Example !: jlo'd

# $at jflow.d

#L/usr/s9in/dtra$e -s

#pragma option uiet

hotspotQ'''method-entr

+

self->indent==

printf*UQs Us Us.UsVn*W self->indentW **W *->*W

stringof$opinarg:W arg@W stringof$opinarg8Warg7

0

hotspotQ'''method-return+

printf*UQs Us Us.UsVn*W self->indentW **W *indent--

0


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2=

Example !: *tack &lo'

DTrace can observe a ayers of the soft+are stac*!

The foo+in) e&ampe demonstrates this capabiity,and +as actuay from the prototype provider,

http"//bo)s!sun!com/ah/entry/dtracin)@>ava -> java/io/BnputStream?eader'read

-> sun/nio/$s/Streame$oder'read

-> sun/nio/$s/Streame$oder'read3

-> li9$.so.:'mallo$

-> li9$.so.:'smallo$ sun/nio/$s/Streame$oder'read

-> sun/nio/$s/Streame$oder'ensureOpen


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'0

Example !: +bject $llocation

The creation of a ne+ ob>ect can be traced +ithob>ect?aoc"

# dtra$e -n &hotspotQ'''o9je$t-allo$ + printf*new UsVn*W

stringof$opinarg:W arg@ 0&

new java/nio/Keap"har!uffer




1...2


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Example !: %ethod Times

4ith method?entry and method?return probes, andDTraceIs abiity to measure nanosecondtimestamps, the time to e&ecute methods can bemeasured!

This can hep identify bottenec*s in Java code!

Thin)s start to )et a itte harder! Ke a+are of,> overappin) methods

> mutipe Java threads e&ecutin) concurrenty

> Java threads conte&t s+itchin) off the 3$Ls

> DTrace overheads at nanosecond resoutions

>

recursive methodsE


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Example !: What,s next

6urther anaysis can be performed usin)"> .ther hotspot probes

> .ther DTrace providers

>

Scriptin) to identify events of interest The possibiities for anaysis are near?endess! This

is )reat if you are troubeshootin) a *no+n probem as DTrace shoud have the po+er to find it!


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Reso-rces

To earn more about DTrace and Java,http"//>ava!sun!com/>avase/5/docs/technotes/)uides/vm/dtrace!htm

Search the nternet for DTrace Java, in particuar

are artices +ritten by">(dam eventha> ey .Iair

6ind %&ampes of DTracin) Java in/usr/>d*/instances/>d*1!5!0/sampe/dtrace/hotspot

3hec* my bo)" http"//bo)s!sun!com/brendan
http://java.sun.com/javase/6/docs/technotes/guides/vm/dtrace.htmlhttp://java.sun.com/javase/6/docs/technotes/guides/vm/dtrace.html


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Brendan GreggbrendanNsun!com

dtrace topics java

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