讲一下 Java 中的 Monitor。
对象头
以 32 为虚拟机为例。
普通对象
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| |------------------------------------------|
| Object Header(64 bits) |
|------------------------------------------|
| | |
| Mark Word(32 bits)| Klass Word(32 bits) |
| | |
|------------------------------------------|
|
Mark Word
下面的 state 代表 4 种状态，而 Mark Word 一共是 32bits
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| |-----------------------------------------------|-------------------|
| Mark Word(32 bits) | State |
|-------------------------------------------------------------------|
| hashcode: 25 |age: 4 | biased_lock:0| 01| Normal |
|-------------------------------------------------------------------|
| thread:23 |epoch:2 |age: 4 | biased_lock:1| 01| Biased |
|-------------------------------------------------------------------|
| ptr_to_lock_record: 30 | 00| Lightweight Locked|
|-------------------------------------------------------------------|
| ptr_to_heavyweight_monitor:30| 10| Heavyweight Locked|
|-------------------------------------------------------------------|
| | 11| Marker for GC |
|-------------------------------------------------------------------|
|
biased_locked 是否启用偏向锁Lightweight 00
Heavyweight 10
这个状态要结合
数组对象
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| |---------------------------------------------------------------------|
| Object Header(96 bits) |
|---------------------------------------------------------------------|
| | | |
| Mark Word(32 bits)| Klass Word(32 bits) | array length (32 bits) |
| | | |
|---------------------------------------------------------------------|
|
