Alexander Kudrevatykh created LOGBACK-1362: ---------------------------------------------- Summary: NullPointerException in OutputStreamAppender on logback reconfiguratiuon Key: LOGBACK-1362 URL: https://jira.qos.ch/browse/LOGBACK-1362 Project: logback Issue Type: Bug Components: logback-core Affects Versions: 1.2.3 Environment: reconfiguration of logback during slf4j start Reporter: Alexander Kudrevatykh Assignee: Logback dev list {noformat} 12:28:28,924 |-ERROR in ch.qos.logback.core.ConsoleAppender[console] - Appender [console] failed to append. java.lang.NullPointerException        at java.lang.NullPointerException        at     at ch.qos.logback.core.OutputStreamAppender.writeBytes(OutputStreamAppender.java:199)        at     at ch.qos.logback.core.OutputStreamAppender.subAppend(OutputStreamAppender.java:231)        at     at ch.qos.logback.core.OutputStreamAppender.append(OutputStreamAppender.java:102)        at     at ch.qos.logback.core.UnsynchronizedAppenderBase.doAppend(UnsynchronizedAppenderBase.java:84)        at     at ch.qos.logback.core.spi.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:51)        at     at ch.qos.logback.classic.Logger.appendLoopOnAppenders(Logger.java:270)        at     at ch.qos.logback.classic.Logger.callAppenders(Logger.java:257)        at     at ch.qos.logback.classic.Logger.buildLoggingEventAndAppend(Logger.java:421)        at     at ch.qos.logback.classic.Logger.filterAndLog_0_Or3Plus(Logger.java:383)        at     at ch.qos.logback.classic.Logger.log(Logger.java:775)        at     at sun.reflect.GeneratedMethodAccessor15.invoke(Unknown Source)        at     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)        at     at java.lang.reflect.Method.invoke(Method.java:498)        at     at org.slf4j.helpers.SubstituteLogger.log(SubstituteLogger.java:374)        at     at org.slf4j.LoggerFactory.replaySingleEvent(LoggerFactory.java:229)        at     at org.slf4j.LoggerFactory.replayEvents(LoggerFactory.java:198)        at     at org.slf4j.LoggerFactory.bind(LoggerFactory.java:142)        at     at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:124)        at     at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:345)        at     at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:290)        at     at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:316){noformat} In our environment sometimes we receive reconfiguration event of logback (via zookeeper) during sl4j initialization. During such reconfiguration we receieve such NPE. I think this is happens because race-condition in OutputStreamAppender thread1 subAppend() - call checkClosed() returns false thread2 LoggerContext.reset() called, that translates to OutputStreamAppender.stop() thread1 call writeBytes - throws NPE, becase appender already closed possible unit test that reproduces NPE {code:java} package ch.qos.logback.core;   import java.io.IOException; import java.io.OutputStream;   import org.junit.Test;   import ch.qos.logback.core.encoder.EncoderBase;     public class TestAppender {               @Test        public void testAppender() throws InterruptedException {              OutputStreamAppender<Object> appender = new OutputStreamAppender<Object>() {                     @Override                     public void addError(String msg, Throwable ex) {                            throw new RuntimeException(msg, ex);                     }              };              appender.setEncoder(new EncoderBase<Object>() {                       @Override                     public byte[] headerBytes() {                            return null;                     }                       @Override                     public byte[] encode(Object event) {                            try {                                   Thread.sleep(1000);                            } catch (InterruptedException e) {                                   // TODO Auto-generated catch block                                   e.printStackTrace();                            }                            return new byte[] {'A'};                     }                       @Override                     public byte[] footerBytes() {                            // TODO Auto-generated method stub                            return null;                     }              });              appender.setOutputStream(new OutputStream() {                                         @Override                     public void write(int b) throws IOException {                            throw new RuntimeException("not closed appender");                     }              });              appender.start();                           Thread t = new Thread(new Runnable() {                                         @Override                     public void run() {                            try {                                   Thread.sleep(500);                            } catch (InterruptedException e) {                                   // TODO Auto-generated catch block                                   e.printStackTrace();                            }                            appender.stop();                     }              });              t.start();              appender.doAppend(new Object());              t.join();        }   }{code}     -- This message was sent by Atlassian JIRA (v7.3.1#73012)