The problem described below has occured two times in our product enviroment

[runfriends]

the problem has occured two times, however the program could resume after restarting.

• [ X ] I have searched the issues of this repository and believe that this is not a duplicate.
• [ X ] I have checked the FAQ of this repository and believe that this is not a duplicate.

Environment

• Dubbo version: 2.6.0
• Operating System version: CentOS 6.9 kernel 2.6.32
• Java version: 1.8.0_51-b16

HEAP DUMP ANALYSIS

The classloader/component "sun.misc.Launcher$AppClassLoader @ 0xc00009e0" occupies 218,169,664 (20.50%) bytes. The memory is accumulated in one instance of "java.lang.Object[]" loaded by "".

Class Name	Shallow Heap	Retained Heap
java.util.concurrent.ConcurrentHashMap$Node[65536] @ 0xef72bd20	262,160	206,175,368
table java.util.concurrent.ConcurrentHashMap @ 0xc1caa0f0	64	206,175,432
notified com.alibaba.dubbo.registry.zookeeper.ZookeeperRegistry @ 0xc0e90f00	104	287,488,568
this$0 com.alibaba.dubbo.registry.support.FailbackRegistry$1 @ 0xc0e91130	16	16
task java.util.concurrent.Executors$RunnableAdapter @ 0xc0e91118	24	40
java.lang.Thread @ 0xc0737418 DubboRegistryFailedRetryTimer-thread-1 Thread	120	472
callable java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask @ 0xc0e910d0 »	72	72
Total: 2 entries
registry com.alibaba.dubbo.registry.integration.RegistryDirectory @ 0xc1961620 »	80	3,328
val$registry com.alibaba.dubbo.registry.integration.RegistryProtocol$1 @ 0xc1498860 »	40	40
val$registry com.alibaba.dubbo.registry.integration.RegistryProtocol$1 @ 0xc165e460 »	40	40
val$registry com.alibaba.dubbo.registry.integration.RegistryProtocol$1 @ 0xc1d449b8 »	40	40
val$registry com.alibaba.dubbo.registry.integration.RegistryProtocol$1 @ 0xc25720b8 »	40	40
Total: 6 entries

SOME THREAD STACK

com.alibaba.dubbo.rpc.RpcException: No provider available from registry 172.16.0.128:2181 for service **SERVICE NAME HERE** on consumer 172.16.0.128 use dubbo version 2.6.0, may be providers disabled or not registered ?
	at com.alibaba.dubbo.registry.integration.RegistryDirectory.doList(RegistryDirectory.java:572) ~[dubbo-2.6.0.jar:2.6.0]
	at com.alibaba.dubbo.rpc.cluster.directory.AbstractDirectory.list(AbstractDirectory.java:73) ~[dubbo-2.6.0.jar:2.6.0]
	at com.alibaba.dubbo.rpc.cluster.support.AbstractClusterInvoker.list(AbstractClusterInvoker.java:265) ~[dubbo-2.6.0.jar:2.6.0]
	at com.alibaba.dubbo.rpc.cluster.support.AbstractClusterInvoker.invoke(AbstractClusterInvoker.java:224) ~[dubbo-2.6.0.jar:2.6.0]
	at com.alibaba.dubbo.rpc.cluster.support.wrapper.MockClusterInvoker.invoke(MockClusterInvoker.java:70) ~[dubbo-2.6.0.jar:2.6.0]
	at com.alibaba.dubbo.rpc.proxy.InvokerInvocationHandler.invoke(InvokerInvocationHandler.java:51) ~[dubbo-2.6.0.jar:2.6.0]
	at com.alibaba.dubbo.common.bytecode.proxy7.queryId(proxy7.java) ~[dubbo-2.6.0.jar:2.6.0]

[Geker]

No provider 的情况下，ReferenceConfig创建失败，但是destory()时，dubbo没有清理已经注册到AbstractRegistry的属性notified的URL。导致内存泄漏。
private final ConcurrentMap<URL, Map<String, List>> notified = new ConcurrentHashMap<>();
可以失败时，反射主动进行清理。