JVM in Action

WWW.SITE2MAX.PRO PowerPoint & KeyNote Templates +7.ιʔείʔυೖ໳ @tan_go238

Go Tanaka ओʹ1)1ॻ͍ͯ·͢ +7.ιʔείʔυϦʔσΟϯά͸झຯ 【運営スタッフ】関西Javaエンジニアの会 Scala関西 Summit Freelance Engineer
@UBO@HP

ࠂ஌ 4DBMBؔ੢4VNNJU ೔࣌೥݄೔ ౔ ৔ॴఱຬݚमηϯλʔʢ+3େࡕͷྡͷӺͷ͙ۙ͘͢ʣ

͜ͷηογϣϯͰͷ+7.͸)PU4QPU7.ͷ͜ͱΛࢦ͠·͢ɻ +BWBݴޠ࢓༷΍+BWBԾ૝Ϛγϯ࢓༷ʹ͸هࡌ͞Ε͍ͯͳ͍͜ͱ͕ଟ͍Ͱ͢ɻ ΑͬͯɺҰ෦࣮ࡍͷಈ࡞ͱҟͳΔ͜ͱ͕͋Δ͔΋͠Ε·ͤΜɻ ·ͨझຯͰ+7.Λௐ΂͍ͯΔͨΊҰ෦ޡΓ͕͋Δ͔΋͠Ε·ͤΜ͕ ͦͷͱ͖͸͝ࢦఠ͍ͩ͘͞ɻ ஫ҙ

+7.ͷιʔείʔυΛ͢΂ͯཧղ͢Δͷ͸೉͍͠Ͱ͕͢ ༻ޠΛ͓͑ͯ͞ͻͱͭͻͱͭಈ࡞Λཧղ͍ͯ͘͠ͱ ιʔείʔυࣗମ͸៉ྷʹॻ͔Εͯ͋Γʢͳ͔ʹ͸μʔςΟϋοΫ΋͋Δʣ ·ͨιʔείʔυதͷίϝϯτ΍υΩϡϝϯτ΋ॆ࣮͍ͯ͠ΔͷͰ ҙ֎ͱ؆୯ʹಡΊΔΑ͏ʹͳΕ·͢ʢଟগͷؾ߹͍ͱࠜੑ͕ඞཁʣ ͜ͷηογϣϯͰ͸Ұ൪࠷ॳͷͱ͔͔ͬΓ෦෼ʹ͍ͭͯ࿩ͤͨΒͱࢥͬͯͨͷͰ͕͢ ్தɺΨοπϦ͍ͬͯ͠·ͬͨͷͰԿͱͳ͘ฉ͖ྲྀͯ͠΋Β͑Ε͹ͱࢥ͍·͢ ͸͡Ίʹ

࣭໰ 0QFO+%,ͷίϛολͷਓ͍·͔͢ʁ +7.ͷτϥϒϧγϡʔςΟϯά͕࢓ࣄͷਓ͍·͔͢ʁ

0QFO+%,ͷίϛολͷਓ͍·͔͢ʁ +7.ͷτϥϒϧγϡʔςΟϯά͕࢓ࣄͷਓ͍·͔͢ʁ :FTɿ஌ͬͯΔ಺༰ͳͷͰɺಛʹ͜ͷηογϣϯฉ͘ඞཁͳ͍Ͱ͢ /Pɿ஌ͬͯͯ΋࢖Θͳ͍ͷͰɺಛʹ͜ͷηογϣϯฉ͘ඞཁͳ͍Ͱ͢ ࣭໰

໨࣍

༻ޠΛ͓͑͞Α͏ 001·ΘΓ ϝϞϦϨΠΞ΢τ +7.ͷىಈ ໨࣍

༻ޠΛ͓͑͞Α͏ )PU4QPU(MPTTBSZPG5FSNT )PU4QPUͰΑ͘࢖ΘΕΔ༻ޠʹ͍ͭͯղઆ͞Ε͍ͯΔ BEBQUJWFTQJOOJOHCJBTFEMPDLJOHCMPDLTUBSUUBCMFCPPUTUSBQDMBTTMPBEFSCZUFDPEFWFSJpDBUJPO $$PNQJMFS$$PNQJMFSDBSEUBCMFDMBTTEBUBTIBSJOHDMBTTIJFSBDIZBOBMZTJTDPEFDBDIF DPNQBDUJPODPODVSSFODZDPODVSSFOUHBSCBHFDPMMFDUJPODPQZJOHHBSCBHFDPMMFDUJPOEFPQUJNJ[BUJPO EFQFOEFODZFEFOGSFFMJTUHBSCBHFDPMMFDUJPOHBSCBHFDPMMFDUJPOSPPU($NBQHFOFSBUJPOBMHBSCBHF DPMMFDUJPOIBOEMFIPUMPDLJOUFSQSFUFS+*5DPNQJMFST+/*+7.5*LMBTTQPJOUFSNBSLXPSEONFUIPE PCKFDUIFBEFSPCKFDUQSPNPUJPOPMEHFOFSBUJPOPOTUBDLSFQMBDFNFOUPPQQBSBMMFMDMBTTMPBEJOHQBSBMMFM HBSCBHFDPMMFDUJPOQFSNBOFOUHFOFSBUJPOSFNFNCFSFETFUTBGFQPJOUTFBPGOPEFT
4FSWJDFBCJMJUZ"HFOU 4" TUBDLNBQ4UBDL.BQ5BCMFTVSWJWPSTQBDFTZODISPOJ[BUJPO5-"# VODPNNPOUSBQWFSJpFS7.0QFSBUJPOTXSJUFCBSSJFSZPVOHHFOFSBUJPO http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html

༻ޠΛ͓͑͞Α͏ ͜ΕΒͷ༻ޠ͸͢΂֮ͯ͑Δඞཁ͸ͳ͍ ग़͖ͯͨͱ͖ʹௐ΂Ε͹͍͍ ίʔυதʹ΋આ໌͕ॻ͍ͯ͋Δ৔߹͕ଟ͍

༻ޠΛ͓͑͞Α͏ )PU4QPU(MPTTBSZPG5FSNT )PU4QPUͰΑ͘࢖ΘΕΔ༻ޠʹ͍ͭͯղઆ͞Ε͍ͯΔ BEBQUJWFTQJOOJOHCJBTFEMPDLJOHCMPDLTUBSUUBCMFCPPUTUSBQDMBTTMPBEFSCZUFDPEFWFSJpDBUJPO $$PNQJMFS$$PNQJMFSDBSEUBCMFDMBTTEBUBTIBSJOHDMBTTIJFSBDIZBOBMZTJTDPEFDBDIF DPNQBDUJPODPODVSSFODZDPODVSSFOUHBSCBHFDPMMFDUJPODPQZJOHHBSCBHFDPMMFDUJPOEFPQUJNJ[BUJPO EFQFOEFODZFEFOGSFFMJTUHBSCBHFDPMMFDUJPOHBSCBHFDPMMFDUJPOSPPU($NBQHFOFSBUJPOBMHBSCBHF DPMMFDUJPOIBOEMFIPUMPDLJOUFSQSFUFS+*5DPNQJMFST+/*+7.5*LMBTTQPJOUFSNBSLXPSEONFUIPE PCKFDUIFBEFSPCKFDUQSPNPUJPOPMEHFOFSBUJPOPOTUBDLSFQMBDFNFOUPPQQBSBMMFMDMBTTMPBEJOHQBSBMMFM HBSCBHFDPMMFDUJPOQFSNBOFOUHFOFSBUJPOSFNFNCFSFETFUTBGFQPJOUTFBPGOPEFT
4FSWJDFBCJMJUZ"HFOU 4" TUBDLNBQ4UBDL.BQ5BCMFTVSWJWPSTQBDFTZODISPOJ[BUJPO5-"# VODPNNPOUSBQWFSJpFS7.0QFSBUJPOTXSJUFCBSSJFSZPVOHHFOFSBUJPO http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html

༻ޠΛ͓͑͞Α͏ )PU4QPU(MPTTBSZPG5FSNT BEBQUJWFTQJOOJOHCJBTFEMPDLJOHCMPDLTUBSUUBCMFCPPUTUSBQDMBTTMPBEFSCZUFDPEFWFSJpDBUJPO $$PNQJMFS$$PNQJMFSDBSEUBCMFDMBTTEBUBTIBSJOHDMBTTIJFSBDIZBOBMZTJTDPEFDBDIF DPNQBDUJPODPODVSSFODZDPODVSSFOUHBSCBHFDPMMFDUJPODPQZJOHHBSCBHFDPMMFDUJPOEFPQUJNJ[BUJPO EFQFOEFODZFEFOGSFFMJTUHBSCBHFDPMMFDUJPOHBSCBHFDPMMFDUJPOSPPU($NBQHFOFSBUJPOBMHBSCBHF DPMMFDUJPOIBOEMFIPUMPDLJOUFSQSFUFS+*5DPNQJMFST+/*+7.5*LMBTTQPJOUFSNBSLXPSEONFUIPE PCKFDUIFBEFSPCKFDUQSPNPUJPOPMEHFOFSBUJPOPOTUBDLSFQMBDFNFOUPPQQBSBMMFMDMBTTMPBEJOHQBSBMMFM HBSCBHFDPMMFDUJPOQFSNBOFOUHFOFSBUJPOSFNFNCFSFETFUTBGFQPJOUTFBPGOPEFT 4FSWJDFBCJMJUZ"HFOU
4" TUBDLNBQ4UBDL.BQ5BCMFTVSWJWPSTQBDFTZODISPOJ[BUJPO5-"# VODPNNPOUSBQWFSJpFS7.0QFSBUJPOTXSJUFCBSSJFSZPVOHHFOFSBUJPO http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html )PU4QPUͰΑ͘࢖ΘΕΔ༻ޠʹ͍ͭͯղઆ͞Ε͍ͯΔ

༻ޠΛ͓͑͞Α͏ 001 0SEJOBSZ0CKFDU1PJOUFS +BWBΦϒδΣΫτ͸001ͱͯ͠දݱ͞Εɺώʔϓ্ʹ͋Δ 001͸$$ ͷϙΠϯλͰώʔϓ಺ͷҐஔΛࢦ͢

༻ޠΛ͓͑͞Α͏ PCKFDUIFBEFS ($͕؅ཧ͢Δ͢΂ͯͷώʔϓΦϒδΣΫτ 001 ͷઌ಄ͷڞ௨ߏ଄ ώʔϓΦϒδΣΫτͷϨΠΞ΢τ΍λΠϓɺ($ঢ়ଶɺಉظঢ়ଶɺ ҰҙʹͳΔϋογϡίʔυʹؔ͢Δجຊతͳ৘ใؚ͕·Ε͍ͯΔ ͭͷϫʔυͰߏ੒͞Ε͍ͯΔʢ.BSL ,MBTTʣ ഑ྻͷ௚ޙʹ͸௕͞ϑΟʔϧυ͕ଓ͘

༻ޠΛ͓͑͞Α͏ NBSLXPSE ͢΂ͯͷPCKFDUIFBEFSͷ࠷ॳͷϫʔυ ௨ৗɺಉظঢ়ଶͱࣝผϋογϡίʔυΛؚΉϏοτϑΟʔϧυͷηοτ ಉظؔ࿈৘ใ΁ͷϙΠϯλͰ΋͋Δ ($ͷؒɺ($ঢ়ଶϏοτΛؚΉ͜ͱ͕Ͱ͖Δɻ

༻ޠΛ͓͑͞Α͏ LMBTTQPJOUFS ͢΂ͯͷPCKFDUIFBEFSͷ̎൪໨ͷϫʔυ ݩͷΦϒδΣΫτͷϨΠΞ΢τͱಈ࡞Λهड़͢ΔผͷϝλΦϒδΣΫτΛࢦ͢ +BWBΦϒδΣΫτͷ৔߹ɺLMBTTʹ͸$ ελΠϧͷlWUBCMFؚ͕·Ε͍ͯΔ

͓͞Β͍ PPQ +BWBͷΦϒδΣΫτΛද͢ɻ$$ ͷϙΠϯλͰώʔϓ಺ͷҐஔΛࢦ͢ PCKFDUIFBEFS ($͕؅ཧ͢Δ͢΂ͯͷώʔϓΦϒδΣΫτ 001 ͷઌ಄ͷڞ௨ߏ଄ NBSLXPSE ͢΂ͯͷPCKFDUIFBEFSͷ࠷ॳͷϫʔυɻಉظ΍($ͷ৘ใΛ࣋ͭ
LMBTTQPJOUFS ͢΂ͯͷPCKFDUIFBEFSͷ̎൪໨ͷϫʔυɻ+BWBΦϒδΣΫτͷ৔߹lWUBCMFzؚ͕·ΕΔ

001 _mark _klass Fields 32-bit cpu 64-bit cpu 4 byte
8 byte 4 byte 8 byte -XX:ObjectAlignmentInBytes=8 ͢΂ͯͷΦϒδΣΫτ͸όΠτڥքʹ഑ஔ͞ΕΔ PCKFDUIFBEFS NBSLXPSE LMBTTQPJOUFS

java.lang.Object object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 16
(object header) N/A Instance size: 16 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total +0-Ͱग़ྗͯ͠Έͨ݁Ռ new Object() すると、64-bit cpu では 16 byte 消費することになる 001

PPQ%FTD JOTUBODF0PQ%FTDʜ+BWBΦϒδΣΫτͷ001 BSSBZ0PQ%FTDʜ഑ྻΛද͢001ͷ਌ PCK"SSBZ0PQ%FTDʜ഑ྻΦϒδΣΫτͷ001 UZQF"SSBZ0PQ%FTDʜϓϦϛςΟϒͷ഑ྻͷ001

$PNQSFTTFE001 CJUϚγϯͰ΋ΦϒδΣΫτͷΞυϨεΛѹॖ͢Δ +BWBώʔϓͷ࢖༻ྔΛઅ໿ ώʔϓͷϕʔεΞυϨε͔ΒͷΦϑηοτΛར༻ ѹॖ001͸+BWBV͔ΒσϑΥϧτͰΦϯ 996TF$PNQSFTTFE0PQTͰ੾Δ͜ͱ͕Ͱ͖Δ http://www.oracle.com/technetwork/jp/articles/java/compressedoops-427542-ja.html ৄ͘͠͸ KBWB99 1SJOU'MBHT'JOBM)FMMPcHSFQ6TF$PNQSFTTFE0PQTʜ֬ೝ
KBWB99 6OMPDL%JBHOPTUJD7.0QUJPOT99 1SJOU$PNQSFTTFE0PQT.PEF)FMMPʜৄࡉ৘ใग़ྗ

,MBTT 001ͷϔομͷҰ෦ ,MBTT͸Ϋϥεͷ.FUBTQBDF಺ͷ؅ཧϙΠϯλΛද͢ CJUϚγϯͰCZUFɺCJUϚγϯͰCZUF࢖༻͢ΔʢѹॖͰ͖Δʣ http://otndnld.oracle.co.jp/ondemand/javaday2014/pdf/C2-JavaDay-304328.pdf

,MBTTϙΠϯλͷѹॖ $PNQSFTTFE001ͱಉ͡Α͏ʹ+BWB)FBQΛઅ໿ $PNQSFTTFE$MBTT1PJOUFS4QBDF $$14 ͱ͍͏ϝϞϦΤϦΞΛ༻ҙ *OTUBODF,MBTT "SSBZ,MBTT W5BCMFͳͲύϑΥʔϚϯεʹӨڹ͢ΔΫϥε ͷΈ֨ೲ͠ɺͦΕҎ֎͸.FUBTQBDFʹ֨ೲʢϝιουɺίϯελϯτϓʔϧͳͲʣ

,MBTT ,MBTT͸͞·͟·ͳܕ৘ใͷந৅తͳجఈΫϥε

*OTUBODF,MBTTʜܕΫϥεͷΠϯελϯε *OTUBODF.JSSPS,MBTTʜKBWBMBOH$MBTTΛද͢ *OTUBODF$MBTT-PBEFS,MBTTʜ*OTUBODF,MBTTͷΫϥεϩʔμ༻ *OTUBODF3FG,MBTTʜKBWBMBOHSFG3FGFSFODFͷαϒΫϥε ɹɹɹɹɹɹɹɹɹɹ TPGUXFBLpOBMQIBOUPN ,MBTT

"SSBZ,MBTTʜ഑ྻΛද͢਌Ϋϥε 0CK"SSBZ,MBTTʜΦϒδΣΫτͷ഑ྻͷΫϥε 5ZQF"SSBZ,MBTTʜϓϦϛςΟϒͷ഑ྻͷΫϥε ,MBTT

001ͱ,MBTTͷؔ܎ InstanceOop _klass InstanceKlass InstanceKlass _super *OTUBODF0PQTUS ,MBTT4USJOH ,MBTT0CKFDU Metaspace
InstanceOop PPQ$MBTT4USJOH _java_mirror Java Heap String str = “hoge”; InstanceMirrorKlass _klass

.BSL ($ɺಉظԽͷͨΊͷ৘ใΛ΋͍ͬͯΔ CJUϚγϯͰ͸όΠτɺCJUϚγϯͰ͸όΠτͷ௕͞ʹͳΔ .BSL͸ϙΠϯλͰ͸ͳ͘σʔλߏ଄

.BSL hash age CJU CJU unused:25 hash:31 -->| unused:1 age:4
biased_lock:1 lock:2 (normal object) hash:25 ------------>| age:4 biased_lock:1 lock:2 (normal object) src/share/vm/oops/markOop.hpp ʢྫʣ6OMPDLFE ޙड़ ͷ.BSLͷϝϞϦߏ଄ hash age

.BSL .BSLͷঢ়ଶ͸ओʹҎԼͷ̑ͭ ɹ#JBTFE ɹ6OMPDLFE લड़ͷOPSNBMPCKFDU ɹ-JHIUXFJHIU-PDLFE ɹ)FBWZXFJHIU-PDLFE ɹ.BSLFEʢ($ͷΈʣ https://wiki.openjdk.java.net/display/HotSpot/Synchronization
Mark には5種類のデータ構造がある

#JBTFE-PDLJOH جຊϩοΫͰ͸ճͷϩοΫͰ࠷௿ճͷ$"4໋ྩΛ࢖͏ #JBTFE-PDLJOHͷίϯηϓτ ɹɾ͋ΔεϨου͔ΒϩοΫ͞ΕͨΦϒδΣΫτ͸ ɹɹಉ͡εϨου͔ΒϩοΫ͞ΕΔ܏޲͕͋Δ ɹɾΦϒδΣΫτͷதʹεϨου৘ใΛຒΊࠐΜͰಛఆͷεϨουʹ ภ͍ͬͯΔ CJBTFE ͜ͱΛࣔ͢ɻͦΕʹΑΓͦͷεϨου͔Βͷ ϩοΫ͸$"4໋ྩͳ͠Ͱߦ͏͜ͱ͕Ͱ͖Δ

.BSLͷঢ়ଶ#JBTFE ΦϒδΣΫτׂ͕Γ౰ͯΒΕΔ #JBTFE-PDLJOH͸+BWB͔ΒσϑΥϧτͳͷͰCJBTBCMFPCKFDUʹͳΔ ϩοΫ͢ΔͱUISFBE*%͕ઃఆ͞ΕΔ CJBTFEPCKFDU
SFCJBT͢ΔͱCJBTBCMFPCKFDUʹ໭Δ ҰఆपظͰSFCJBT͢ΔΒ͍͠ ଞͷεϨουͰར༻͞ΕΔͱجຊϩοΫʹͳΔ #JBTFE-PDLJOH͕ղআ͞ΕΔ 0 epoch age 1 01 thread ID epoch age 1 01 JOJUJBMMPDL SFCJBT CJBTBCMFPCKFDU CJBTFEPCKFDU

.BSLͷঢ়ଶ hash code age 0 01 pointer to lock record
00 #JBTFE-PDLJOH͕ར༻Ͱ͖ͳ͍৔߹͸جຊϩοΫͷϓϩηεʹͳΔ جຊϩοΫͰϩοΫ͢Δͱ5IJO-PDL͕͔͔Δ εϨου͕͢ͰʹͦͷΦϒδΣΫτͷϩοΫΛ͍࣋ͬͯΔ৔߹͸3FDVSTJWF-PDLʹͳΔ ฒߦॲཧͳͲͰෳ਺ͷҟͳΔεϨου͔Βಉ͡ΦϒδΣΫτʹରͯ͠ ಉ࣌ʹಉظॲཧ͕ߦΘΕΔͱ*OqBUF-PDLʹͳΔ pointer to heavyweight monitor 10 6OMPDLFE -JHIUXFJHIU-PDLFE )FBWZXFJHIU-PDLFE 5IJO-PDL *OqBUF-PDL ʜVOMPDLFE ʜMPDLFE ʜNPOJUPS

·ͱΊ ͜ΕΒͷ༻ޠ͸͢΂֮ͯ͑Δඞཁ͸ͳ͍ ग़͖ͯͨͱ͖ʹௐ΂Ε͹͍͍ ࠓ೔ग़͖ͯͨ୯ޠ͸೔ৗۀ຿Ͱ͸࢖༻͠·ͤΜ

ϝϞϦϨΠΞ΢τ

ϝϞϦϨΠΞ΢τ _mark _klass Fields 32-bit cpu 64-bit cpu 4 byte
8 byte 4 byte 8 byte -XX:ObjectAlignmentInBytes=8 ͢΂ͯͷΦϒδΣΫτ͸όΠτڥքʹ഑ஔ͞ΕΔ PCKFDUIFBEFS NBSLXPSE LMBTTQPJOUFS

java.lang.Object object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 16
(object header) N/A Instance size: 16 bytes Space losses: 0 bytes internal + 0 bytes external = 0 bytes total ѹॖ001ͳ͠ java.lang.Object object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 12 (object header) N/A 12 4 (loss due to the next object alignment) Instance size: 16 bytes Space losses: 0 bytes internal + 4 bytes external = 4 bytes total ѹॖ001͋Γ ϝϞϦϨΠΞ΢τ

001ϔομͷޙʹΫϥεϑΟʔϧυ͕ଓ͘ ϝϞϦઅ໿ͷͨΊʹ+7.͸ఆٛ͞Εͨॱ൪Ͱ͸ͳ͘ฒͼସ͑Λߦ͏ ϑΟʔϧυ͸جຊతʹ࣍ͷ༏ઌॱҐͰϝϞϦʹߏ੒͢Δ 1 double, long 8 2 int, ﬂoat
4 3 short, char 2 4 boolean, byte 1 5 ΦϒδΣΫτࢀর 8 (64bit) ϝϞϦϨΠΞ΢τ

class A { byte a; int c; short d; long
e; Object f; } ᶃ ᶄ ᶆ ᶅ ᶇ jol.samples.A object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 16 (object header) N/A 16 8 long D.e N/A 24 4 int D.c N/A 28 2 short D.d N/A 30 1 byte D.a N/A 31 1 (alignment/padding gap) 32 8 java.lang.Object D.f N/A Instance size: 40 bytes Space losses: 1 bytes internal + 0 bytes external = 1 bytes total ᶃ ᶄ ᶅ ᶆ ᶇ ѹॖ001ͳ͠ ϝϞϦϨΠΞ΢τ

class A { byte a; int c; short d; long
e; Object f; } ᶃ ᶄ ᶆ ᶅ ᶇ jol.samples.A object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 12 (object header) N/A 12 4 int D.c N/A 16 8 long D.e N/A 24 2 short D.d N/A 26 1 byte D.a N/A 27 1 (alignment/padding gap) 28 4 java.lang.Object D.f N/A Instance size: 32 bytes Space losses: 1 bytes internal + 0 bytes external = 1 bytes total ᶃ ᶄ ᶅ ᶆ ᶇ ѹॖ001͋Γ ϝϞϦϨΠΞ΢τ

αϒΫϥεͷϝϞϦϨΠΞ΢τ ɹ֊૚͕ҟͳΔΫϥεͷϑΟʔϧυ͸ࠞ߹͠ͳ͍ ɹ਌ΫϥεͷϑΟʔϧυ͕ઌʹ͖ͯɺαϒΫϥεͷϑΟʔϧυ͕ͦͷޙʹ͘Δ ϝϞϦϨΠΞ΢τ

class A { byte a; } class B extends A
{ long b; short c; byte d; } jol.samples.B object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 12 (object header) N/A 12 1 byte A.a N/A 13 3 (alignment/padding gap) 16 8 long B.b N/A 24 2 short B.c N/A 26 1 byte B.d N/A 27 5 (loss due to the next object alignment) Instance size: 32 bytes Space losses: 3 bytes internal + 5 bytes external = 8 bytes total ϝϞϦϨΠΞ΢τ

String str = “Hello World”; ͜ͷ+BWBΦϒδΣΫτ͸ԿCZUFͷϝϞϦΛফඅ͢Δ͔ ϝϞϦϨΠΞ΢τ

+0-Ͱ$MBTT-BZPVUΛΈͯΈΔ String str = “Hello World”; System.out.println(ClassLayout.parseInstance(str).toPrintable()); ϝϞϦϨΠΞ΢τ

+0-Ͱ$MBTT-BZPVUΛΈͯΈΔ java.lang.String object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0
4 (object header) 01 00 00 00 4 4 (object header) 00 00 00 00 8 4 (object header) da 02 00 f8 12 4 char[] String.value [H, e, l, l, o, , W, o, r, l, d] 16 4 int String.hash 0 20 4 (loss due to the next object alignment) Instance size: 24 bytes Space losses: 0 bytes internal + 4 bytes external = 4 bytes total ϝϞϦϨΠΞ΢τ

String str = “Hello World”; System.out.println(GraphLayout.parseInstance(str).toPrintable()); +0-ͰΠϯελϯεͷ(SBQI-BZPVUΛΈͯΈΔ ϝϞϦϨΠΞ΢τ

+0-ͰΠϯελϯεͷ(SBQI-BZPVUΛΈͯΈΔ java.lang.String@532760d8d object externals: ADDRESS SIZE TYPE PATH VALUE 76b98fb58
24 java.lang.String (object) 76b98fb70 40 [C .value [H, e, l, l, o, , W, o, r, l, d] DIBSͷ഑ྻͰCZUFফඅ͍ͯ͠Δ ϝϞϦϨΠΞ΢τ

[C object internals: OFFSET SIZE TYPE DESCRIPTION VALUE 0 4
(object header) 01 00 00 00 4 4 (object header) 00 00 00 00 8 4 (object header) 41 00 00 f8 12 4 (object header) 0b 00 00 00 16 22 char [C.<elements> N/A 38 2 (loss due to the next object alignment) Instance size: 40 bytes Space losses: 0 bytes internal + 2 bytes external = 2 bytes total ͜ͷDIBSͷ഑ྻͷ$MBTT-BZPVUΛΈͯΈΔ <) F M M P 8 P S M E>͸ཁૉ਺YC ഑ྻͷ௕͕͞ϔομʹઃఆ͞ΕΔ ϝϞϦϨΠΞ΢τ

String str = “Hello World”; ͜ͷ+BWBΦϒδΣΫτ͸ԿCZUFͷϝϞϦΛফඅ͢Δ͔ 4USJOHCZUF DIBS<>CZUF ߹ܭɿCZUF ϝϞϦϨΠΞ΢τ
_mark _klass char[] String.value int String.hash padding _mark _klass length char [C.<elements> padding CZUF CZUF 4USJOH DIBS<>

+7.ͷιʔείʔυ

+7.ͷιʔείʔυ ιʔείʔυͷϦϙδτϦʢ.FSDVSJBMʣ http://hg.openjdk.java.net/ KEL KEL KELV KEL KELV KEL KEL

+7.ͷιʔείʔυ IPUTQPU IPUTQPUຊମ MJCKWN Λ࡞ΔͨΊͷ.BLFpMFͱιʔείʔυΛೲΊͨσΟϨΫτϦ KEL MJCKWNҎ֎ͷϥΠϒϥϦΛ࡞ΔͨΊͷϑΝΠϧ .BLFpMF ιʔείʔυ ٴͼ+BWB
ͷඪ४ϥΠϒϥϦ༻ͷιʔείʔυ KBWBϑΝΠϧ ΛೲΊͨσΟϨΫτϦ MBOHUPPMT MBOHVBHFUPPMT KBWBD KBWBEPD KBWBI KBWBQ BQU౳ Λ࡞ΔͨΊͷ.BLFpMFͱιʔ είʔυΛೲΊͨσΟϨΫτϦ http://hsmemo.github.io/articles/noazh2rR49.html ˞ଞʹ΋ͨ͘͞Μ͋Δ

+7.ͷιʔείʔυ PPQT +BWBͷΦϒδΣΫτ؅ཧ +BWBΦϒδΣΫτͷ಺෦දݱ ʹؔ͢Διʔείʔυ SVOUJNF )PU4QPUͷϥϯλΠϜػೳʹؔ͢Διʔείʔυ NFNPSZ +BWBώʔϓ؅ཧʹؔ͢Διʔείʔυ DMBTTpMF
ΫϥεϑΝΠϧ؅ཧ ΫϥεϩʔσΟϯάॲཧ΋ؚΉ ʹؔ͢Διʔείʔυ JOUFSQSFUFS ΠϯλʔϓϦλؔ࿈ͷιʔείʔυ QSJNT +/*΍+7.5* TVONJTDVOTBGF౳ʹؔ͢Διʔείʔυ http://hsmemo.github.io/articles/nopoim3uPN.html IPUTQPUTSDTIBSFWNҎԼ ˞ଞʹ΋ͨ͘͞Μ͋Δ

+7.ͷىಈ

+7.ͷىಈ )PU4QPU3VOUJNF0WFSWJFX http://openjdk.java.net/groups/hotspot/docs/RuntimeOverview.html ىಈ࣌ͷৄ͍͠ॲཧ͸͜͜ʹॻ͍ͯ͋Δ http://tango238.github.io/jvm/hotspot-runtime-overview_translated.html ʢҰ෦෼͚ͩҎલ຋༁͍ͯ͠Δʣ

+7.ͷىಈ ίϚϯυϥΠϯҾ਺Λղੳ͢ΔɻͦͷଞͷҾ਺͸7.ʹ౉͞ΕΔ ώʔϓαΠζ͓ΑͼελοΫαΠζΛઃఆ͢Δ +7.λΠϓ͓Αͼ؀ڥม਺Λઃఆ͢Δ
.BJOΫϥεΛಡΈࠐΉ ৽͘͠࡞੒͞ΕͨεϨου಺Ͱ7.Λ࡞੒͢Δ 7.͕ॳظԽ͞Εɺ.BJO$MBTT͔ΒϝΠϯϝιουͷଐੑΛऔಘ͢Δ ϝΠϯϝιουΛݺͼग़͢ ϝΠϯϝιου࣮ߦ׬ྃޙɺൃੜͨ͠ྫ֎ΛνΣοΫɺFYJUεςʔλεΛฦ٫ ϝΠϯεϨουΛσλονɻσλον͢ΔͱεϨουΧ΢ϯτΛσΫϦϝϯτ͢Δ ɹɹ͜ΕʹΑΓ%FTUSPZ+BWB7.Λ҆શʹݺͼग़͢͜ͱ͕Ͱ͖Δ +/*@$SFBUF+BWB7. IPUTQPUTSDTIBSFWNQSJNFTKOJDQQ ͋ͨΓ͕ಛʹॏཁ

+7.ͷىಈ ίϚϯυϥΠϯҾ਺Λղੳ͢ΔɻͦͷଞͷҾ਺͸7.ʹ౉͞ΕΔ ώʔϓαΠζ͓ΑͼελοΫαΠζΛઃఆ͢Δ +7.λΠϓ͓Αͼ؀ڥม਺Λઃఆ͢Δ
.BJOΫϥεΛಡΈࠐΉ ৽͘͠࡞੒͞ΕͨεϨου಺Ͱ7.Λ࡞੒͢Δ 7.͕ॳظԽ͞Εɺ.BJO$MBTT͔ΒϝΠϯϝιουͷଐੑΛऔಘ͢Δ ϝΠϯϝιουΛݺͼग़͢ ϝΠϯϝιου࣮ߦ׬ྃޙɺൃੜͨ͠ྫ֎ΛνΣοΫɺFYJUεςʔλεΛฦ٫ ϝΠϯεϨουΛσλονɻσλον͢ΔͱεϨουΧ΢ϯτΛσΫϦϝϯτ͢Δ ɹɹ͜ΕʹΑΓ%FTUSPZ+BWB7.Λ҆શʹݺͼग़͢͜ͱ͕Ͱ͖Δ +/*@$SFBUF+BWB7. IPUTQPUTSDTIBSFWNQSJNFTKOJDQQ ͋ͨΓ͕ಛʹॏཁ ͜ͷ΁Μ·Ͱʢ؆ུԽͨ͠ʣιʔείʔυΛ௥ͬͯΈ͍ͨͱࢥ͍·͢

+7.ͷىಈ ΤϯτϦϙΠϯτʢKELVEFWʣ http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/ﬁle/3462d04401ba/src/share/bin/main.c int main(int argc, char **argv) { int
margc; char** margv; const jboolean const_javaw = JNI_FALSE; margc = argc; margv = argv; return JLI_Launch(margc, margv, sizeof(const_jargs) / sizeof(char *), const_jargs, sizeof(const_appclasspath) / sizeof(char *), const_appclasspath, FULL_VERSION, DOT_VERSION, (const_progname != NULL) ? const_progname : *margv, (const_launcher != NULL) ? const_launcher : *margv, (const_jargs != NULL) ? JNI_TRUE : JNI_FALSE, const_cpwildcard, const_javaw, const_ergo_class); }

+7.ͷىಈ ίϚϯυϥΠϯҾ਺Λղੳ͢ΔɻͦͷଞͷҾ਺͸7.ʹ౉͞ΕΔ http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/ﬁle/e74259b3eadc/src/share/bin/java.c int JLI_Launch(…) { InitLauncher(javaw); // 初期化 SelectVersion(argc,
argv, &main_class); // JREバージョンの選択 CreateExecutionEnvironment(…); // JVMタイプおよび環境変数を設定 // JVMをロード。ifn->CreateJavaVM = JNI_CreateJavaVM が設定される if (!LoadJavaVM(jvmpath, &ifn)) { return(6); } // コマンドライン引数を解析 if (!ParseArguments(&argc, &argv, &mode, &what, &ret, jrepath)) { return(ret); } SetJavaCommandLineProp(what, argc, argv); SetJavaLauncherProp(); SetJavaLauncherPlatformProps(); return JVMInit(&ifn, threadStackSize, argc, argv, mode, what, ret); }

+7.ͷىಈ ώʔϓαΠζ͓ΑͼελοΫαΠζΛઃఆ͢Δ http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/ﬁle/e74259b3eadc/src/share/bin/java.c void AddOption(char *str, void *info) { //
ParseArguments() から実行 if (JLI_StrCCmp(str, "-Xss") == 0) { jlong tmp; if (parse_size(str + 4, &tmp)) { threadStackSize = tmp; } } if (JLI_StrCCmp(str, "-Xmx") == 0) { jlong tmp; if (parse_size(str + 4, &tmp)) { maxHeapSize = tmp; } } if (JLI_StrCCmp(str, "-Xms") == 0) { jlong tmp; if (parse_size(str + 4, &tmp)) { initialHeapSize = tmp; } } }

+7.ͷىಈ +7.λΠϓ͓Αͼ؀ڥม਺ʢ-%@-*#3"3:@1"5)ʣΛઃఆ͢Δ http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/ﬁle/e74259b3eadc/src/solaris/bin/java_md_solinux.c void CreateExecutionEnvironment(...) { SetExecname(*pargv); // 実行ファイル名を設定 if
(!GetJREPath(jrepath, so_jrepath, arch, JNI_FALSE) ) { // 使用するJREを取得 exit(2); } if (ReadKnownVMs(jvmcfg, JNI_FALSE) < 1) { // 指定されたJVMタイプを検索(jvm.cfg) exit(1); } // JVMタイプをチェック (-client, -server を削除) jvmtype = CheckJvmType(pargc, pargv, JNI_FALSE); if (JLI_StrCmp(jvmtype, "ERROR") == 0) { exit(4); } if (!GetJVMPath(jrepath, jvmtype, jvmpath, so_jvmpath, arch, 0 )) { exit(4); } // LD_LIBRARY_PATH を取得 runpath = getenv(LD_LIBRARY_PATH); execve(...); }

+7.ͷىಈ .BJOΫϥεΛಡΈࠐΉ int JNICALL JavaMain(void * _args) { JavaMainArgs *args
= (JavaMainArgs *)_args; InvocationFunctions ifn = args->ifn; // JVMの初期化 if (!InitializeJVM(&vm, &env, &ifn)) { // ifn->CreateJavaVM(JNI_CreateJavaVM)を実行 exit(1); } mainClass = LoadMainClass(env, mode, what); // メインクラスをロード // JavaFXなどでメインクラスがコマンドラインで指定されていない場合 // JARのマニフェストファイルにある Main-Class の名前を読み込む appClass = GetApplicationClass(env); mainID = (*env)->GetStaticMethodID(env, mainClass, "main", "([Ljava/lang/String;)V"); // アプリケーションのコマンドライン引数を設定 mainArgs = CreateApplicationArgs(env, argv, argc); // メインメソッドを実行 (*env)->CallStaticVoidMethod(env, mainClass, mainID, mainArgs); // 例外を捕捉 ret = (*env)->ExceptionOccurred(env) == NULL ? 0 : 1; } http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/ﬁle/e74259b3eadc/src/share/bin/java.c

+7.ͷىಈ ৽͘͠࡞੒͞ΕͨεϨου಺Ͱ7.Λ࡞੒͢Δ int JVMInit(...) { ShowSplashScreen(); return ContinueInNewThread(ifn, threadStackSize, argc,
argv, mode, what, ret); } http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/ﬁle/e74259b3eadc/src/solaris/bin/java_md_solinux.c int ContinueInNewThread(...) { JavaMainArgs args; args.argc = argc; args.argv = argv; args.ifn = *ifn; // 新しいスレッドを作成してメインメソッドを実行 rslt = ContinueInNewThread0(JavaMain, threadStackSize, (void*)&args); return (ret != 0) ? ret : rslt; } http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/ﬁle/e74259b3eadc/src/share/bin/java.c

+7.ͷىಈ Ҏ߱ͷॲཧ͸IPUTQPUTSDTIBSFWNҎԼ http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/ﬁle/259c36bd7aea/src/share/vm/prims/jni.cpp#l5162 ΤϯτϦʔϙΠϯτ +/*@$SFBUF+BWB7. ओཁ෦෼ͷιʔείʔυ http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/ﬁle/259c36bd7aea/src/share/vm/runtime/thread.cpp#l3306 ˠ5ISFBETDSFBUF@WNΛಡΊΕ͹৭ʑΘ͔ͬͯ͘Δͱࢥ͏

int JLI_Launch(int argc, char ** argv, /* main argc, argc
*/ int jargc, const char** jargv, /* java args */ int appclassc, const char** appclassv, /* app classpath */ const char* fullversion, /* full version defined */ const char* dotversion, /* dot version defined */ const char* pname, /* program name */ const char* lname, /* launcher name */ jboolean javaargs, /* JAVA_ARGS */ jboolean cpwildcard, /* classpath wildcard*/ jboolean javaw, /* windows-only javaw */ jint ergo /* ergonomics class policy */ ) { InitLauncher(javaw); // JLI_SetTraceLauncherしてる DumpState(); if (JLI_IsTraceLauncher()) { int i; printf("Command line args:\n"); for (i = 0; i < argc ; i++) { printf("argv[%d] = %s\n", i, argv[i]); } AddOption("-Dsun.java.launcher.diag=true", NULL); } +7.ͷىಈॲཧ·ΘΓͷখωλ

static void DumpState() { if (!JLI_IsTraceLauncher()) return ; printf("Launcher state:\n");
printf("\tdebug:%s\n", (JLI_IsTraceLauncher() == JNI_TRUE) ? "on" : "off"); printf("\tjavargs:%s\n", (_is_java_args == JNI_TRUE) ? "on" : "off"); printf("\tprogram name:%s\n", GetProgramName()); printf("\tlauncher name:%s\n", GetLauncherName()); printf("\tjavaw:%s\n", (IsJavaw() == JNI_TRUE) ? "on" : "off"); printf("\tfullversion:%s\n", GetFullVersion()); printf("\tdotversion:%s\n", GetDotVersion()); printf("\tergo_policy:"); switch(GetErgoPolicy()) { case NEVER_SERVER_CLASS: printf("NEVER_ACT_AS_A_SERVER_CLASS_MACHINE\n"); break; case ALWAYS_SERVER_CLASS: printf("ALWAYS_ACT_AS_A_SERVER_CLASS_MACHINE\n"); break; default: printf("DEFAULT_ERGONOMICS_POLICY\n"); } } +7.ͷىಈॲཧ·ΘΓͷখωλ

+7.ͷىಈॲཧ·ΘΓͷখωλ void JLI_SetTraceLauncher() { if (getenv(JLDEBUG_ENV_ENTRY) != 0) { _launcher_debug
= JNI_TRUE; JLI_TraceLauncher("----%s----\n", JLDEBUG_ENV_ENTRY); } } openjdk/jdk8u/jdk/src/share/bin/jli_util.h 33:#define JLDEBUG_ENV_ENTRY "_JAVA_LAUNCHER_DEBUG"

$ export _JAVA_LAUNCHER_DEBUG=1 $ java Hello ----_JAVA_LAUNCHER_DEBUG---- Launcher state: debug:on
javargs:off program name:java launcher name:java javaw:off fullversion:1.8.0_131-b11 dotversion:1.8 ergo_policy:DEFAULT_ERGONOMICS_POLICY Command line args: argv[0] = /usr/bin/java argv[1] = Hello JRE path is /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre jvm.cfg[0] = ->-server<- jvm.cfg[1] = ->-client<- 6957 micro seconds to parse jvm.cfg Default VM: server ~ +7.ͷىಈॲཧ·ΘΓͷখωλ

·ͱΊ ͜ΕΒͷ༻ޠ͸͢΂֮ͯ͑Δඞཁ͸ͳ͍ ग़͖ͯͨͱ͖ʹௐ΂Ε͹͍͍ ࠓ೔ग़͖ͯͨ୯ޠ͸೔ৗۀ຿Ͱ͸࢖༻͠·ͤΜ ಡΜͰ͍Δͱཪٕ΍಺෦ಈ࡞ʹৄ͘͠ͳͬͯ͘ΔͷͰָ͘͠ͳͬͯ͘Δ

͋Γ͕ͱ͏͍͟͝·ͨ͠ʂ

4ZODISPOJ[BUJPOBOE0CKFDU-PDLJOH )PU4QPUVOEFSUIF)PPE -PDLJOHBOE4ZODISPOJ[BUJPO +BWBΦϒδΣΫτͷϝϞϦߏ଄ &WFSZUIJOH*&WFS-FBSOFE"CPVU+7.1FSGPSNBODF5VOJOH!5XJUUFS +%,+7.*NQSPWFNFOUT ࢀߟࢿྉ https://www.infoscoop.org/blogjp/2014/06/16/java-objects-memory-structure/ https://www.slideshare.net/aszegedi/everything-i-ever-learned-about-jvm-performance-tuning-twitter https://www.slideshare.net/nminoru_jp/jvm-readingsynchronization
https://www.infoq.com/presentations/hotspot-memory-data-structures https://wiki.openjdk.java.net/display/HotSpot/Synchronization http://otndnld.oracle.co.jp/ondemand/javaday2014/pdf/C2-JavaDay-304328.pdf

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