触发Full gc条件
本文参考:http://blog.csdn.net/chenleixing/article/details/46706039
给出各个场景下可能触发full gc的实例代码.
１．调用System.gc
import java.util.ArrayList;
import java.util.List;
/**
*
* created by: [email protected]
* created:2016年3月20日
*/
/**
* -XX:+UseSerialGC -Xms200M -Xmx200M -Xmn32m -XX:SurvivorRatio=8 -XX:+PrintGCDetails
* @author gxl
*
*/
public class SimulateFullGc
{
public static void main(String[] args)
{
//模拟fullgc场景
//场景1 使用System.gc
List[Full GC (System) [Tenured: 0K->1495K(172032K), 0.0048354 secs] 2073K->1495K(201536K), [Perm : 2529K->2529K(21248K)], 0.0048900 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System) [Tenured: 1495K->11735K(172032K), 0.0064495 secs] 13310K->11735K(201536K), [Perm : 2532K->2532K(21248K)], 0.0064752 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
由System.gc调用的ｇｃ标记Full GC (System).
2.老年代空间不足
/**
*
* created by: [email protected]
* created:2016年3月20日
*/
/**
* -XX:+UseSerialGC -Xms200M -Xmx200M -Xmn32m -XX:SurvivorRatio=8 -XX:+PrintGCDetails
* @author gxl
*
*/
public class SimulateFullGc
{
public static void main(String[] args)
{
//模拟fullgc场景
//老年代空间不足
//按照上面的参数推算:老年代大小: 200 -32m = 168M
byte [] MAXOBJ = new byte [1024 * 1024 * 100]; // 100M
byte [] MAXOBJ2 = new byte [1024 * 1024 * 70]; // 60M
MAXOBJ = null;
byte [] MAXOBJ3 = new byte [1024 * 1024 * 100]; // 60M
}
}
[GC [DefNew: 5145K->470K(29504K), 0.0029970 secs][Tenured: 106496K->106966K(172032K), 0.0027630 secs] 107545K->106966K(201536K), [Perm : 2528K->2528K(21248K)], 0.0057990 secs] [Times: user=0.00 sys=0.02, real=0.01 secs]
[Full GC [Tenured: 106966K->106952K(172032K), 0.0024331 secs] 106966K->106952K(201536K), [Perm : 2528K->2527K(21248K)], 0.0024488 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Exception in thread “main” java.lang.OutOfMemoryError: Java heap space
at SimulateFullGc.main(SimulateFullGc.java:27)
[GC [DefNew: 5145K->470K(29504K), 0.0029970 secs][Tenured: 106496K->106966K(172032K), 0.0027630 secs] 107545K->106966K(201536K), [Perm : 2528K->2528K(21248K)], 0.0057990 secs] [Times: user=0.00 sys=0.02, real=0.01 secs]
[Full GC [Tenured: 106966K->106952K(172032K), 0.0024331 secs] 106966K->106952K(201536K), [Perm : 2528K->2527K(21248K)], 0.0024488 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Exception in thread “main” java.lang.OutOfMemoryError: Java heap space
at SimulateFullGc.main(SimulateFullGc.java:27)
3.永久代空间不足
方式 在jdk6 上:
import java.util.ArrayList;
import java.util.List;
/**
*
* created by: [email protected]
* created:2016年3月20日
*/
/**
* -XX:+UseSerialGC -Xms200M -Xmx200M -Xmn32m -XX:SurvivorRatio=8 -XX:+PrintGCDetails -XX:MaxPermSize=10M
* @author gxl
*
*/
public class SimulateFullGc
{
public static void main(String[] args)
{
//模拟fullgc场景
//持久代空间不足
List list = new ArrayList();
int i = 0;
while (true)
{
list.add(String.valueOf("ABCD:" + i ++).intern());
}
}
}
[GC [DefNew: 26240K->937K(29504K), 0.0040883 secs] 26240K->937K(201536K), 0.0041121 secs] [Times: user=0.02 sys=0.00, real=0.01 secs]
[Full GC [Tenured: 0K->1325K(172032K), 0.0362063 secs] 17898K->1325K(201536K), [Perm : 20479K->20479K(20480K)], 0.0362549 secs] [Times: user=0.03 sys=0.00, real=0.04 secs]
[Full GC [Tenured: 1325K->1325K(172032K), 0.0326822 secs] 1325K->1325K(201536K), [Perm : 20479K->20479K(20480K)], 0.0327085 secs] [Times: user=0.03 sys=0.00, real=0.03 secs]
[Full GC [Tenured: 1325K->1325K(172032K), 0.0128924 secs] 1821K->1325K(201536K), [Perm : 20479K->3734K(20480K)], 0.0129210 secs] [Times: user=0.02 sys=0.00, real=0.01 secs]
Exception in thread “main” java.lang.OutOfMemoryError: PermGen space
at java.lang.String.intern(Native Method)
at SimulateFullGc.main(SimulateFullGc.java:25)
String.intern 会拷贝实例到永久代中.
在jdk1.7 不会,所以可以加载class来模拟:
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
/**
*
* created by: [email protected]
* created:2016年3月20日
*/
/**
* -XX:+UseSerialGC -Xms200M -Xmx200M -Xmn32m -XX:SurvivorRatio=8 -XX:+PrintGCDetails -XX:MaxPermSize=10M
* @author gxl
*
*/
public class SimulateFullGc
{
public static void main(String[] args)
{
//模拟fullgc场景
//持久代空间不足
//class 加载信息
//需要cglib + asm (http://forge.ow2.org/projects/asm/)
while (true)
{
Enhancer en = new Enhancer();
en.setSuperclass(OOMObject.class);
en.setUseCache(false);
en.setCallback(new MethodInterceptor()
{
@Override
public Object intercept(Object arg0, Method arg1, Object[] arg2,
MethodProxy arg3) throws Throwable
{
// TODO Auto-generated method stub
return null;
}
});
en.create();
}
}
static class OOMObject
{
}
}
[GC [DefNew: 26240K->1611K(29504K), 0.0039283 secs] 26240K->1611K(201536K), 0.0039524 secs] [Times: user=0.03 sys=0.00, real=0.00 secs]
…
[GC [DefNew: 28043K->1735K(29504K), 0.0039443 secs] 33739K->7817K(201536K), 0.0039660 secs] [Times: user=0.03 sys=0.00, real=0.00 secs]
[Full GC [Tenured: 6082K->7989K(172032K), 0.0322856 secs] 23097K->7989K(201536K), [Perm : 20479K->20479K(20480K)], 0.0323121 secs] [Times: user=0.05 sys=0.00, real=0.03 secs]
[Full GC [Tenured: 7989K->7989K(172032K), 0.0233015 secs] 7989K->7989K(201536K), [Perm : 20479K->20479K(20480K)], 0.0233266 secs] [Times: user=0.01 sys=0.00, real=0.02 secs]
[Full GC [Tenured: 7989K->7989K(172032K), 0.0199921 secs] 8515K->7989K(201536K), [Perm : 20479K->20479K(20480K)], 0.0200187 secs] [Times: user=0.03 sys=0.00, real=0.02 secs]
[Full GC [Tenured: 7989K->3354K(172032K), 0.0250219 secs] 7989K->3354K(201536K), [Perm : 20479K->20477K(20480K)], 0.0250530 secs] [Times: user=0.02 sys=0.00, real=0.03 secs]
Exception in thread “main” [Full GC [Tenured: 3354K->3355K(172032K), 0.0198650 secs] 3880K->3355K(201536K), [Perm : 20479K->20479K(20480K)], 0.0198919 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
[Full GC [Tenured: 3355K->3355K(172032K), 0.0198493 secs] 3355K->3355K(201536K), [Perm : 20479K->20479K(20480K)], 0.0198762 secs] [Times: user=0.03 sys=0.00, real=0.02 secs]
[Full GC [Tenured: 3355K->3355K(172032K), 0.0197512 secs] 3880K->3355K(201536K), [Perm : 20479K->20479K(20480K)], 0.0197814 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
[Full GC [Tenured: 3355K->3285K(172032K), 0.0245018 secs] 3355K->3285K(201536K), [Perm : 20479K->20478K(20480K)], 0.0245283 secs] [Times: user=0.03 sys=0.00, real=0.02 secs]
cglib & asm jar download:http://download.csdn.net/detail/u010926243/6721023
４． gc 担保失败
空间分配担保失败.
在发生MinorGC前,检查老年代是否有连续空间,如果有,则执行,如果没有,根据设置:-XX:-HandlePromotionFailure 指定,如果打开,那么继续检查,当前老年代最大可用连续空间大于平均历次晋升到老年代大小,如果大于,则进行MinorGC,否则进行FullGC,如果HandlePromotionFailure 不设置 直接进行FullGC.
大致就是这样:
代码:
该参数:-XX:-HandlePromotionFailure 在JDK 6U24中移除.后续判断只要剩余连续大于当前新生代或者历次晋升平均大小就会执行minorgc.
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option HandlePromotionFailure; support was removed in 6.0_24
搞了好久终于搞出来了:
import java.lang.reflect.Field;
import sun.misc.Unsafe;
/**
*
* created by: [email protected]
* created:2016年3月20日
*/
/**
* -Xms20M -Xmx20M -Xmn10m -XX:SurvivorRatio=8 -XX:+PrintGCDetails -XX:-HandlePromotionFailure -XX:MaxTenuringThreshold=1
* @author gxl
*
*/
public class SimulateFullGc
{
private static final int MB = 1024 * 1024;
public static void main(String[] args) throws Exception
{
// 模拟fullgc场景
// 提升担保
// 提升担保
byte[] M6, M3, M4, M5, M7, M8;
M6 = new byte[6 * MB];
M6[0] = 0;
M6[0] = 0;
// 使用2次保证下次需要的时候可以晋升到老年代 会晋升那么 晋升经验值为6M
M3 = new byte[4 * MB];
M4 = new byte[2 * MB];
M4 = null;
M5 = new byte[2 * MB];
M5[0] = 0;
M5[0] = 0;
M7 = new byte[2 * MB];
M7[0] = 0;
M7[0] = 0;
M7 = null;
M8 = new byte[3 * MB];
// 最终如下对象 老年代 M6 + M8 = 9M
// 年轻代:M3 + M5 = 6M = 6144K
System.out.println("M6 HEX:0x" + Long.toHexString(addressOf(M6)));
System.out.println("M5 HEX:0x" + Long.toHexString(addressOf(M5)));
System.out.println("M3 HEX:0x" + Long.toHexString(addressOf(M3)));
System.out.println("M8 HEX:0x" + Long.toHexString(addressOf(M8)));
}
private static Unsafe unsafe;
static
{
try
{
Field field = Unsafe.class.getDeclaredField("theUnsafe");
field.setAccessible(true);
unsafe = (Unsafe) field.get(null);
}
catch (Exception e)
{
e.printStackTrace();
}
}
public static long addressOf(Object o) throws Exception
{
Object[] array = new Object[] { o };
long baseOffset = unsafe.arrayBaseOffset(Object[].class);
int addressSize = unsafe.addressSize();
long objectAddress;
switch (addressSize)
{
case 4:
objectAddress = unsafe.getInt(array, baseOffset);
break;
case 8:
objectAddress = unsafe.getLong(array, baseOffset);
break;
default:
throw new Error("unsupported address size: " + addressSize);
}
return (objectAddress);
}
}
[GC [DefNew: 6487K->149K(9216K), 0.0027691 secs] 6487K->6293K(19456K), 0.0027839 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC [DefNew: 6379K->6379K(9216K), 0.0000060 secs][Tenured: 6144K->6144K(10240K), 0.0048112 secs] 12523K->10389K(19456K), [Perm : 374K->374K(12288K)], 0.0048426 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[Full GC [Tenured: 8192K->6144K(10240K), 0.0032886 secs] 14485K->12437K(19456K), [Perm : 374K->374K(12288K)], 0.0033058 secs] [Times: user=0.02 sys=0.00, real=0.00 secs]
M6 HEX:0x33990000
M5 HEX:0x333b5520
M3 HEX:0x32f90000
M8 HEX:0x33f90010
Heap
def new generation total 9216K, used 6514K [0x32f90000, 0x33990000, 0x33990000)
eden space 8192K, 79% used [0x32f90000, 0x335ec808, 0x33790000)
from space 1024K, 0% used [0x33890000, 0x33890000, 0x33990000)
to space 1024K, 0% used [0x33790000, 0x33790000, 0x33890000)
tenured generation total 10240K, used 9216K [0x33990000, 0x34390000, 0x34390000)
the space 10240K, 90% used [0x33990000, 0x34290020, 0x34290200, 0x34390000)
compacting perm gen total 12288K, used 374K [0x34390000, 0x34f90000, 0x38390000)
the space 12288K, 3% used [0x34390000, 0x343ed960, 0x343eda00, 0x34f90000)
ro space 10240K, 54% used [0x38390000, 0x3890c510, 0x3890c600, 0x38d90000)
rw space 12288K, 55% used [0x38d90000, 0x3942fb78, 0x3942fc00, 0x39990000)
注意对象位置.
5. Cocurrent mode failure
发生在cms的清理sweep阶段,发现有新的垃圾产生,而且老年代没有足够空间导致的.
关于cms:
初始标记(STW) - >并发标记 －＞重新标记（STW） －＞并发清除．
STW = stop the world.
Ref:
get the object memory address
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