Log4j2 AsyncAppender 线程在 tomcat 取消部署时不会死，导致内存泄漏

Question

The stack I am using at the moment is:

• log4j2 rc1
• spring 3.2 core and web
• tomcat 7.0.47
• java 1.6.0_45
• Windows 7

I don't have the ability to alter the tomcat version or java version and I would prefer not to alter the log4j version and spring version.

Essentially, when I undeploy my webapp I receieve a SEVERE warning saying:

SEVERE: The web application [/MyApp] appears to have started a thread named
[AsyncAppender-AsyncFile] but has failed to stop it. This is very likely to 
create a memory leak

I can confirm that it does create a memory leak and this is what I am trying to fix.

So far I have attempted to create a custom ServletContextListener which contains the following code:

@Override
public void contextDestroyed(ServletContextEvent event) {
    System.out.println("Shutting down logger");
    try {
        ((Log4jWebSupport) event.getServletContext().getAttribute(
            Log4jWebSupport.SUPPORT_ATTRIBUTE)).clearLoggerContext();
        ((LifeCycle) LogManager.getContext()).stop();
    } catch (Exception e) {

    }
}

None of these two lines seems to fix the problem, however I can confirm that this code is being executed due to my sysout statement appearing in the tomcat console.

I am using log4j2 through an interceptor which I am setting up using Spring

<mvc:interceptors>
    <mvc:interceptor>
        <mvc:mapping path="/**" />
        <ref bean="LoggingInterceptor"/>
    </mvc:interceptor>
</mvc:interceptors>
<bean id="LoggingInterceptor" class="MyLoggerClass">

The interceptor works correctly and the logs appear where I expect them to. My implementation of the logger is:

private static Logger log = LogManager.getLogger("MetricLogger");

public void log(LogPayload payload) {
    if(payload != null){
        log.info(payload.get());
    }
}

Where LogPayload.get() returns a String.

As I am using the logging facility across multiple webapps I have created a separate jar file containing this and the classes recording the measurements. I have included this using maven and I compile it into the final war file I deploy to tomcat. This war file is included on a per app basis and is not included in the global tomcat/lib folder.

Does anyone have any insight as to why I get my memory leak issue and what the possible solutions are to fixing this?

Many thanks for your help and please let me know if you need further information.

Answer 1

The solution to this that I have so far found is that I need to include the following snippet in the web.xml.

<listener>
    <listener-class>org.apache.logging.log4j.core.web.Log4jServletContextListener</listener-class>
</listener>

<filter>
    <filter-name>log4jServletFilter</filter-name>
    <filter-class>org.apache.logging.log4j.core.web.Log4jServletFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>log4jServletFilter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>FORWARD</dispatcher>
    <dispatcher>INCLUDE</dispatcher>
    <dispatcher>ERROR</dispatcher>
</filter-mapping>

This is specific to servlet spec 2.5. This seems to resolve the memory leak issue.

Answer 2

Adding the below snippet worked for me to get rid of memory leak due to Async-Appender threads not getting shut down even after the application shutdown. Thank you @kipper_t.

<listener>
    <listener-class>org.apache.logging.log4j.core.web.Log4jServletContextListener</listener-class>
</listener>

<filter>
    <filter-name>log4jServletFilter</filter-name>
    <filter-class>org.apache.logging.log4j.core.web.Log4jServletFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>log4jServletFilter</filter-name>
    <url-pattern>/*</url-pattern>

Answer 3

In case you are facing this issue recently you should note the following:

If you are using servlet 3.0+ and tomcat > 7.0.43 or Tomcat 8 there are no configuration needed, you just have to provide the correct maven dependencies to make log4j2 aware of running in a webcontainer like the following (in addition we use slf4j):

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.30</version>
</dependency>

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-api</artifactId>
    <version>2.11.0</version>
</dependency>

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.11.0</version>
</dependency>

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-web</artifactId>
    <version>2.11.0</version>
</dependency>

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-slf4j-impl</artifactId>
    <version>2.11.0</version>
</dependency>

Since in our case the log4j-web artifact was missing we faced the same warning which said "... started a thread named [AsyncAppender-AsyncFile] but has failed to stop it ..."

After providing the mentioned dependencies the warning is gone.

you can read more about requirements here