java - 为什么 Log4j2 的 RollingFile 附加程序会阻止独立应用程序终止 60 秒？

Question

这段代码重现了我认为是 Log4j2 的错误。这是一个简单的循环，使用两个附加程序记录 2000 条消息:控制台附加器和滚动文件的滚动文件附加器每 5Kb。这个限制故意设置得很低，以重现我认为的错误。

这是代码。

package bug;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class Example {

    private static final Logger logger = LogManager.getLogger(Example.class);

    public static void main(String[] args) throws InterruptedException {
        for(int i = 0; i<2000; i++){
            logger.info("This is log message #{}.", i);
            Thread.sleep(0);
        }
    }

}

这是log4j2.xml配置文件。

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="TRACE">
    <Appenders>
        <Console name="stdout" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} %p %m%n"/>
        </Console>
        <RollingFile name="roll-by-size"
                     fileName="target/log4j2/roll-by-size/app.log"
                     filePattern="target/log4j2/roll-by-size/app.%i.log.gz"
                     ignoreExceptions="false"
                     append="false">
            <PatternLayout>
                <Pattern>%d{yyyy-MM-dd HH:mm:ss} %p %m%n</Pattern>
            </PatternLayout>
            <Policies>
                <OnStartupTriggeringPolicy/>
                <SizeBasedTriggeringPolicy
                        size="5 KB"/>
            </Policies>
        </RollingFile>
    </Appenders>
    <Loggers>
        <Logger name="bug" level="TRACE">
            <AppenderRef ref="roll-by-size"/>
        </Logger>
        <Root level="DEBUG">
            <AppenderRef ref="stdout"/>
        </Root>
    </Loggers>
</Configuration>

奇怪的是，当应用程序启动时，您将在控制台中看到此日志。

2016-12-22 22:12:36 INFO This is log message #1993.
2016-12-22 22:12:36 INFO This is log message #1994.
2016-12-22 22:12:36 INFO This is log message #1995.
2016-12-22 22:12:36 INFO This is log message #1996.
2016-12-22 22:12:36 INFO This is log message #1997.
2016-12-22 22:12:36 INFO This is log message #1998.
2016-12-22 22:12:36 INFO This is log message #1999.
2016-12-22 22:13:36,380 pool-1-thread-1 DEBUG Stopping LoggerContext[name=60199c81, org.apache.logging.log4j.core.LoggerContext@4597ec68]
2016-12-22 22:13:36,380 pool-1-thread-1 DEBUG Stopping LoggerContext[name=60199c81, org.apache.logging.log4j.core.LoggerContext@4597ec68]...
2016-12-22 22:13:36,381 pool-1-thread-1 TRACE Unregistering 1 MBeans: [org.apache.logging.log4j2:type=60199c81]
2016-12-22 22:13:36,381 pool-1-thread-1 TRACE Unregistering 1 MBeans: [org.apache.logging.log4j2:type=60199c81,component=StatusLogger]
2016-12-22 22:13:36,381 pool-1-thread-1 TRACE Unregistering 1 MBeans: [org.apache.logging.log4j2:type=60199c81,component=ContextSelector]
2016-12-22 22:13:36,381 pool-1-thread-1 TRACE Unregistering 2 MBeans: [org.apache.logging.log4j2:type=60199c81,component=Loggers,name=bug, org.apache.logging.log4j2:type=60199c81,component=Lo
ggers,name=]
2016-12-22 22:13:36,381 pool-1-thread-1 TRACE Unregistering 2 MBeans: [org.apache.logging.log4j2:type=60199c81,component=Appenders,name=roll-by-size, org.apache.logging.log4j2:type=60199c81,c
omponent=Appenders,name=stdout]
2016-12-22 22:13:36,382 pool-1-thread-1 TRACE Unregistering but no MBeans found matching 'org.apache.logging.log4j2:type=60199c81,component=AsyncAppenders,name=*'
2016-12-22 22:13:36,382 pool-1-thread-1 TRACE Unregistering but no MBeans found matching 'org.apache.logging.log4j2:type=60199c81,component=AsyncLoggerRingBuffer'
2016-12-22 22:13:36,382 pool-1-thread-1 TRACE Unregistering but no MBeans found matching 'org.apache.logging.log4j2:type=60199c81,component=Loggers,name=*,subtype=RingBuffer'
2016-12-22 22:13:36,382 pool-1-thread-1 TRACE Stopping XmlConfiguration[location=C:\Users\danidemi\workspace\bug-log4j2-hanging-up-before-shutdown\target\classes\log4j2.xml]...
2016-12-22 22:13:36,382 pool-1-thread-1 TRACE XmlConfiguration notified 3 ReliabilityStrategies that config will be stopped.
2016-12-22 22:13:36,382 pool-1-thread-1 TRACE XmlConfiguration stopping 2 LoggerConfigs.
2016-12-22 22:13:36,382 pool-1-thread-1 TRACE XmlConfiguration stopping root LoggerConfig.
2016-12-22 22:13:36,382 pool-1-thread-1 TRACE XmlConfiguration notifying ReliabilityStrategies that appenders will be stopped.
2016-12-22 22:13:36,382 pool-1-thread-1 TRACE XmlConfiguration stopping remaining Appenders.
2016-12-22 22:13:36,383 pool-1-thread-1 DEBUG Shutting down RollingFileManager target/log4j2/roll-by-size/app.log
2016-12-22 22:13:36,383 pool-1-thread-1 DEBUG Shut down RollingFileManager target/log4j2/roll-by-size/app.log, all resources released: true
2016-12-22 22:13:36,383 pool-1-thread-1 DEBUG Shutting down OutputStreamManager SYSTEM_OUT.false.false
2016-12-22 22:13:36,383 pool-1-thread-1 DEBUG Shut down OutputStreamManager SYSTEM_OUT.false.false, all resources released: true
2016-12-22 22:13:36,384 pool-1-thread-1 TRACE XmlConfiguration stopped 2 remaining Appenders.
2016-12-22 22:13:36,384 pool-1-thread-1 TRACE XmlConfiguration cleaning Appenders from 3 LoggerConfigs.
2016-12-22 22:13:36,384 pool-1-thread-1 DEBUG Stopped XmlConfiguration[location=C:\Users\danidemi\workspace\bug-log4j2-hanging-up-before-shutdown\target\classes\log4j2.xml] OK
2016-12-22 22:13:36,385 pool-1-thread-1 DEBUG Stopped LoggerContext[name=60199c81, org.apache.logging.log4j.core.LoggerContext@4597ec68]...

奇怪的是最后一条日志是在某个时间发出的...

2016-12-22 22:12:36 INFO This is log message #1999.

但是 log4j2 的关闭在最后一条“业务”日志消息后恰好一分钟开始。

2016-12-22 22:13:36,380 pool-1-thread-1 DEBUG Stopping LoggerContext[name=60199c81, org.apache.logging.log4j.core.LoggerContext@4597ec68]

这就是问题所在!业务逻辑终止，但 log4j2 等待一分钟才允许应用程序停止!为什么 ？我希望应用程序能够像人们所期望的那样立即停止。

我调查了一下...这 60 秒的延迟似乎或多或少是独立的根据记录的消息数量。

但是，如果您更改 log4j2.xml，将大小从 5Kb 增加...

<Policies>
    <OnStartupTriggeringPolicy/>
    <SizeBasedTriggeringPolicy size="5 KB"/>
</Policies>

至 5Mb...

<Policies>
    <OnStartupTriggeringPolicy/>
    <SizeBasedTriggeringPolicy size="5 MB"/>
</Policies>

...这使得应用程序在最后一条日志消息之后立即停止。5Mb 是一个足够大的限制，不需要滚动实际发生。所以我认为滚动本身在某种程度上导致了这种延迟的发生。我认为这是一个错误，但是...你觉得怎么样？

我在 GitHub 上建立了一个小型 Maven 项目这证明了我在这里试图解释的内容。

Answer 1

谢谢您raising this issue到 Log4j2 社区。

根本原因是 Log4j 创建了两个 ThreadPoolExecutor，一个守护进程和一个非守护进程。这些执行器是使用默认设置创建的，该设置将线程 keepAliveTime 设置为一分钟。

在示例中，应用程序在触发翻转后立即关闭。翻转会在非守护程序执行程序的后台线程中压缩旧文件。因为执行器使该线程保持 Activity 状态一分钟，并且这是一个非守护线程，所以整个应用程序保持 Activity 状态一分钟。

这只会影响翻转后立即退出的应用程序。

2016-12-26 更新:此问题已修复。从 2.8 开始，非守护线程默认将有更短的 keepAliveTime(一秒)。