如何创建java.lang.OutOfMemoryError:元空间？

Question

我的目标是模拟一种我可以接收到这个错误的情况。我试过了How to simulate OutOfMemoryError: Metaspace，但是没有用。

我在config中设置：-XX:MaxMetaspaceSize=50m

已经尝试过了：

public class Main {
    public static void main(String[] args) {
        for (int i = 0; ; i++) {
            Thread thread = new Thread(new A());
            thread.start();
        }
    }
}

和它:A和B POJO类

public class Main {
    static Map<A,B> map = new LinkedHashMap<>();
    public static void main(String[] args) {
        while (true){
            A a = new A();
            B b = new B();
           map.put(a,b);
        }
    }
}

Answer 1

正如您提到的，您希望抛出一个java.lang.OutOfMemoryError: Metaspace。为了实现这一点，你必须加载很多不同的类。这可以通过利用javaassist来实现

   static javassist.ClassPool cp = javassist.ClassPool.getDefault();

    public static void main(String[] args) throws Exception{
        for (int i = 0; ; i++) {
            Class c = cp.makeClass("mypackage.Myclass" + i).toClass();
        }
    }

具有以下元空间设置：

-XX:MaxMetaspaceSize=10m
-XX:MetaspaceSize=2M
-XX:MaxMetaspaceFreeRatio=1
-XX:MaxMetaspaceExpansion=1K
-XX:MinMetaspaceFreeRatio=1
-XX:InitialBootClassLoaderMetaspaceSize=2M

在没有javaassist的情况下，可以生成保持相同元空间选项的java.lang.OutOfMemoryEror: Metaspace，如下所示：

            String clazzBase64 = "yv66vgAAADcADAEAEm15cGFja2FnZS9NeWNsYXNzMAcAAQEAEGphdmEvbGFuZy9PYmplY3QHAAMBAApTb3VyY2VGaWxlAQANTXljbGFzczAuamF2YQEABjxpbml0PgEAAygpVgwABwAICgAEAAkBAARDb2RlACEAAgAEAAAAAAABAAEABwAIAAEACwAAABEAAQABAAAABSq3AAqxAAAAAAABAAUAAAACAAY=";
            byte[] compiledClazz = Base64.getDecoder().decode(clazzBase64);
            int len = Integer.valueOf(compiledClazz[12]);

            MyClassLoader myClassLoader = new MyClassLoader(Thread.currentThread().getContextClassLoader());

            for (int i = 0; ; i++) {
                byte[] bytes = String.valueOf(i).getBytes();
                byte[] bytecode = new byte[compiledClazz.length + bytes.length - 1];
                System.arraycopy(compiledClazz, 0, bytecode, 0, 30);
                bytecode[12] = (byte)( len + bytes.length - 1 & 0xFF);

                System.arraycopy(bytes, 0, bytecode, 30, bytes.length);
                System.arraycopy(compiledClazz, 31, bytecode, 30 + bytes.length, compiledClazz.length - 31);

                String classname ="mypackage.Myclass" + i;
                Class c = myClassLoader.getClass(classname, bytecode);
            }

            public static class MyClassLoader extends ClassLoader {
               public MyClassLoader(ClassLoader parent) {
                  super(parent);
               }

               public Class<?> getClass(String name, byte[] code) {
                  return defineClass(name, code, 0, code.length);
               }
            }