jihoonson opened a new issue #6020: Race in taskMaster when the overlord becomes the leader URL: https://github.com/apache/incubator-druid/issues/6020 `TaskMaster` has the interfaces to return the variables (`taskRunner`, `taskQueue`, etc) which are initialized only when the overlord becomes the leader. The code of the interfaces is like this: ```java public Optional<TaskRunner> getTaskRunner() { if (overlordLeaderSelector.isLeader()) { return Optional.of(taskRunner); } else { return Optional.absent(); } } ``` However, `taskRunner` is initialized in `DruidLeaderSelector.Listener.becomeLeader()` which is called after the overlord becomes the leader, and thus `Optional.of()` throws an NPE. The full stack trace is as follows: ``` java.lang.NullPointerException at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:213) ~[guava-16.0.1.jar:?] at com.google.common.base.Optional.of(Optional.java:85) ~[guava-16.0.1.jar:?] at io.druid.indexing.overlord.TaskMaster.getTaskRunner(TaskMaster.java:214) ~[druid-indexing-service-0.12.1-iap8.jar:0.12.1-iap8] at io.druid.indexing.overlord.http.OverlordResource.getWorkers(OverlordResource.java:810) ~[druid-indexing-service-0.12.1-iap8.jar:0.12.1-iap8] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_163] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_163] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_163] at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_163] at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60) ~[jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ResponseOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:205) ~[jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75) ~[jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302) ~[jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147) ~[jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108) ~[jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147) ~[jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84) ~[jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1542) ~[jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1473) [jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1419) [jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1409) [jersey-server-1.19.3.jar:1.19.3] at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:409) [jersey-servlet-1.19.3.jar:1.19.3] at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:558) [jersey-servlet-1.19.3.jar:1.19.3] at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:733) [jersey-servlet-1.19.3.jar:1.19.3] at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) [javax.servlet-api-3.1.0.jar:3.1.0] at com.google.inject.servlet.ServletDefinition.doServiceImpl(ServletDefinition.java:286) [guice-servlet-4.1.0.jar:?] at com.google.inject.servlet.ServletDefinition.doService(ServletDefinition.java:276) [guice-servlet-4.1.0.jar:?] at com.google.inject.servlet.ServletDefinition.service(ServletDefinition.java:181) [guice-servlet-4.1.0.jar:?] at com.google.inject.servlet.ManagedServletPipeline.service(ManagedServletPipeline.java:91) [guice-servlet-4.1.0.jar:?] at com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:85) [guice-servlet-4.1.0.jar:?] at com.google.inject.servlet.ManagedFilterPipeline.dispatch(ManagedFilterPipeline.java:120) [guice-servlet-4.1.0.jar:?] at com.google.inject.servlet.GuiceFilter.doFilter(GuiceFilter.java:135) [guice-servlet-4.1.0.jar:?] at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502] at io.druid.server.http.RedirectFilter.doFilter(RedirectFilter.java:72) [druid-server-0.12.1-iap8.jar:0.12.1-iap8] at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502] at io.druid.server.security.PreResponseAuthorizationCheckFilter.doFilter(PreResponseAuthorizationCheckFilter.java:84) [druid-server-0.12.1-iap8.jar:0.12.1-iap8] at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502] at io.druid.server.security.AllowOptionsResourceFilter.doFilter(AllowOptionsResourceFilter.java:76) [druid-server-0.12.1-iap8.jar:0.12.1-iap8] at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502] at io.imply.security.ImplyAuthenticator$ImplyAuthenticationFilter.doFilter(ImplyAuthenticator.java:149) [imply-druid-security-0.12.0.3.jar:?] at io.druid.server.security.AuthenticationWrappingFilter.doFilter(AuthenticationWrappingFilter.java:60) [druid-server-0.12.1-iap8.jar:0.12.1-iap8] at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502] at io.druid.security.basic.authentication.BasicHTTPAuthenticator$BasicHTTPAuthenticationFilter.doFilter(BasicHTTPAuthenticator.java:162) [druid-basic-security-0.12.1-iap8.jar:0.12.1-iap8] at io.druid.server.security.AuthenticationWrappingFilter.doFilter(AuthenticationWrappingFilter.java:60) [druid-server-0.12.1-iap8.jar:0.12.1-iap8] at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502] at io.druid.server.security.SecuritySanityCheckFilter.doFilter(SecuritySanityCheckFilter.java:86) [druid-server-0.12.1-iap8.jar:0.12.1-iap8] at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:582) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:224) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1180) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:512) [jetty-servlet-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1112) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.handler.gzip.GzipHandler.handle(GzipHandler.java:493) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.handler.HandlerList.handle(HandlerList.java:52) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:134) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.Server.handle(Server.java:534) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:320) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:251) [jetty-server-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:283) [jetty-io-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:108) [jetty-io-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.io.ssl.SslConnection.onFillable(SslConnection.java:240) [jetty-io-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:283) [jetty-io-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:108) [jetty-io-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:93) [jetty-io-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.executeProduceConsume(ExecuteProduceConsume.java:303) [jetty-util-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceConsume(ExecuteProduceConsume.java:148) [jetty-util-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:136) [jetty-util-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:671) [jetty-util-9.3.19.v20170502.jar:9.3.19.v20170502] at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:589) [jetty-util-9.3.19.v20170502.jar:9.3.19.v20170502] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_163] ```
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