JVM之JVM内存溢出

JVM内存溢出

Java内存区域分为程序计数器，方法区，堆区，虚拟机栈和本地方法栈。

其中程序计数器，虚拟机栈和本地方法栈是线程私有的；堆区和方法区是线程共享的。

而在HotSpot虚拟机中是直接将虚拟机栈和本地方法栈合到一起。

程序计数器。此区域没有定义任何OutOfMemory异常。

堆区。

设置堆区大小20M，不可扩展；通过list保持对象到GC Roots可达。

-Xms20M -Xmx20M -XX:+HeapDumpOnOutOfMemoryError

public class HeapTestMain {
    static class OOMObject {}
    public static void main(String[] args) {
        List<OOMObject> list = new ArrayList();
        while(true ) {
            list.add(new OOMObject());
        }
    }

}

java.lang.OutOfMemoryError: Java heap space
Dumping heap to java_pid23352.hprof ...
Heap dump file created [28245988 bytes in 0.065 secs]
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at java.util.Arrays.copyOf(Arrays.java:3210)
	at java.util.Arrays.copyOf(Arrays.java:3181)
	at java.util.ArrayList.grow(ArrayList.java:265)
	at java.util.ArrayList.ensureExplicitCapacity(ArrayList.java:239)
	at java.util.ArrayList.ensureCapacityInternal(ArrayList.java:231)
	at java.util.ArrayList.add(ArrayList.java:462)
	at oomtest.HeapTestMain.main(HeapTestMain.java:15)

虚拟机栈

设置栈大小128K -Xss128K

单一线程环境下，循环递归，增加栈长度。

public class StackTestMain {

    static class StackOOMObject{
        private int len = 0;
        public void stackLeak() {
            len++;
            stackLeak();
        }
    }

    public static void main(String[] args) {
        StackOOMObject obj = new StackOOMObject();
        try {
            obj.stackLeak();
        } catch (Error e) {
            System.out.println(obj.len);
            throw e;
        }
    }

}

996
Exception in thread "main" java.lang.StackOverflowError
	at oomtest.StackTestMain$StackOOMObject.stackLeak(StackTestMain.java:11)
	at oomtest.StackTestMain$StackOOMObject.stackLeak(StackTestMain.java:12)
	at oomtest.StackTestMain$StackOOMObject.stackLeak(StackTestMain.java:12)
	at 
	...
oomtest.StackTestMain$StackOOMObject.stackLeak(StackTestMain.java:12)
	at oomtest.StackTestMain.main(StackTestMain.java:19)

Process finished with exit code 1

方法区

(1) 运行时常量池

版本差异：

JDK1.6之前，方法区包括运行时常量池在永久代中；

JDK1.7，方法区和运行时常量池在永久代，字符串常量池在堆中；

JDK1.8，永久代被废弃，方法区在元空间，运行时常量池和字符串常量池在堆中。

程序：

public class MethodAreaTestMain {
    public static void main(String[] args) {
        List<String> list = new ArrayList();
        String str = "";
        while(true) {
            for(int i=0;i<10;i++) {
                list.add((str+i).intern());
            }
            list.add((str=str+"0").intern());
        }
    }
}

设置永久代10M，不可扩展 -XX:PermSize=10M -XX:MaxPermSize=10M

jdk1.6运行结果：

Exception in thread "main" java.lang.OutOfMemoryError: PermGen space
	at java.lang.String.intern(Native Method)
	at oomtest.MethodAreaTestMain.main(MethodAreaTestMain.java from InputFileObject:15)

jdk1.7运行结果：

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at oomtest.MethodAreaTestMain.main(MethodAreaTestMain.java:15)

jdk1.8运行结果：

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at oomtest.MethodAreaTestMain.main(MethodAreaTestMain.java:15)
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option PermSize=10M; support was removed in 8.0
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=10M; support was removed in 8.0

设置堆区10M，不可扩展 -Xms10M -Xmx10M

jdk1.8运行结果：

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at java.util.Arrays.copyOf(Arrays.java:3210)
	at java.util.Arrays.copyOf(Arrays.java:3181)
	at java.util.ArrayList.grow(ArrayList.java:265)
	at java.util.ArrayList.ensureExplicitCapacity(ArrayList.java:239)
	at java.util.ArrayList.ensureCapacityInternal(ArrayList.java:231)
	at java.util.ArrayList.add(ArrayList.java:462)
	at oomtest.MethodAreaTestMain.main(MethodAreaTestMain.java:15)

jdk1.7执行结果：

Exception in thread "main" java.lang.OutOfMemoryError: GC overhead limit exceeded
	at java.util.Arrays.copyOf(Arrays.java:2367)
	at java.lang.AbstractStringBuilder.expandCapacity(AbstractStringBuilder.java:130)
	at java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:114)
	at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:415)
	at java.lang.StringBuilder.append(StringBuilder.java:132)
	at oomtest.MethodAreaTestMain.main(MethodAreaTestMain.java:15)

jdk1.6运行结果：

Exception in thread "main" java.lang.OutOfMemoryError: PermGen space
	at java.lang.String.intern(Native Method)
	at oomtest.MethodAreaTestMain.main(MethodAreaTestMain.java from InputFileObject:15)

(2) 方法区

通过cglib，动态生成大量代理类。

public class MethodAreaTestMain {
    static class MethodAreaOOMObject {}
    public static void main(String[] args) {
        while(true) {
            Enhancer enhancer = new Enhancer();
            enhancer.setSuperclass(MethodAreaOOMObject.class);
            enhancer.setUseCache(false);
            enhancer.setCallback(new MethodInterceptor() {
                public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
                    return methodProxy.invokeSuper(o, objects);
                }
            });
            enhancer.create();
        }
    }
}

设置永久代10M -XX:PermSize=10M -XX:MaxPermSize=10M

jdk1.6结果：

Exception in thread "main" net.sf.cglib.core.CodeGenerationException: java.lang.reflect.InvocationTargetException-->null
	at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:256)
	at net.sf.cglib.proxy.Enhancer.createHelper(Enhancer.java:378)
	at net.sf.cglib.proxy.Enhancer.create(Enhancer.java:286)
	at oomtest.MethodAreaTestMain.main(MethodAreaTestMain.java from InputFileObject:24)
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:395)
	at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:237)
	... 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

jdk1.7结果：

Exception in thread "main" 
Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "main"

设置元空间10M jdk1.8结果：

Exception in thread "main" net.sf.cglib.core.CodeGenerationException: java.lang.reflect.InvocationTargetException-->null
	at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:256)
	at net.sf.cglib.proxy.Enhancer.createHelper(Enhancer.java:378)
	at net.sf.cglib.proxy.Enhancer.create(Enhancer.java:286)
	at oomtest.MethodAreaTestMain.main(MethodAreaTestMain.java:27)
Caused by: java.lang.reflect.InvocationTargetException
	at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at net.sf.cglib.core.ReflectUtils.defineClass(ReflectUtils.java:395)
	at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:237)
	... 3 more
Caused by: java.lang.OutOfMemoryError: Metaspace
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
	... 8 more

直接内存溢出

通过反射获取sun.misc.Unsafe实例分配内存。

public class DirectMemoryTestMain {
    static int _1MB = 1024 * 1024;
    public static void main(String[] args) throws IllegalAccessException {
        Field field = Unsafe.class.getDeclaredFields()[0];
        field.setAccessible(true);
        Unsafe unsafe = (Unsafe)field.get(null);
        while(true) {
            unsafe.allocateMemory(_1MB);
        }
    }
}

结果：

Exception in thread "main" java.lang.OutOfMemoryError
	at sun.misc.Unsafe.allocateMemory(Native Method)
	at oomtest.DirectMemoryTestMain.main(DirectMemoryTestMain.java:17)

JVM之JVM内存溢出

JVM内存溢出

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