javaコード:
import java.lang.ref.WeakReference;
/**
* Created by niewj on 2017/12/17.
*/
public class Main {
public static void main(String[] args) {
User a = new User();
WeakReference b = new WeakReference(a);
int i = 0;
while (true) {
if (b.get() != null) {
i++;
System.out.println("A ！！" + i);
} else {
System.out.println("A--- ----------");
break;
}
}
}
}
class User {}
---
#####1. UseSerialGC
######_(UseSerialGC > Serial + Serial Old)_
`XX:+UseSerialGC -XX:+PrintGC -XX:+PrintGCDetails`
>......
A ！！384384
A ！！384385
A ！！384386
[GC[_**DefNew**_: 68416K->812K(76928K), 0.0032924 secs] 68416K->812K(247872K), 0.0033418 secs] [Times: user=0.02 sys=0.00, real=0.00 secs]
A ！！384387
A--- ----------
Heap
**def new generation** total 76928K, used 2837K [0x0000000700800000, 0x0000000705b70000, 0x0000000753f50000)
_**eden space**_ 68416K, 2% used [0x0000000700800000, 0x00000007009fa518, 0x0000000704ad0000)
_**from space**_ 8512K, 9% used [0x0000000705320000, 0x00000007053eb178, 0x0000000705b70000)
_**to space**_ 8512K, 0% used [0x0000000704ad0000, 0x0000000704ad0000, 0x0000000705320000)
**tenured generation** total 170944K, used 0K [0x0000000753f50000, 0x000000075e640000, 0x00000007fae00000)
the space 170944K, 0% used [0x0000000753f50000, 0x0000000753f50000, 0x0000000753f50200, 0x000000075e640000)
**compacting perm gen** total 21248K, used 3165K [0x00000007fae00000, 0x00000007fc2c0000, 0x0000000800000000)
the space 21248K, 14% used [0x00000007fae00000, 0x00000007fb117430, 0x00000007fb117600, 0x00000007fc2c0000)
No shared spaces configured.
#####2. UseParNew
###### _(UseParNew > ParNew + Serial Old)_
`-XX:+UseParNewGC -XX:+PrintGC -XX:+PrintGCDetails`
> ......
A ！！384386
[GC[_**ParNew**_: 68416K->837K(76928K), 0.0011650 secs] 68416K->837K(247872K), 0.0012095 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
A ！！384387
A--- ----------
Heap
**par new generation** total 76928K, used 3560K [0x0000000700800000, 0x0000000705b70000, 0x0000000753f50000)
_**eden space**_ 68416K, 3% used [0x0000000700800000, 0x0000000700aa8cd8, 0x0000000704ad0000)
_**from space**_ 8512K, 9% used [0x0000000705320000, 0x00000007053f1540, 0x0000000705b70000)
_**to space**_ 8512K, 0% used [0x0000000704ad0000, 0x0000000704ad0000, 0x0000000705320000)
**tenured generation** total 170944K, used 0K [0x0000000753f50000, 0x000000075e640000, 0x00000007fae00000)
the space 170944K, 0% used [0x0000000753f50000, 0x0000000753f50000, 0x0000000753f50200, 0x000000075e640000)
**compacting perm gen** total 21248K, used 3165K [0x00000007fae00000, 0x00000007fc2c0000, 0x0000000800000000)
the space 21248K, 14% used [0x00000007fae00000, 0x00000007fb117430, 0x00000007fb117600, 0x00000007fc2c0000)
No shared spaces configured.
#####3. UseConcMarkSweepGC
###### _(UseConcMarkSweepGC > ParNew + CMS + ..Serial Old)_
`-XX:+UseConcMarkSweepGC -XX:+PrintGC -XX:+PrintGCDetails`
Concurrent Mode Failure, _**Serial Old **_
`-XX:+UseConcMarkSweepGC -XX:+PrintGC -XX:+PrintGCDetails`
> ......
A ！！384385
A ！！384386
[GC[_**ParNew**_: 68416K->836K(76928K), 0.0013431 secs] 68416K->836K(247872K), 0.0014041 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
A ！！384387
A--- ----------
Heap
**par new generation** total 76928K, used 3559K [0x0000000700800000, 0x0000000705b70000, 0x00000007154c0000)
_**eden space**_ 68416K, 3% used [0x0000000700800000, 0x0000000700aa8cd8, 0x0000000704ad0000)
_**from space**_ 8512K, 9% used [0x0000000705320000, 0x00000007053f1130, 0x0000000705b70000)
_**to space**_ 8512K, 0% used [0x0000000704ad0000, 0x0000000704ad0000, 0x0000000705320000)
**concurrent mark-sweep generation** total 170944K, used 0K [0x00000007154c0000, 0x000000071fbb0000, 0x00000007fae00000)
**concurrent-mark-sweep perm gen** total 21248K, used 3166K [0x00000007fae00000, 0x00000007fc2c0000, 0x0000000800000000)
##### 4. UseParallelGC
###### _(UseParallelGC > Parallel Scanvenge + Serial Old)_
`-XX:+UseParallelGC -XX:+PrintGC -XX:+PrintGCDetails`
>A ！！364573
A ！！364574
[GC [_**PSYoungGen**_: 65024K->962K(75264K)] 65024K->970K(245760K), 0.0012285 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
A ！！364575
A--- ----------
Heap
**PSYoungGen** total 75264K, used 3551K [0x00000007ac880000, 0x00000007b1c00000, 0x0000000800000000)
_**eden space**_ 65024K, 3% used [0x00000007ac880000,0x00000007acb070d8,0x00000007b0800000)
_**from space**_ 10240K, 9% used [0x00000007b0800000,0x00000007b08f0bd0,0x00000007b1200000)
_**to space**_ 10240K, 0% used [0x00000007b1200000,0x00000007b1200000,0x00000007b1c00000)
**ParOldGen** total 170496K, used 8K [0x0000000705a00000, 0x0000000710080000, 0x00000007ac880000)
object space 170496K, 0% used [0x0000000705a00000,0x0000000705a02000,0x0000000710080000)
**PSPermGen** total 21504K, used 3165K [0x0000000700800000, 0x0000000701d00000, 0x0000000705a00000)
object space 21504K, 14% used [0x0000000700800000,0x0000000700b17430,0x0000000701d00000)
##### 5. UseParallelOldGC
###### _(UseParallelOldGC > Parallel Scavenge + Parallel Old)_
`-XX:+UseParallelOldGC -XX:+PrintGC -XX:+PrintGCDetails`
> ......
A ！！364574
A ！！364575
[GC [_**PSYoungGen**_: 65024K->874K(75264K)] 65024K->882K(245760K), 0.0020625 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
A ！！364576
A--- ----------
Heap
> **PSYoungGen** total 75264K, used 3463K [0x00000007ac880000, 0x00000007b1c00000, 0x0000000800000000)
_**eden space**_ 65024K, 3% used [0x00000007ac880000,0x00000007acb070d8,0x00000007b0800000)
_**from space**_ 10240K, 8% used [0x00000007b0800000,0x00000007b08dabc0,0x00000007b1200000)
_**to space**_ 10240K, 0% used [0x00000007b1200000,0x00000007b1200000,0x00000007b1c00000)
**ParOldGen** total 170496K, used 8K [0x0000000705a00000, 0x0000000710080000, 0x00000007ac880000)
object space 170496K, 0% used [0x0000000705a00000,0x0000000705a02000,0x0000000710080000)
**PSPermGen** total 21504K, used 3165K [0x0000000700800000, 0x0000000701d00000, 0x0000000705a00000)
object space 21504K, 14% used [0x0000000700800000,0x0000000700b17430,0x0000000701d00000)
##### 6. UseG1GC
###### UseG1GC
`-XX:+UseG1GC -XX:+PrintGC -XX:+PrintGCDetails`
>> ......
A ！！71007
A ！！71008
A ！！71009[GC pause (young), 0.0012627 secs]
[Parallel Time: 1.0 ms, GC Workers: 4]
[GC Worker Start (ms): Min: 922.7, Avg: 922.8, Max: 922.8, Diff: 0.0]
[Ext Root Scanning (ms): Min: 0.4, Avg: 0.4, Max: 0.5, Diff: 0.1, Sum: 1.8]
[Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Processed Buffers: Min: 0, Avg: 2.8, Max: 11, Diff: 11, Sum: 11]
[Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Object Copy (ms): Min: 0.5, Avg: 0.5, Max: 0.5, Diff: 0.1, Sum: 2.0]
[Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
[GC Worker Total (ms): Min: 1.0, Avg: 1.0, Max: 1.0, Diff: 0.0, Sum: 3.9]
[GC Worker End (ms): Min: 923.7, Avg: 923.7, Max: 923.7, Diff: 0.0]
[Code Root Fixup: 0.0 ms]
[Code Root Migration: 0.0 ms]
[Clear CT: 0.0 ms]
[Other: 0.2 ms]
[Choose CSet: 0.0 ms]
[Ref Proc: 0.1 ms]
[Ref Enq: 0.0 ms]
[Free CSet: 0.0 ms]
[**Eden**: 14.0M(14.0M)->0.0B(20.0M) **Survivors**: 0.0B->1024.0K **Heap**: 14.0M(251.0M)->896.1K(251.0M)]
[Times: user=0.00 sys=0.00, real=0.00 secs]
>
>>A--- ----------
Heap
**garbage-first heap** total 257024K, used 896K [0x0000000700800000, 0x0000000710300000, 0x00000007fae00000)
**region size** 1024K, 2 young (2048K), 1 survivors (1024K)
**compacting perm gen** total 20480K, used 3164K [0x00000007fae00000, 0x00000007fc200000, 0x0000000800000000)
the space 20480K, 15% used [0x00000007fae00000, 0x00000007fb117388, 0x00000007fb117400, 0x00000007fc200000)
No shared spaces configured.
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