引言
tomcat属于web应用服务器,当我们的应用服务器关闭后,但是有些java class/thread/threadLocal等依然存活,当再次reload后,就会导致内存的溢出.为了避免这种严重的内存leak问题,tomcat做了一些内存溢出检测.
server.xml
<!-- Prevent memory leaks due to use of particular java/javax APIs--> <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener"/> <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener"/> <Listener className="org.apache.catalina.core.ThreadLocalLeakPreventionListener"/>
虽然tomcat做了这些检测并试图stop这些存活的引用,但是不是强制的,比如一些请求或线程,当应用关闭的时候,还在处理中,这时tomcat不会去关闭.这就需要tomcat强制关闭或依赖对应的框架来关闭.
项目中遇到类似问题
Q1: org.apache.catalina.loader.WebappClassLoaderclearReferencesJdbc SEVERE:The web application [/myapp] registered the JDBC driver[com.mysql.jdbc.Driver] but failed to unregister it when the web applicationwas stopped. To prevent a memory leak, the JDBC Driver has been forciblyunregistered. A1: https://stackoverflow.com/questions/15632153/tomcat7-jdbc-datasource-this-is-very-likely-to-create-a-memory-leak 需要把项目中使用的jdbc驱动包放到tomcat/lib Q2: org.apache.catalina.loader.WebappClassLoaderclearReferencesThreads SEVERE: The web application [/myapp] appears to have started athread named [Abandoned connection cleanup thread] but has failed to stop it.This is very likely to create a memory leak. A2: https://stackoverflow.com/questions/24850091/the-web-application-registered-the-jdbc-driver-com-mysql-jdbc-driver-but-fa Q3: SEVERE:The web application [/myapp] appears to have started a thread named [MySQL StatementCancellation Timer] but has failed to stop it. This is very likely to create amemory leak. A3: https://stackoverflow.com/questions/10615118/how-to-solve-memory-leak-problems 这是mysql jdbc 驱动包的一个BUG(SUNVM), https://bugs.mysql.com/bug.php?id=36565 version 5.1.27之后的版本解决了这个问题. Q4: org.apache.catalina.loader.WebappClassLoadercheckThreadLocalMapForLeaks SEVERE: The web application [/myapp] created a ThreadLocal with keyof type [java.lang.ThreadLocal] (value [java.lang.ThreadLocal@681f8054]) and avalue of type [com.alibaba.druid.wall.spi.WallVisitorUtils.WallTopStatementContext](value[com.alibaba.druid.wall.spi.WallVisitorUtils$WallTopStatementContext@117d5a14])but failed to remove it when the web application was stopped. Threads are goingto be renewed over time to try and avoid a probable memory leak. A4: 关闭druid的自带监测功能.
tomcat 释放引用的主要分类
1. org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc
http://hongjiang.info/tomcat-jdbc-leak-prevention/
把JDBC driver放到tomcat/lib下,并删除项目的jdbc driver.
2. org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
http://hongjiang.info/tomcat-clear-references-threads/
3. org.apache.catalina.loader.WebappClassLoader checkThreadLocalMapForLeaks
http://hongjiang.info/tomcat-clear-references-threadlocal/
4. clearReferencesRmiTargets
5.clearReferencesStaticFinal
6.clearReferencesResourceBundles
protected void clearReferences() { // De-register any remaining JDBC drivers clearReferencesJdbc(); // Stop any threads the web application started clearReferencesThreads(); // Check for leaks triggered by ThreadLocals loaded by this class loader checkThreadLocalsForLeaks(); // Clear RMI Targets loaded by this class loader clearReferencesRmiTargets(); // Null out any static or final fields from loaded classes, // as a workaround for apparent garbage collection bugs if (clearReferencesStatic) { clearReferencesStaticFinal(); } // Clear the IntrospectionUtils cache. IntrospectionUtils.clear(); // Clear the classloader reference in common-logging if (clearReferencesLogFactoryRelease) { org.apache.juli.logging.LogFactory.release(this); } // Clear the resource bundle cache // This shouldn‘t be necessary, the cache uses weak references but // it has caused leaks. Oddly, using the leak detection code in // standard host allows the class loader to be GC‘d. This has been seen // on Sun but not IBM JREs. Maybe a bug in Sun‘s GC impl? clearReferencesResourceBundles(); // Clear the classloader reference in the VM‘s bean introspector java.beans.Introspector.flushCaches(); }
tomcat graceful shutdown
https://dzone.com/articles/tomcats-graceful-shutdown
http://www.captaindebug.com/2013/09/tomcats-graceful-shutdown-with-daemons.html#.Wdxh9ltL_IU
参考文档:
http://hongjiang.info/tomcat-jdbc-leak-prevention/
http://hongjiang.info/tomcat-clear-references-threads/
http://hongjiang.info/tomcat-clear-references-threadlocal/
http://blog.csdn.net/will_awoke/article/details/38338519
http://www.cnblogs.com/lixiaojiao-hit/p/5095180.html
原文地址：http://881206524.blog.51cto.com/10315134/1971118
