Hazelcast：LinkageError "attempted duplicate class definition for name"

Question

我在我们的 hazelcast 集群中看到了这个错误。

代码正在尝试调用 IMap 上的 executeOnKey()。例如

    IMap<MyKey, MyCachedClass> myMap = hz.getMap("my-map");
    myMap.executeOnKey(myKey, new EntryProcessor() {
        @Override
        public Object process(Map.Entry entry) {
            return entry.getValue().setItem(item);
        }

        @Override
        public EntryBackupProcessor getBackupProcessor() {
            return null;
        }
    });

...我收到此异常：

Exception in thread "MYTHREAD" java.lang.LinkageError: loader (instance of com/hazelcast/internal/usercodedeployment/impl/ClassSource): attempted duplicate class definition for name: "com/mycompany/model/Item$ItemEnum"
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.lang.ClassLoader.defineClass(ClassLoader.java:642)
at com.hazelcast.internal.usercodedeployment.impl.ClassSource.define(ClassSource.java:50)
at com.hazelcast.internal.usercodedeployment.impl.ClassLocator.tryToGetClassFromRemote(ClassLocator.java:163)
at com.hazelcast.internal.usercodedeployment.impl.ClassLocator.handleClassNotFoundException(ClassLocator.java:95)
at com.hazelcast.internal.usercodedeployment.impl.ClassSource.loadClass(ClassSource.java:65)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.lang.ClassLoader.defineClass(ClassLoader.java:642)
at com.hazelcast.internal.usercodedeployment.impl.ClassSource.define(ClassSource.java:50)
at com.hazelcast.internal.usercodedeployment.impl.ClassLocator.tryToGetClassFromRemote(ClassLocator.java:161)
at com.hazelcast.internal.usercodedeployment.impl.ClassLocator.handleClassNotFoundException(ClassLocator.java:95)
at com.hazelcast.internal.usercodedeployment.UserCodeDeploymentService.handleClassNotFoundException(UserCodeDeploymentService.java:89)
at com.hazelcast.internal.usercodedeployment.UserCodeDeploymentClassLoader.loadClass(UserCodeDeploymentClassLoader.java:57)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at com.hazelcast.nio.ClassLoaderUtil.tryLoadClass(ClassLoaderUtil.java:288)
at com.hazelcast.nio.ClassLoaderUtil.loadClass(ClassLoaderUtil.java:237)
at com.hazelcast.nio.IOUtil$ClassLoaderAwareObjectInputStream.resolveClass(IOUtil.java:646)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1868)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1751)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2042)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:431)
at java.util.ArrayList.readObject(ArrayList.java:797)
at sun.reflect.GeneratedMethodAccessor18.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:1170)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2178)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2069)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2287)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2211)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2069)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2287)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2211)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2069)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2287)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2211)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2069)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:431)
at com.hazelcast.internal.serialization.impl.JavaDefaultSerializers$JavaSerializer.read(JavaDefaultSerializers.java:82)
at com.hazelcast.internal.serialization.impl.JavaDefaultSerializers$JavaSerializer.read(JavaDefaultSerializers.java:75)
at com.hazelcast.internal.serialization.impl.StreamSerializerAdapter.read(StreamSerializerAdapter.java:48)
at com.hazelcast.internal.serialization.impl.AbstractSerializationService.readObject(AbstractSerializationService.java:269)
at com.hazelcast.internal.serialization.impl.ByteArrayObjectDataInput.readObject(ByteArrayObjectDataInput.java:574)
at com.hazelcast.map.impl.operation.EntryOperation.readInternal(EntryOperation.java:263)
at com.hazelcast.spi.Operation.readData(Operation.java:728)
at com.hazelcast.internal.serialization.impl.DataSerializableSerializer.readInternal(DataSerializableSerializer.java:160)
at com.hazelcast.internal.serialization.impl.DataSerializableSerializer.read(DataSerializableSerializer.java:106)
at com.hazelcast.internal.serialization.impl.DataSerializableSerializer.read(DataSerializableSerializer.java:51)
at com.hazelcast.internal.serialization.impl.StreamSerializerAdapter.read(StreamSerializerAdapter.java:48)
at com.hazelcast.internal.serialization.impl.AbstractSerializationService.toObject(AbstractSerializationService.java:187)
at com.hazelcast.spi.impl.NodeEngineImpl.toObject(NodeEngineImpl.java:323)
at com.hazelcast.spi.impl.operationservice.impl.OperationRunnerImpl.run(OperationRunnerImpl.java:398)
at com.hazelcast.spi.impl.operationexecutor.impl.OperationThread.process(OperationThread.java:153)
at com.hazelcast.spi.impl.operationexecutor.impl.OperationThread.process(OperationThread.java:123)
at com.hazelcast.spi.impl.operationexecutor.impl.OperationThread.run(OperationThread.java:110)
at ------ submitted from ------.(Unknown Source)
at com.hazelcast.spi.impl.operationservice.impl.InvocationFuture.resolve(InvocationFuture.java:127)
at com.hazelcast.spi.impl.operationservice.impl.InvocationFuture.resolveAndThrowIfException(InvocationFuture.java:79)
at com.hazelcast.spi.impl.AbstractInvocationFuture.get(AbstractInvocationFuture.java:162)
at com.hazelcast.map.impl.proxy.MapProxySupport.executeOnKeyInternal(MapProxySupport.java:1099)
at com.hazelcast.map.impl.proxy.MapProxyImpl.executeOnKeyInternal(MapProxyImpl.java:109)
at com.hazelcast.map.impl.proxy.MapProxyImpl.executeOnKey(MapProxyImpl.java:757)
at com.mycompany.Processor.java

所以对我来说这看起来像：

'executeOnKey(item)' 命令正在发送到 'other' 节点此数据所在的集群。
另一个节点正在尝试反序列化 'item'。
其他节点找不到内部枚举的 class 'Item$ItemEnum'
另一个节点向 UserCodeDeploymentService 发出请求以获取 class 定义。
获取 class 定义后，它会尝试创建新的 class，一个发生链接错误。

我只是不明白为什么它会收到重复的 class 异常，当它第一次声称找不到 class 时。这个错误被证明很难复制。

我们确实 'userCodeDeployment' 设置为允许加载远程 class 定义。我们的配置如下所示：

UserCodeDeploymentConfig ucdConfig = new UserCodeDeploymentConfig();
ucdConfig.setEnabled(true);
ucdConfig.setClassCacheMode(UserCodeDeploymentConfig.ClassCacheMode.ETERNAL);
ucdConfig.setProviderMode(UserCodeDeploymentConfig.ProviderMode.LOCAL_AND_CACHED_CLASSES);
config.setUserCodeDeploymentConfig(ucdConfig);

所以它看起来有点像我期望的那样。即获取远程 class 定义，因为它无法在本地找到它。只是关于为什么会发生异常的一个谜。

Answer 1

尝试将 EntryProcessor 创建为静态或顶级 class 并在其构造函数中显式传递 item。这有望解决问题。

JVM 在动态 class 加载时可能会有点棘手，这是由 UserCodeDeployment 完成的。

Answer 2

最终解决了这个问题。

一个简单的例子。

假设有两个 Hazelcast 节点。两者都打开了 userCodeDeployment。（能够通过网络共享 class 定义。）
节点 1 在其 class 路径上有 MyClass，节点 2 没有。
MyClass 定义，注意内部枚举（我认为内部枚举可以换成内部 class，同样的事情也会发生）。

public class MyClass implements Serializable {

    private final InnerEnum enumVal;

    public MyClass(InnerEnum enumVal) {
        this.enumVal = enumVal;
    }

    public enum InnerEnum {
        ONE, TWO, THREE;
    }
}

从节点1开始，下面的代码是运行：

hz.getMap("myClassMap").put("myClassKey", new MyClass(MyClass.InnerEnum.ONE));
hz.getMap("myInnerEnumMap").put("myInnerEnumKey", MyClass.InnerEnum.TWO);

那么，在节点2上，下面的代码是运行：

System.out.println(hz.getMap("myInnerEnumMap").get("myInnerEnumKey"));
System.out.println(hz.getMap("myClassMap").get("myClassKey"));

在节点 2 上，我看到记录了以下内容：

[TRACE] ClassLocator Loaded class com.mycompany.MyClass$InnerEnum from Member [myhost]:5701 - cc0b2872-7f5b-484b-a40f-7c7ba1fdc165
TWO
[TRACE] ClassLocator Loaded class com.mycompany.MyClass from Member [myhost]:5701 - cc0b2872-7f5b-484b-a40f-7c7ba1fdc165

Exception in thread "main" java.lang.LinkageError: loader (instance of  com/hazelcast/internal/usercodedeployment/impl/ClassSource): attempted  duplicate class definition for name: "com/mycompany/MyClass$InnerEnum"
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:642)
    at com.hazelcast.internal.usercodedeployment.impl.ClassSource.define(ClassSource.java:50)
    at com.hazelcast.internal.usercodedeployment.impl.ClassLocator.tryToGetClassFromRemote(ClassLocator.java:163)
    at com.hazelcast.internal.usercodedeployment.impl.ClassLocator.handleClassNotFoundException(ClassLocator.java:95)
    at com.hazelcast.internal.usercodedeployment.UserCodeDeploymentService.handleClassNotFoundException(UserCodeDeploymentService.java:89)
    at com.hazelcast.internal.usercodedeployment.UserCodeDeploymentClassLoader.loadClass(UserCodeDeploymentClassLoader.java:57)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at com.hazelcast.nio.ClassLoaderUtil.tryLoadClass(ClassLoaderUtil.java:288)
    at com.hazelcast.nio.ClassLoaderUtil.loadClass(ClassLoaderUtil.java:237)
    at com.hazelcast.nio.IOUtil$ClassLoaderAwareObjectInputStream.resolveClass(IOUtil.java:646)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1868)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1751)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2042)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1573)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:431)
    at com.hazelcast.internal.serialization.impl.JavaDefaultSerializers$JavaSerializer.read(JavaDefaultSerializers.java:82)
    at com.hazelcast.internal.serialization.impl.JavaDefaultSerializers$JavaSerializer.read(JavaDefaultSerializers.java:75)
    at com.hazelcast.internal.serialization.impl.StreamSerializerAdapter.read(StreamSerializerAdapter.java:48)
    at com.hazelcast.internal.serialization.impl.AbstractSerializationService.toObject(AbstractSerializationService.java:187)
    at com.hazelcast.map.impl.proxy.MapProxySupport.toObject(MapProxySupport.java:1245)
    at com.hazelcast.map.impl.proxy.MapProxyImpl.get(MapProxyImpl.java:120)
    at com.mycompany.main(Node2.java:74)

所以：

节点 2 首先尝试获取并显示 MyClass$InnerEnum 的实例。它通过 hazelcast 从节点 1 获取 InnerEnum class 定义。
然后节点 2 尝试获取并显示 MyClass 的实例。它从节点 1 获取 MyClass class 定义。
Hazelcast 然后循环遍历 MyClass 的内部 classes（它只包含 InnerEnum）并要求 class 加载器定义它们而不检查它们是否已经存在。

参见（来自 Hazelcast 3.11.1） com.hazelcast.internal.usercodedeployment.impl.ClassLocator:160

Map<String, byte[]> innerClassDefinitions = classData.getInnerClassDefinitions();
classSource.define(name, classData.getMainClassDefinition());
for (Map.Entry<String, byte[]> entry : innerClassDefinitions.entrySet()) {
    classSource.define(entry.getKey(), entry.getValue());
}

在我们的案例中，最简单的解决方案是将 InnerEnum 拉出作为顶级枚举。

Hazelcast：LinkageError "attempted duplicate class definition for name"

Hazelcast: LinkageError "attempted duplicate class definition for name"

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