线程陷入getDeclaredConstructors的可能原因？

Question

对于我们的应用程序的一次安装,我们一直看到生产中的问题被用户报告为"系统变慢"或"请求永不返回".最后,服务器必须重新启动.我们有几个这样的事件,每晚重启服务器似乎是一个解决方法.

我们的应用程序大量使用动态类加载(存储在数据库中的.jar文件作为blob)和反射.环境细节:

• Java 1.7.021
• 操作系统:Linux(2.6.32-504.16.2.el6.x86_64)
• JBoss EAP 6.2
• Appdynamics正在使用
• 内存和gc设置:-XX:PermSize = 256m -XX:MaxPermSize = 2560m -Xms2048m -Xmx10240m -server -XX:+ UseParallelGC -XX:+ UseParallelOldGC

我们切换到了

• Java 1.7.080
• -XX:+ UseG1GC

但看起来我们仍然面临着这个问题.

我们在logfiles,heapdumps,threadumps和gc日志中看到的内容如下所示

• 我们没有看到任何OutOfMemory错误
• Heap和PermGend的内存消耗似乎没问题(堆和perm gen未完全使用)
• 使用Java 1.7.021和parallelGC,我们看到了几个长时间运行(5分钟)的Full GC - 在切换到G1GC后这似乎不再发生(这正是我们所期望的)
• 我们没有在日志中看到任何与CodeCache相关的警告

我们看到的是

• 对于某些事件,heapdump中DelegatingClassLoaders的数量约为5000,而其他事件则约为10万.
• 在用户初始报告系统变慢之后,状态为RUNNABLE且正在处理"getDeclaredConstructors0"的线程数正在增加(从开头只有两个增加到50左右.线程似乎"挂起"了多个小时的相同位置(他们处于RUNNABLE状态).

有关该线程组的摘录,请参见下文:

"http-xxx:8443-141" daemon prio=10 tid=0x00007efe9412f000 nid=0x64fb runnable [0x00007efe1ba8a000]
   java.lang.Thread.State: RUNNABLE
    at java.lang.Class.getDeclaredConstructors0(Native Method)
    at java.lang.Class.privateGetDeclaredConstructors(Class.java:2413)
    at java.lang.Class.getConstructor0(Class.java:2723)
    at java.lang.Class.newInstance0(Class.java:345)
    at java.lang.Class.newInstance(Class.java:327)
    at sun.reflect.MethodAccessorGenerator$1.run(MethodAccessorGenerator.java:399)
    at sun.reflect.MethodAccessorGenerator$1.run(MethodAccessorGenerator.java:396)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.reflect.MethodAccessorGenerator.generate(MethodAccessorGenerator.java:395)
    at sun.reflect.MethodAccessorGenerator.generateMethod(MethodAccessorGenerator.java:77)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:46)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    [application code]

"http-xxx:8443-138" daemon prio=10 tid=0x00007efe9412a000 nid=0x64ed runnable [0x00007efe1c397000]
   java.lang.Thread.State: RUNNABLE
    at java.lang.Class.getDeclaredConstructors0(Native Method)
    at java.lang.Class.privateGetDeclaredConstructors(Class.java:2413)
    at java.lang.Class.getConstructor0(Class.java:2723)
    at java.lang.Class.newInstance0(Class.java:345)
    at java.lang.Class.newInstance(Class.java:327)
    at sun.reflect.MethodAccessorGenerator$1.run(MethodAccessorGenerator.java:399)
    at sun.reflect.MethodAccessorGenerator$1.run(MethodAccessorGenerator.java:396)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.reflect.MethodAccessorGenerator.generate(MethodAccessorGenerator.java:395)
    at sun.reflect.MethodAccessorGenerator.generateMethod(MethodAccessorGenerator.java:77)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:46)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.mvel2.PropertyAccessor.set(PropertyAccessor.java:350)
    at org.mvel2.PropertyAccessor.set(PropertyAccessor.java:134)
    at org.mvel2.MVEL.setProperty(MVEL.java:1088)   
    [application code]

更新到Java 1.7.80/G1Gc后的情况似乎相似.不幸的是没有可用的线程,只是日志中的wicket警告)

2016-03-10 15:00:39,009 WARN  [http-xxx:7443-23] org.apache.wicket.page.PageAccessSynchronizer: Thread 'http-xxx:7443-23' failed to acquire lock to page with id '28', attempted for 3 minutes out of allowed 3 minutes. The thread that holds the lock has name 'http-xxx:7443-18'.
2016-03-10 15:00:39,017 WARN  [http-xxx:7443-23] org.apache.wicket.page.PageAccessSynchronizer: "http-xxx:7443-18" daemon prio=5 tid=8950 state=RUNNABLE 
org.apache.wicket.util.lang.Threads$ThreadDump
    at java.lang.Class.getDeclaredConstructors0(Native Method)
    at java.lang.Class.privateGetDeclaredConstructors(Class.java:2595)
    at java.lang.Class.getConstructor0(Class.java:2895)
    at java.lang.Class.newInstance(Class.java:354)
    at sun.reflect.MethodAccessorGenerator$1.run(MethodAccessorGenerator.java:399)
    at sun.reflect.MethodAccessorGenerator$1.run(MethodAccessorGenerator.java:396)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.reflect.MethodAccessorGenerator.generate(MethodAccessorGenerator.java:395)
    at sun.reflect.MethodAccessorGenerator.generateSerializationConstructor(MethodAccessorGenerator.java:113)
    at sun.reflect.ReflectionFactory.newConstructorForSerialization(ReflectionFactory.java:331)
    at java.io.ObjectStreamClass.getSerializableConstructor(ObjectStreamClass.java:1376)
    at java.io.ObjectStreamClass.access$1500(ObjectStreamClass.java:72)
    at java.io.ObjectStreamClass$2.run(ObjectStreamClass.java:493)
    at java.io.ObjectStreamClass$2.run(ObjectStreamClass.java:468)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.io.ObjectStreamClass.<init>(ObjectStreamClass.java:468)
    at java.io.ObjectStreamClass.lookup(ObjectStreamClass.java:365)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1133)
    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:347)
    [application code]

2016-03-10 15:04:14,640 WARN  [http-xxx:7443-16] org.apache.wicket.page.PageAccessSynchronizer: Thread 'http-xxx:7443-16' failed to acquire lock to page with id '11', attempted for 3 minutes out of allowed 3 minutes. The thread that holds the lock has name 'http-xxx:7443-38'.
2016-03-10 15:04:14,642 WARN  [http-xxx:7443-16] org.apache.wicket.page.PageAccessSynchronizer: "http-xxx:7443-38" daemon prio=5 tid=9088 state=RUNNABLE 
org.apache.wicket.util.lang.Threads$ThreadDump
    at java.lang.Class.getDeclaredConstructors0(Native Method)
    at java.lang.Class.privateGetDeclaredConstructors(Class.java:2595)
    at java.lang.Class.getConstructor0(Class.java:2895)
    at java.lang.Class.newInstance(Class.java:354)
    at sun.reflect.MethodAccessorGenerator$1.run(MethodAccessorGenerator.java:399)
    at sun.reflect.MethodAccessorGenerator$1.run(MethodAccessorGenerator.java:396)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.reflect.MethodAccessorGenerator.generate(MethodAccessorGenerator.java:395)
    at sun.reflect.MethodAccessorGenerator.generateMethod(MethodAccessorGenerator.java:77)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:46)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606) 
    [application code]

我们目前无法重现这一点(仍在努力).但也许社区中的某些人已经看到了类似的东西,并且知道什么可以帮助我们重现或解决问题.我们目前的一个猜测是,这与本机内存消耗有关(由于http://www.ibm.com/developerworks/java/library/j-nativememory-linux/等信息)但我们没有看到任何在日志中提示这方面的问题(没有OutOfMemory错误,没有来自linux管理员的报告,系统内存不足)

Answer 1

我们从未能够妥善解决这个问题，但在某个时候它就消失了。如果我没记错的话，客户端更改了 appdynamics 配置/删除了它，这似乎已经解决了问题。