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按照java内存的结构,发生内存溢出的地方常在于堆、栈、方法区、直接内存。
一、堆溢出
堆溢出原因莫过于对象太多导致,看代码:
/** * java 堆溢出 * VM Args:-Xms20m -Xmx20m -XX:+HeapDumpOnOutOfMemoryError * @author */ public class HeapOOM { static class OOMObject { } public static void main(String[] args) { List<OOMObject> list = new ArrayList<OOMObject>(); while (true) { list.add(new OOMObject()); /*System.out.println("total(k):"+Runtime.getRuntime().totalMemory()/1024+ " freeMemory(k):"+Runtime.getRuntime().freeMemory()/1024+ " maxMemory(k):"+Runtime.getRuntime().maxMemory()/1024+ " availableProcessors:"+Runtime.getRuntime().availableProcessors());*/ } } } /** * java.lang.OutOfMemoryError: Java heap space Dumping heap to java_pid1820.hprof ... Heap dump file created [24787111 bytes in 0.346 secs] Exception in thread "main" java.lang.OutOfMemoryError: Java heap space at java.util.Arrays.copyOf(Arrays.java:2760) at java.util.Arrays.copyOf(Arrays.java:2734) at java.util.ArrayList.ensureCapacity(ArrayList.java:167) at java.util.ArrayList.add(ArrayList.java:351) at baby.oom.HeapOOM.main(HeapOOM.java:19) * * */
二、栈溢出
根据JAVA虚拟机规范描述:如果线程请求的栈深度大于虚拟机所允许的最大深度,将抛出StackOverflowError
如果虚拟机在扩展栈时无法申请到足够的内存空间,将抛出OutOfMemoryError。
实验表明:在单线程下,无论是由于栈帧太大还是虚拟机栈容量太小,当内存无法分配的时候,虚拟机抛出的都是StackOverflowError。
通过不断的建立新线程的方式可以产生内存溢出溢出。为每个线程的栈分配的内存越大,反而越容易产生内存溢出异常。如果是建立过多线程导致的内存溢出,在不能减少线程数量或者更换64位虚拟机的情况下,就只能通过减少最大堆和减少栈容量来换取更多的线程。
假设32位windows系统虚拟机最大设为2G,虚拟机提供了参数来控制java堆和方法区这两部分最大值,剩余的内存为2G - Xmx- MaxPermSize,如果虚拟机本身进程内存大小不算在内,省下的内存就有虚拟机和本地方法栈瓜分了。每个线程分配到的栈容量越大,可以建立的线程数量自然就越少。
/** * 栈异常 * 如果线程请求的栈深度大于虚拟机所允许的最大深度,将抛出StackOverflowError * 如果虚拟机在扩展栈时无法申请到足够的内存空间,将抛出OutOfMemoryError * VM Args:-Xss128k * @author */ public class JavaVMStackSOF { private int stackLength = 1; public void stackLeak() { stackLength++; stackLeak(); } public static void main(String[] args) throws Throwable { JavaVMStackSOF oom = new JavaVMStackSOF(); try { oom.stackLeak(); } catch (Throwable e) { System.out.println("stack length:" + oom.stackLength); throw e; } } } /** * * stack length:2403 Exception in thread "main" java.lang.StackOverflowError at baby.oom.JavaVMStackSOF.stackLeak(JavaVMStackSOF.java:11) at baby.oom.JavaVMStackSOF.stackLeak(JavaVMStackSOF.java:12) at baby.oom.JavaVMStackSOF.stackLeak(JavaVMStackSOF.java:12) 默认情况下,即不加Xss限制,输出的length为8956,加了Xss128k length位2403 */
/** * VM Args:-Xss2M (这时候不妨设大些) * @author */ public class JavaVMStackOOM { int i=0; private void dontStop() { while (true) { } } public void stackLeakByThread() { while (true) { Thread thread = new Thread(new Runnable() { @Override public void run() { dontStop(); } }); i++; System.out.println("i="+i); thread.start(); } } public static void main(String[] args) throws Throwable { JavaVMStackOOM oom = new JavaVMStackOOM(); try { oom.stackLeakByThread(); } catch (Throwable e) { System.out.println("thread num:" + oom.i); throw e; } } } //i=391 //thread num:391 //Exception in thread "main" java.lang.OutOfMemoryError: unable to create new native thread
三、方法区溢出
当运行时常量池过大或者类过多时就会导致方法区溢出。
import java.util.ArrayList; import java.util.List; /** * VM Args:-XX:PermSize=10M -XX:MaxPermSize=10M * @author */ public class RuntimeConstantPoolOOM { public static void main(String[] args) { // 使用List保持着常量池引用,避免Full GC回收常量池行为 List<String> list = new ArrayList<String>(); // 10MB的PermSize在integer范围内足够产生OOM了 int i = 0; while (true) { list.add(String.valueOf(i++).intern()); } } } /** Exception in thread "main" java.lang.OutOfMemoryError: PermGen space at java.lang.String.intern(Native Method) at baby.oom.RuntimeConstantPoolOOM.main(RuntimeConstantPoolOOM.java:18) */ /** * VM Args: -XX:PermSize=10M -XX:MaxPermSize=10M * @author */ public class JavaMethodAreaOOM { public static void main(String[] args) { while (true) { Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(OOMObject.class); enhancer.setUseCache(false); enhancer.setCallback(new MethodInterceptor() { @Override public Object intercept(Object obj, Method method, Object[] arg, MethodProxy proxy) throws Throwable { // TODO Auto-generated method stub return proxy.invokeSuper(obj, arg); } }); enhancer.create(); } } static class OOMObject { } } /* * Exception in thread "main" net.sf.cglib.core.CodeGenerationException: java.lang.reflect.InvocationTargetException-->null at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:237) at net.sf.cglib.proxy.Enhancer.createHelper(Enhancer.java:377) at net.sf.cglib.proxy.Enhancer.create(Enhancer.java:285) at baby.oom.JavaMethodAreaOOM.main(JavaMethodAreaOOM.java:28) Caused by: java.lang.reflect.InvocationTargetException at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at net.sf.cglib.core.ReflectUtils.defineClass(ReflectUtils.java:384) at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:219) ... 3 more Caused by: java.lang.OutOfMemoryError: PermGen space at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631) at java.lang.ClassLoader.defineClass(ClassLoader.java:615) ... 8 more */
四、直接内存溢出
虽然使用DerictByteBuffer分配内存也会抛出内存溢出异常,但它抛出异常时并没有真正向操作系统申请分配,而是通过计算得知内存无法分配,于是手动抛出异常,真正申请分配内存的方法是unsafe.allocateMemory()。
import java.lang.reflect.Field; import sun.misc.Unsafe; /** * VM Args:-Xmx20M -XX:MaxDirectMemorySize=10M * @author * Eclipse 默认把这些受访问限制的API设成了ERROR。 解决办法:将Windows->Preferences->Java-Complicer->Errors/Warnings->Deprecated and restricted API,中的Forbidden references(access rules)设置为Warning,即可以编译通过。 */ public class DirectMemoryOOM { private static final int _1MB = 1024 * 1024; public static void main(String[] args) throws Exception { Field unsafeField = Unsafe.class.getDeclaredFields()[0]; unsafeField.setAccessible(true); Unsafe unsafe = (Unsafe) unsafeField.get(null); while (true) { unsafe.allocateMemory(_1MB); } } } /** Exception in thread "main" java.lang.OutOfMemoryError at sun.misc.Unsafe.allocateMemory(Native Method) at baby.oom.DirectMemoryOOM.main(DirectMemoryOOM.java:20) */
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原文地址:http://www.cnblogs.com/moonandstar08/p/5401182.html