[jira] [Created] (FLINK-36227) NullPointerException when starting flink with logback logger

["Szymon (Jira)" <ji...@apache.org>]

Szymon created FLINK-36227:
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             Summary: NullPointerException when starting flink with logback logger
                 Key: FLINK-36227
                 URL: https://issues.apache.org/jira/browse/FLINK-36227
             Project: Flink
          Issue Type: Bug
          Components: API / Core
    Affects Versions: 1.20.0
         Environment: The error rise when flink is staring with  logback as logger
            Reporter: Szymon


I think that there is a bug in flink code in class MdcUtils.

 

When I run job on standalone flink or unit test with MiniCluster I get     below error. This error rise only when logback  is used, as logging adapter. I use logback version 1.2.13 because in flink documentation [https://nightlies.apache.org/flink/flink-docs-release-1.20/docs/deployment/advanced/logging/] is written “Logback 1.3+ requires SLF4J 2, which is currently not supported.”

 

_14:33:41.111 [flink-pekko.actor.default-dispatcher-5] INFO org.apache.flink.runtime.rpc.pekko.PekkoRpcActor - The RpcEndpoint taskmanager_0 failed._

_java.lang.NullPointerException: null_

        _at java.base/java.util.HashMap.putMapEntries(HashMap.java:497)_

        _at java.base/java.util.HashMap.putAll(HashMap.java:781)_

        _at java.base/java.util.Collections$SynchronizedMap.putAll(Collections.java:2604)_

        _at ch.qos.logback.classic.util.LogbackMDCAdapter.setContextMap(LogbackMDCAdapter.java:197)_

        _at org.slf4j.MDC.setContextMap(MDC.java:264)_

        _at org.apache.flink.util.MdcUtils.lambda$withContext$0(MdcUtils.java:48)_

 

I checked flink code and in my opinion there should be additional check in class MdcUtils in method

_public static MdcCloseable withContext(Map<String, String> context) {_
    _final Map<String, String> orig = MDC.getCopyOfContextMap();_
    _MDC.setContextMap(context);_
    _return () -> MDC.setContextMap(orig);_
_}_

 

this method use MDC.getCopyOfContextMap();. Description of this method says that returned value may be null. So when  variable orig is null and is passed to “MDC.setContextMap”. At the end this null is passed to class LogbackMDCAdapter to method setContextMap where this null Is passed to  newMap.putAll(contextMap), and then NullPointerException rise. I checked this for logback 1.2.13 where setContextMap is

_public void setContextMap(Map<String, String> contextMap) {_
    _lastOperation.set(WRITE_OPERATION);_

    _Map<String, String> newMap = Collections.synchronizedMap(new HashMap<String, String>());_
    _newMap.putAll(contextMap);_

    _// the newMap replaces the old one for serialisation's sake_
    _copyOnThreadLocal.set(newMap);_
_}_

 

This error should not appear when logback version is 1.3.3 or higher

_@SuppressWarnings("unchecked")_
_public void setContextMap(Map contextMap) {_
    _if (contextMap != null) {_
        _readWriteThreadLocalMap.set(new HashMap<String, String>(contextMap));_
    _} else {_
        _readWriteThreadLocalMap.set(null);_
    _}_
    _nullifyReadOnlyThreadLocalMap();_
_}_

 

 



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