tomcat shutdown后清理工作出现的异常

lrx182125

　　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
  
  
  
  　　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/
　　  https://stackoverflow.com/questions/15632153/tomcat7-jdbc-datasource-this-is-very-likely-to-create-a-memory-leak
　　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