开启掘金成长之旅！这是我参与「掘金日新计划 · 12 月更文挑战」的第17天，点击查看活动详情
1.偏向锁竞争
这次讲的例子是上一篇的略微更改，是把A线程睡眠时间移动到外部，A线程释放锁并不结束线程，此时B线程进行竞争会产生批量重偏向问题。
public class SyncSyncLockRelease2 {
public static void main(String[] args) throws InterruptedException {
List<Object> list = new ArrayList<>();
for(int i = 0; i < 20; i++) {
Object obj = new Object(); //创建20个object对象
list.add(obj);
System.out.println("====A 加锁前"+i+"==="+ClassLayout.parseInstance(obj).toPrintable());
Thread A = new Thread() {
@SneakyThrows
@Override
public void run() { //创建了20条线程
synchronized (obj) {
System.out.println("===A 加锁中==="+ClassLayout.parseInstance(obj).toPrintable());
}
Thread.sleep(20000);
}
};
A.start();
}
Thread.sleep(200);
for(int i = 0; i < 20; i++) {
Object obj = list.get(i);
System.out.println("====B加锁前"+i+"==="+ClassLayout.parseInstance(obj).toPrintable());
Thread B = new Thread() {
@SneakyThrows
@Override
public void run() {
synchronized (obj) {
System.out.println("====B加锁中==="+ClassLayout.parseInstance(obj).toPrintable());
Thread.sleep(1000);
}
}
};
B.start();
}
Thread.sleep(5000);
synchronized (list.get(19)) {
System.out.println("===再次加锁==="+ClassLayout.parseInstance(list.get(19)).toPrintable());
}
System.out.println("===新对象=="+ClassLayout.parseInstance(new Object()).toPrintable());
}
}
效果如下：
====A 加锁前0===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前1===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 e8 57 22 (00000101 11101000 01010111 00100010) (576186373)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前2===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 70 59 22 (00000101 01110000 01011001 00100010) (576286725)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前3===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 28 59 22 (00000101 00101000 01011001 00100010) (576268293)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前4===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 38 59 22 (00000101 00111000 01011001 00100010) (576272389)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前5===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 d8 59 22 (00000101 11011000 01011001 00100010) (576313349)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前6===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 30 5a 22 (00000101 00110000 01011010 00100010) (576335877)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前7===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 f0 5a 22 (00000101 11110000 01011010 00100010) (576385029)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前8===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 50 5b 22 (00000101 01010000 01011011 00100010) (576409605)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前9===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 60 5b 22 (00000101 01100000 01011011 00100010) (576413701)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前10===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 c8 2e 18 (00000101 11001000 00101110 00011000) (405719045)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前11===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 90 2e 18 (00000101 10010000 00101110 00011000) (405704709)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前12===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 60 2e 18 (00000101 01100000 00101110 00011000) (405692421)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前13===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 68 2e 18 (00000101 01101000 00101110 00011000) (405694469)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前14===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 b8 5d 22 (00000101 10111000 01011101 00100010) (576567301)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前15===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 f0 5d 22 (00000101 11110000 01011101 00100010) (576581637)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前16===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 a8 5d 22 (00000101 10101000 01011101 00100010) (576563205)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前17===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 c0 5d 22 (00000101 11000000 01011101 00100010) (576569349)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前18===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 a0 5d 22 (00000101 10100000 01011101 00100010) (576561157)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====A 加锁前19===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 00 00 (00000101 00000000 00000000 00000000) (5)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 e8 5d 22 (00000101 11101000 01011101 00100010) (576579589)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===A 加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 00 5e 22 (00000101 00000000 01011110 00100010) (576585733)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前0===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 e8 57 22 (00000101 11101000 01010111 00100010) (576186373)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前1===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 70 59 22 (00000101 01110000 01011001 00100010) (576286725)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前2===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 28 59 22 (00000101 00101000 01011001 00100010) (576268293)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) e0 ee e9 23 (11100000 11101110 11101001 00100011) (602533600)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) a0 f2 f9 23 (10100000 11110010 11111001 00100011) (603583136)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前3===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 38 59 22 (00000101 00111000 01011001 00100010) (576272389)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 10 f3 09 24 (00010000 11110011 00001001 00100100) (604631824)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前4===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 d8 59 22 (00000101 11011000 01011001 00100010) (576313349)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) a0 f3 19 24 (10100000 11110011 00011001 00100100) (605680544)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前5===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 30 5a 22 (00000101 00110000 01011010 00100010) (576335877)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前6===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 f0 5a 22 (00000101 11110000 01011010 00100010) (576385029)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) b0 f6 39 24 (10110000 11110110 00111001 00100100) (607778480)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 60 f0 29 24 (01100000 11110000 00101001 00100100) (606728288)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前7===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 50 5b 22 (00000101 01010000 01011011 00100010) (576409605)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 90 f2 49 24 (10010000 11110010 01001001 00100100) (608826000)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前8===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 60 5b 22 (00000101 01100000 01011011 00100010) (576413701)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 70 f2 59 24 (01110000 11110010 01011001 00100100) (609874544)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前9===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 c8 2e 18 (00000101 11001000 00101110 00011000) (405719045)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) a0 f4 69 24 (10100000 11110100 01101001 00100100) (610923680)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前10===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 90 2e 18 (00000101 10010000 00101110 00011000) (405704709)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 60 f5 79 24 (01100000 11110101 01111001 00100100) (611972448)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前11===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 60 2e 18 (00000101 01100000 00101110 00011000) (405692421)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) a0 ee 89 24 (10100000 11101110 10001001 00100100) (613019296)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前12===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 68 2e 18 (00000101 01101000 00101110 00011000) (405694469)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 00 f3 99 24 (00000000 11110011 10011001 00100100) (614068992)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前13===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 b8 5d 22 (00000101 10111000 01011101 00100010) (576567301)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 30 f3 a9 24 (00110000 11110011 10101001 00100100) (615117616)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前14===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 0d f0 5d 22 (00001101 11110000 01011101 00100010) (576581645)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) a0 f7 b9 24 (10100000 11110111 10111001 00100100) (616167328)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前15===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 0d a8 5d 22 (00001101 10101000 01011101 00100010) (576563213)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 59 5f 22 (00000101 01011001 01011111 00100010) (576674053)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 a1 5f 22 (00000101 10100001 01011111 00100010) (576692485)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前16===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 0d c0 5d 22 (00001101 11000000 01011101 00100010) (576569357)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前17===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 0d a0 5d 22 (00001101 10100000 01011101 00100010) (576561165)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 41 5f 22 (00000101 01000001 01011111 00100010) (576667909)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前18===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 0d e8 5d 22 (00001101 11101000 01011101 00100010) (576579597)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 b1 5f 22 (00000101 10110001 01011111 00100010) (576696581)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁前19===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 0d 00 5e 22 (00001101 00000000 01011110 00100010) (576585741)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 71 5f 22 (00000101 01110001 01011111 00100010) (576680197)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
====B加锁中===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 69 5f 22 (00000101 01101001 01011111 00100010) (576678149)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===再次加锁===java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) c8 f5 9a 02 (11001000 11110101 10011010 00000010) (43709896)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
===新对象==java.lang.Object object internals:
OFFSET SIZE TYPE DESCRIPTION VALUE
0 4 (object header) 05 01 00 00 (00000101 00000001 00000000 00000000) (261)
4 4 (object header) 00 00 00 00 (00000000 00000000 00000000 00000000) (0)
8 4 (object header) e5 01 00 f8 (11100101 00000001 00000000 11111000) (-134217243)
12 4 (loss due to the next object alignment)
Instance size: 16 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
Process finished with exit code 0
2.分析
我们可以看到，20次加锁前的A线程都是偏向锁，并且其他锁信息是0。20次A线程加锁中都是偏向锁并且是记录线程id的。
20次B线程加锁前都是偏向锁，并且记录的是A线程的线程id。然而我们仔细观察可以看到，前15次B线程加锁中是轻量级锁，从第16次开始B线程就是偏向锁，并且再次用对象加锁的时候，还是用的轻量级锁，新对象的加锁还是偏向锁。
这是为什么呢？
A线程获取偏向锁，并且A线程释放了锁，但是A线程并没有死亡还在活跃状态。B线程过来争抢。部分争抢会升级为轻量级锁；部分争抢会依旧保持偏向锁。
批量重偏向： 当我们的一个对象，Object 类，在经过默认 20次的争抢的情况下，会将后边的所有争抢从新偏向争抢的线程。1. 当B线程争抢第 16 次的时候，触发了批量重偏向的阈值；在第十六次以及以后的争抢里，jvm会将线程偏向线程b，因为jvm认为，这个对象更加适合线程B
