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arturmkrtchyan/ObjectHeader32.txt

Last active April 8, 2024 02:03
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Java Object Header
Raw
ObjectHeader32.txt
|----------------------------------------------------------------------------------------|--------------------|
| Object Header (64 bits) | State |
|-------------------------------------------------------|--------------------------------|--------------------|
| Mark Word (32 bits) | Klass Word (32 bits) | |
|-------------------------------------------------------|--------------------------------|--------------------|
| identity_hashcode:25 | age:4 | biased_lock:1 | lock:2 | OOP to metadata object | Normal |
|-------------------------------------------------------|--------------------------------|--------------------|
| thread:23 | epoch:2 | age:4 | biased_lock:1 | lock:2 | OOP to metadata object | Biased |
|-------------------------------------------------------|--------------------------------|--------------------|
| ptr_to_lock_record:30 | lock:2 | OOP to metadata object | Lightweight Locked |
|-------------------------------------------------------|--------------------------------|--------------------|
| ptr_to_heavyweight_monitor:30 | lock:2 | OOP to metadata object | Heavyweight Locked |
|-------------------------------------------------------|--------------------------------|--------------------|
| | lock:2 | OOP to metadata object | Marked for GC |
|-------------------------------------------------------|--------------------------------|--------------------|
Raw
ObjectHeader64.txt
|------------------------------------------------------------------------------------------------------------|--------------------|
| Object Header (128 bits) | State |
|------------------------------------------------------------------------------|-----------------------------|--------------------|
| Mark Word (64 bits) | Klass Word (64 bits) | |
|------------------------------------------------------------------------------|-----------------------------|--------------------|
| unused:25 | identity_hashcode:31 | unused:1 | age:4 | biased_lock:1 | lock:2 | OOP to metadata object | Normal |
|------------------------------------------------------------------------------|-----------------------------|--------------------|
| thread:54 | epoch:2 | unused:1 | age:4 | biased_lock:1 | lock:2 | OOP to metadata object | Biased |
|------------------------------------------------------------------------------|-----------------------------|--------------------|
| ptr_to_lock_record:62 | lock:2 | OOP to metadata object | Lightweight Locked |
|------------------------------------------------------------------------------|-----------------------------|--------------------|
| ptr_to_heavyweight_monitor:62 | lock:2 | OOP to metadata object | Heavyweight Locked |
|------------------------------------------------------------------------------|-----------------------------|--------------------|
| | lock:2 | OOP to metadata object | Marked for GC |
|------------------------------------------------------------------------------|-----------------------------|--------------------|
Raw
ObjectHeader64Coops.txt
|--------------------------------------------------------------------------------------------------------------|--------------------|
| Object Header (96 bits) | State |
|--------------------------------------------------------------------------------|-----------------------------|--------------------|
| Mark Word (64 bits) | Klass Word (32 bits) | |
|--------------------------------------------------------------------------------|-----------------------------|--------------------|
| unused:25 | identity_hashcode:31 | cms_free:1 | age:4 | biased_lock:1 | lock:2 | OOP to metadata object | Normal |
|--------------------------------------------------------------------------------|-----------------------------|--------------------|
| thread:54 | epoch:2 | cms_free:1 | age:4 | biased_lock:1 | lock:2 | OOP to metadata object | Biased |
|--------------------------------------------------------------------------------|-----------------------------|--------------------|
| ptr_to_lock_record | lock:2 | OOP to metadata object | Lightweight Locked |
|--------------------------------------------------------------------------------|-----------------------------|--------------------|
| ptr_to_heavyweight_monitor | lock:2 | OOP to metadata object | Heavyweight Locked |
|--------------------------------------------------------------------------------|-----------------------------|--------------------|
| | lock:2 | OOP to metadata object | Marked for GC |
|--------------------------------------------------------------------------------|-----------------------------|--------------------|
@tianshuang
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Awesome !

@duqicauc
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非常好

@soyona
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soyona commented Jul 16, 2018

Awesome!!!

@turf00
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turf00 commented Aug 20, 2018

Magic thanks!

@qeesung
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qeesung commented Nov 13, 2018

Awesome!!! Thx :-)

@neuSnail
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neuSnail commented Apr 4, 2019

thanks �a lot , this is the most clear form I have ever seen especially for 64-bit

@Mehraj123
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Love it

@plotor
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plotor commented Jun 29, 2019

Nice~

@kaiattrib
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thanks 😆

@cjwk
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cjwk commented Dec 16, 2019

Love it

@eunrui
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eunrui commented Jun 2, 2020

Thanks！

@ethan-lau
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thanks

@WillfordZhan
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Thanks！

@stardustman
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Thanks

@lgqaozora
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Thanks!!

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ghost commented Jun 11, 2021

Awesome ～～～

@strogiyotec
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Why hashcode takes 31 bite ? Hashcode in Java is an int which is 4 bytes or 32 bits . Did I miss something ?

@tianshuang
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Your previous blog can’t be accessed. I bookmarked your article before, address: http://arturmkrtchyan.com/java-object-header.

@stardustman
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is multi-byte value use little-endian?

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