java - 在 Web 应用程序中使用 javassist 阻塞线程

Question

有人可以帮助我并解释到底发生了什么，看看下面的线程转储。这是一个在 Tomcat 7 上运行的 Web 应用程序，我们遇到一些请求没有得到响应:

"ajp-bio-8012-exec-161" daemon prio=10 tid=0x00007fe170603000 nid=0x344f runnable [0x00007fe174fae000]
   java.lang.Thread.State: RUNNABLE
    at java.security.AccessController.doPrivileged(Native Method)
    at java.io.FilePermission.init(FilePermission.java:209)
    at java.io.FilePermission.<init>(FilePermission.java:285)
    at java.lang.SecurityManager.checkRead(SecurityManager.java:888)
    at java.io.File.exists(File.java:808)
    at sun.misc.URLClassPath$FileLoader.getResource(URLClassPath.java:1080)
    at sun.misc.URLClassPath$FileLoader.findResource(URLClassPath.java:1047)
    at sun.misc.URLClassPath.findResource(URLClassPath.java:176)
    at java.net.URLClassLoader$2.run(URLClassLoader.java:551)
    at java.net.URLClassLoader$2.run(URLClassLoader.java:549)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findResource(URLClassLoader.java:548)
    at java.lang.ClassLoader.getResource(ClassLoader.java:1147)
    at java.lang.ClassLoader.getResource(ClassLoader.java:1142)
    at org.apache.catalina.loader.WebappClassLoader.getResource(WebappClassLoader.java:1445)
    at java.lang.Class.getResource(Class.java:2142)
    at javassist.ClassClassPath.find(ClassClassPath.java:84)
    at javassist.ClassPoolTail.find(ClassPoolTail.java:317)
    at javassist.ClassPool.find(ClassPool.java:495)
    at javassist.ClassPool.createCtClass(ClassPool.java:479)
    at javassist.ClassPool.get0(ClassPool.java:445)
    - locked <0x00000000db6cdb48> (a javassist.ClassPool)
    at javassist.ClassPool.get(ClassPool.java:414)
    at javassist.compiler.MemberResolver.lookupClass0(MemberResolver.java:425)
    at javassist.compiler.MemberResolver.lookupClass(MemberResolver.java:389)
    at javassist.compiler.MemberResolver.lookupClassByJvmName(MemberResolver.java:310)
    at javassist.compiler.MemberResolver.lookupClass(MemberResolver.java:327)
    at javassist.compiler.MemberResolver.lookupClass(MemberResolver.java:314)
    at javassist.compiler.Javac.compileField(Javac.java:122)
    at javassist.compiler.Javac.compile(Javac.java:91)
    at javassist.CtField.make(CtField.java:163)
    at com.mycompany.validation.util.BeanGenerator.addProperty(BeanGenerator.java:157)
    ...
    at java.lang.Thread.run(Thread.java:745)


"ajp-bio-8012-exec-12" daemon prio=10 tid=0x0000000000c49800 nid=0x3d99 waiting for monitor entry [0x00007fe1756b7000]
   java.lang.Thread.State: BLOCKED (on object monitor)
    at javassist.ClassPool.get0(ClassPool.java:432)
    - waiting to lock <0x00000000db6cdb48> (a javassist.ClassPool)
    at javassist.ClassPool.get(ClassPool.java:414)
    at javassist.compiler.MemberResolver.lookupClass0(MemberResolver.java:425)
    at javassist.compiler.MemberResolver.lookupClass(MemberResolver.java:389)
    at javassist.compiler.MemberResolver.lookupClassByJvmName(MemberResolver.java:310)
    at javassist.compiler.MemberResolver.lookupClass(MemberResolver.java:327)
    at javassist.compiler.MemberResolver.lookupClass(MemberResolver.java:314)
    at javassist.compiler.Javac.compileField(Javac.java:122)
    at javassist.compiler.Javac.compile(Javac.java:91)
    at javassist.CtField.make(CtField.java:163)
    at com.mycompany.validation.util.BeanGenerator.addProperty(BeanGenerator.java:157)
    ...
    at java.lang.Thread.run(Thread.java:745)



"ajp-bio-8012-exec-5" daemon prio=10 tid=0x0000000001603800 nid=0x7c77 waiting for monitor entry [0x00007fe174aaa000]
   java.lang.Thread.State: BLOCKED (on object monitor)
    at javassist.ClassPool.makeClass(ClassPool.java:621)
    - waiting to lock <0x00000000db6cdb48> (a javassist.ClassPool)
    at javassist.ClassPool.makeClass(ClassPool.java:606)
    at com.mycompany.validation.util.BeanGenerator.init(BeanGenerator.java:334)
    ...
    at java.lang.Thread.run(Thread.java:745)    

我不是线程转储方面的专家，只是想知道如何解决这个问题。

第一个线程是否锁定了其他两个请求线程正在等待解锁的对象 (ClassPool)？为什么被锁了？我必须同步吗？如何同步？

感谢任何提示!

Answer 1

您的应用程序中有一个 ClassPool，其监视器 ID 为 0x00000000db6cdb48。

如果您看到 ClassPool.get0 的方法签名:

protected synchronized CtClass get0(String classname, boolean useCache)

所以它是同步的。我想您只是使用了 ClassPool.getDefault()。您必须知道此方法返回单个实例，因此您的所有调用都将被同步。

为每个线程创建一个新的池(例如new ClassPool(ClassPool.getDefault()))然后就可以了。

除此之外，您还可以检查您的安全管理器，了解为什么需要这么长时间。