Logback在Docker容器退出时抛出ConcurrentModificationException问题求助

应用作为独立Java程序运行时正常，但在Docker容器内退出时触发ConcurrentModificationException异常，堆栈跟踪如下：

Exception in thread "Logback shutdown hook [default]" java.util.ConcurrentModificationException
    at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1043)
    at java.base/java.util.ArrayList$Itr.next(ArrayList.java:997)
    at ch.qos.logback.classic.LoggerContext.fireOnReset(LoggerContext.java:323)
    at ch.qos.logback.classic.LoggerContext.reset(LoggerContext.java:226)
    at ch.qos.logback.classic.LoggerContext.stop(LoggerContext.java:348)
    at ch.qos.logback.core.hook.ShutdownHookBase.stop(ShutdownHookBase.java:39)
    at ch.qos.logback.core.hook.DelayingShutdownHook.run(DelayingShutdownHook.java:57)
    at java.base/java.lang.Thread.run(Thread.java:834)

Logback配置（logback-spring.xml） #

<?xml version="1.0" encoding="UTF-8"?>

<configuration>
    <!--See https://docs.spring.io/spring-boot/docs/current/reference/html/howto-logging.html -->
    <shutdownHook
            class="ch.qos.logback.core.hook.DelayingShutdownHook"/>
    <include resource="org/springframework/boot/logging/logback/defaults.xml"/>
    <appender name="CONSOLE_JSON" class="ch.qos.logback.core.ConsoleAppender">
        <encoder class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
            <layout class="ch.qos.logback.contrib.json.classic.JsonLayout">
                <jsonFormatter class="ch.qos.logback.contrib.jackson.JacksonJsonFormatter">
                    <!-- <prettyPrint>true</prettyPrint> -->
                </jsonFormatter>
                <timestampFormat>yyyy-MM-dd'T'HH:mm:ss.SSSXXX</timestampFormat>
                <includeContextName>false</includeContextName>
                <appendLineSeparator>true</appendLineSeparator>
            </layout>
            <charset>UTF-8</charset>
        </encoder>
    </appender>
    <appender name="ASYNCSTDOUT" class="ch.qos.logback.classic.AsyncAppender">
        <queueSize>5000</queueSize> <!-- Default is 256 -->
        <discardingThreshold>0</discardingThreshold> <!-- Instruction to drop events
            once the buffer reaches the max capacity. Default value is 20%.
            20 means drop lower event when has 20% capacity remaining -->
        <neverBlock>true</neverBlock><!-- default false. Setting it to true to
            cause the Appender not block the application and just drop the messages -->
        <maxFlushTime>5000</maxFlushTime> <!-- The default maximum queue flush time allowed during appender stop. If
            the worker takes longer than this time it will exit, discarding any remaining
            cartItems in the queue -->
        <appender-ref ref="CONSOLE_JSON"/>
    </appender>

    <logger name="org.springframework.web" level="INFO"/>

    <root level="INFO">
        <appender-ref ref="ASYNCSTDOUT"/>
    </root>

</configuration>

POM依赖构件 #

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.8</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>


    <dependencies>
      
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
            <version>2.5.8</version>
        </dependency>
     
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
            <version>1.2.3</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-access</artifactId>
            <version>1.2.3</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-sleuth</artifactId>
            <version>2.1.0.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <version>5.3.14</version>
        </dependency>
       
    
        <dependency>
            <groupId>net.logstash.logback</groupId>
            <artifactId>logstash-logback-encoder</artifactId>
            <version>6.6</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback.contrib</groupId>
            <artifactId>logback-jackson</artifactId>
            <version>0.1.5</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback.contrib</groupId>
            <artifactId>logback-json-classic</artifactId>
            <version>0.1.5</version>
        </dependency>
        
    </dependencies>

问题根源 #

异常发生在Logback关闭钩子遍历LoggerContext的监听器列表时，由于多线程并发修改非线程安全的ArrayList导致。Docker环境下JVM关闭流程与本地存在差异，触发了监听器在遍历过程中被修改的时序问题，而本地环境未复现该场景。

具体修复步骤 #

1. 升级Logback版本
   Logback 1.2.3存在监听器列表并发修改的bug，1.2.9及以上版本已修复该问题。将pom中Logback相关依赖版本升级到1.2.10（与Spring Boot 2.5.8兼容）：

   <dependency>
       <groupId>ch.qos.logback</groupId>
       <artifactId>logback-core</artifactId>
       <version>1.2.10</version>
   </dependency>
   <dependency>
       <groupId>ch.qos.logback</groupId>
       <artifactId>logback-classic</artifactId>
       <version>1.2.10</version>
   </dependency>
   <dependency>
       <groupId>ch.qos.logback</groupId>
       <artifactId>logback-access</artifactId>
       <version>1.2.10</version>
   </dependency>
   

2. 调整Logback关闭钩子配置
   若暂时无法升级版本，可尝试两种调整方式：

   • 移除自定义DelayingShutdownHook，使用Spring Boot默认的关闭处理逻辑：

     <!-- 注释或删除该行 -->
     <!-- <shutdownHook class="ch.qos.logback.core.hook.DelayingShutdownHook"/> -->
     

   • 增加关闭延迟时间，确保异步日志队列完全刷写完成后再执行关闭：

     <shutdownHook class="ch.qos.logback.core.hook.DelayingShutdownHook">
         <delay>10000</delay> <!-- 设置10秒延迟 -->
     </shutdownHook>
     

3. 升级Spring Cloud Sleuth版本
   当前使用的Sleuth 2.1.0与Spring Boot 2.5.8版本不匹配（对应Spring Cloud版本应为2020.0.x），升级到兼容版本可避免关闭时修改Logback监听器：

   <dependency>
       <groupId>org.springframework.cloud</groupId>
       <artifactId>spring-cloud-starter-sleuth</artifactId>
       <version>3.0.4</version>
   </dependency>
   

验证 #

修改后重新构建Docker镜像，运行容器并正常退出，检查日志是否不再出现ConcurrentModificationException异常。

内容的提问来源于stack exchange，提问作者Amol Aggarwal