为什么Tomcat使用共享库开始这么慢？

Question

问题

我们Tomcat 7.0.35运行了25个webapps,它们共享相同的库,具有相同的版本(保证永远不会改变!).我想,而不是每个项目加载相同的库,我可以移动它们${catalina.home}/lib导致所需的内存负载减少.

然而,这是有代价的:每个webapp的部署时间从5秒增加到2分钟,这是不可行的!

我做了一些阅读(例如Class Loader HOW-TO),遗憾的是我无法找到减少启动时间的方法.有没有办法解决这个问题？

请求的分析信息

我跑jstack,并jvisualvm在两种不同的情况,我会在这里提出一些调查结果(请让我知道如果你需要更多的信息):

似乎为每个项目特定的库加载: org.apache.catalina.loader.WebappClassLoader.findResourceInternal
运行该方法的线程的jstack输出:

"localhost-startStop-1" daemon prio=10 tid=0x00007f17f8001800 nid=0x13b8 runnable [0x00007f183c800000]
   java.lang.Thread.State: RUNNABLE
        at java.text.MessageFormat.subformat(MessageFormat.java:1250)
        at java.text.MessageFormat.format(MessageFormat.java:819)
        at org.apache.naming.StringManager.getString(StringManager.java:145)
        at org.apache.naming.resources.BaseDirContext.lookup(BaseDirContext.java:500)
        at org.apache.naming.resources.ProxyDirContext.lookup(ProxyDirContext.java:310)
        at org.apache.catalina.loader.WebappClassLoader.findResourceInternal(WebappClassLoader.java:3011)
        at org.apache.catalina.loader.WebappClassLoader.findResource(WebappClassLoader.java:1262)
        at org.apache.catalina.loader.WebappClassLoader.getResourceAsStream(WebappClassLoader.java:1499)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2302)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2294)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2308)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2291)
        at org.apache.catalina.startup.ContextConfig.checkHandlesTypes(ContextConfig.java:2197)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:2154)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsJar(ContextConfig.java:2034)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsUrl(ContextConfig.java:1990)
        at org.apache.catalina.startup.ContextConfig.processAnnotations(ContextConfig.java:1976)
        at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1326)
        at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:882)
        - locked <0x00000007f52f3ec0> (a org.apache.catalina.startup.ContextConfig)
        at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:379)
        at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
        at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5343)
        - locked <0x00000007f52f3bb8> (a org.apache.catalina.core.StandardContext)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
        - locked <0x00000007f52f3bb8> (a org.apache.catalina.core.StandardContext)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:902)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:879)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:636)
        at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1236)
        at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1877)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
        - <0x00000007846dfc70> (a java.util.concurrent.ThreadPoolExecutor$Worker)

项目之间共享的库似乎被加载:
at org.apache.catalina.loader.WebappClassLoader.getResourceAsStream这导致令人难以置信的部署时间.在项目部署期间,JVisualVM为此方法显示98%+"自我时间".
运行该方法的线程的jstack输出:

"localhost-startStop-1" daemon prio=10 tid=0x00007f6280001000 nid=0x6ba3 runnable [0x00007f62c4950000]
   java.lang.Thread.State: RUNNABLE
        at java.lang.String.intern(Native Method)
        at java.util.jar.Attributes$Name.<init>(Attributes.java:466)
        at java.util.jar.Attributes.putValue(Attributes.java:168)
        at java.util.jar.Attributes.read(Attributes.java:421)
        at java.util.jar.Manifest.read(Manifest.java:251)
        at sun.security.util.SignatureFileVerifier.processImpl(SignatureFileVerifier.java:252)
        at sun.security.util.SignatureFileVerifier.process(SignatureFileVerifier.java:239)
        at java.util.jar.JarVerifier.processEntry(JarVerifier.java:307)
        at java.util.jar.JarVerifier.update(JarVerifier.java:218)
        at java.util.jar.JarFile.initializeVerifier(JarFile.java:345)
        at java.util.jar.JarFile.getInputStream(JarFile.java:412)
        - locked <0x00000007e8e9d890> (a sun.net.www.protocol.jar.URLJarFile)
        at sun.net.www.protocol.jar.JarURLConnection.getInputStream(JarURLConnection.java:162)
        at java.net.URLClassLoader.getResourceAsStream(URLClassLoader.java:233)
        at org.apache.catalina.loader.WebappClassLoader.getResourceAsStream(WebappClassLoader.java:1528)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2302)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2294)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2308)
        at org.apache.catalina.startup.ContextConfig.populateJavaClassCache(ContextConfig.java:2294)
        at org.apache.catalina.startup.ContextConfig.checkHandlesTypes(ContextConfig.java:2197)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsStream(ContextConfig.java:2154)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsJar(ContextConfig.java:2034)
        at org.apache.catalina.startup.ContextConfig.processAnnotationsUrl(ContextConfig.java:1990)
        at org.apache.catalina.startup.ContextConfig.processAnnotations(ContextConfig.java:1976)
        at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1326)
        at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:882)
        - locked <0x00000007858db6e0> (a org.apache.catalina.startup.ContextConfig)
        at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:379)
        at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:118)
        at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:91)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5346)
        - locked <0x00000007858db318> (a org.apache.catalina.core.StandardContext)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
        - locked <0x00000007858db318> (a org.apache.catalina.core.StandardContext)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:902)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:879)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:636)
        at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1236)
        at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1877)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
        - <0x000000078460e618> (a java.util.concurrent.ThreadPoolExecutor$Worker)

Answer 1

WebappClassLoader 首先搜索自己的类路径。因此，对于不在本地类路径中的每个类，将查看所有 jar 文件。只有这样它才会查看公共类加载器的委托。

假设查看所有 war 的 jar 需要 x 时间，而对于其父类加载器的 jar 则需要 y 时间。

平均而言，从正确的类加载器加载一个类所花费的时间是扫描所有内容所需时间的一半。

从 WebappClassLoader 加载类将花费 x/2 时间。

从父类加载器加载一个类需要 x + y/2。

根据 x 和 y，您可以更改类加载器的使用顺序。如果 y 大于 x，您应该保留默认设置，如果 x 大于您可以尝试反转查找顺序。如果这样做，从公共类加载器加载类将花费 y/2 时间，但从 WebappClassLoader 加载类将花费 y + x/2 时间。

WebbappClassLoader 有一个 delegate 属性，将其设置为 true 应该可以解决问题。查看通用属性