Java 阻塞问题：为什么 JVM 会阻塞许多不同类/方法中的线程？

发布于 2024-09-28 19:14:10 字数 2737 浏览 7 评论 0原文

更新：这看起来像是内存问题。 3.8 Gb Hprof 文件表明，发生此“阻塞”时 JVM 正在转储堆。我们的运营团队发现该站点没有响应，进行了堆栈跟踪，然后关闭了该实例。我相信他们在堆转储完成之前关闭了该网站。日志没有错误/异常/问题证据——可能是因为 JVM 在生成错误消息之前就被终止了。

原始问题我们最近遇到过这样的情况：对于最终用户来说，应用程序似乎挂起。我们在应用程序重新启动之前获得了堆栈跟踪，我发现了一些令人惊讶的结果：在 527 个线程中，463 个线程状态为 BLOCKED。

过去过去阻塞线程通常有这样的问题： 1）一些明显的瓶颈：例如某些数据库记录锁或文件系统锁问题导致其他线程等待。 2) 所有被阻塞的线程都会阻塞在同一个类/方法上（例如 jdbc 或文件系统类）

异常数据 在这种情况下，我看到各种类/方法被阻止，包括jvm内部类，jboss类，log4j等，除了应用程序类（包括jdbc和lucene调用）

问题什么会导致 JVM 阻塞 log4j.Hierarchy.getLogger、java.lang.reflect.Constructor.newInstance？显然有些资源“稀缺”，但哪种资源呢？

谢谢

堆栈跟踪摘录

http-0.0.0.0-80-417" daemon prio=6 tid=0x000000000f6f1800 nid=0x1a00 waiting for monitor entry [0x000000002dd5d000]
   java.lang.Thread.State: BLOCKED (on object monitor)
                at sun.reflect.GeneratedConstructorAccessor68.newInstance(Unknown Source)
                at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
                at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
                at java.lang.Class.newInstance0(Class.java:355)
                at java.lang.Class.newInstance(Class.java:308)
                at org.jboss.ejb.Container.createBeanClassInstance(Container.java:630)

http-0.0.0.0-80-451" daemon prio=6 tid=0x000000000f184800 nid=0x14d4 waiting for monitor entry [0x000000003843d000]
   java.lang.Thread.State: BLOCKED (on object monitor)
                at java.lang.Class.getDeclaredMethods0(Native Method)
                at java.lang.Class.privateGetDeclaredMethods(Class.java:2427)
                at java.lang.Class.getMethod0(Class.java:2670)

"http-0.0.0.0-80-449" daemon prio=6 tid=0x000000000f17d000 nid=0x2240 waiting for monitor entry [0x000000002fa5f000]
   java.lang.Thread.State: BLOCKED (on object monitor)
                at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.register(Http11Protocol.java:638)
                - waiting to lock <0x00000007067515e8> (a org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler)
                at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.createProcessor(Http11Protocol.java:630)


"http-0.0.0.0-80-439" daemon prio=6 tid=0x000000000f701800 nid=0x1ed8 waiting for monitor entry [0x000000002f35b000]
   java.lang.Thread.State: BLOCKED (on object monitor)
                at org.apache.log4j.Hierarchy.getLogger(Hierarchy.java:261)
                at org.apache.log4j.Hierarchy.getLogger(Hierarchy.java:242)
                at org.apache.log4j.LogManager.getLogger(LogManager.java:198)

原文

Update: This looks like a memory issue. A 3.8 Gb Hprof file indicated that the JVM was dumping-its-heap when this "blocking" occurred. Our operations team saw that the site wasn't responding, took a stack trace, then shut down the instance. I believe they shut down the site before the heap dump finished. The log had no errors/exceptions/evidence of problems--probably because the JVM was killed before it could generate an error message.

Original Question
We had a recent situation where the application appeared --to the end user--to hang. We got a stack trace before the application restart and I found some surprising results: of 527 threads, 463 had thread state BLOCKED.

In the Past
In the past blocked thread usually had this issue:
1) some obvious bottleneck: e.g. some database record lock or file system lock problem which caused other threads to wait.
2) All blocked threads would block on the same class/method (e.g. the jdbc or file system clases)

Unusual Data
In this case, I see all sorts of classes/methods blocked, including jvm internal classes, jboss classes, log4j, etc, in addition to application classes (including jdbc and lucene calls)

The question
what would cause a JVM to block log4j.Hierarchy.getLogger, java.lang.reflect.Constructor.newInstance? Obviously some resource "is scarce" but which resource?

thanks

will

Stack Trace Excerpts

http-0.0.0.0-80-417" daemon prio=6 tid=0x000000000f6f1800 nid=0x1a00 waiting for monitor entry [0x000000002dd5d000]
   java.lang.Thread.State: BLOCKED (on object monitor)
                at sun.reflect.GeneratedConstructorAccessor68.newInstance(Unknown Source)
                at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
                at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
                at java.lang.Class.newInstance0(Class.java:355)
                at java.lang.Class.newInstance(Class.java:308)
                at org.jboss.ejb.Container.createBeanClassInstance(Container.java:630)

http-0.0.0.0-80-451" daemon prio=6 tid=0x000000000f184800 nid=0x14d4 waiting for monitor entry [0x000000003843d000]
   java.lang.Thread.State: BLOCKED (on object monitor)
                at java.lang.Class.getDeclaredMethods0(Native Method)
                at java.lang.Class.privateGetDeclaredMethods(Class.java:2427)
                at java.lang.Class.getMethod0(Class.java:2670)

"http-0.0.0.0-80-449" daemon prio=6 tid=0x000000000f17d000 nid=0x2240 waiting for monitor entry [0x000000002fa5f000]
   java.lang.Thread.State: BLOCKED (on object monitor)
                at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.register(Http11Protocol.java:638)
                - waiting to lock <0x00000007067515e8> (a org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler)
                at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.createProcessor(Http11Protocol.java:630)


"http-0.0.0.0-80-439" daemon prio=6 tid=0x000000000f701800 nid=0x1ed8 waiting for monitor entry [0x000000002f35b000]
   java.lang.Thread.State: BLOCKED (on object monitor)
                at org.apache.log4j.Hierarchy.getLogger(Hierarchy.java:261)
                at org.apache.log4j.Hierarchy.getLogger(Hierarchy.java:242)
                at org.apache.log4j.LogManager.getLogger(LogManager.java:198)

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云归处 2024-10-05 19:14:10

这些大致按照我尝试的顺序列出，具体取决于收集的证据：

您看过GC 行为吗？你有记忆压力吗？这可能会导致 newInstance() 和上面的其他一些被阻止。使用 -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -verbose:gc 运行虚拟机并记录输出。您是否在接近故障/锁定时间时看到过多的 GC 时间？
- 该条件可重复吗？如果是这样，请尝试在 JVM (-Xmx) 中改变堆大小，并查看行为是否发生显着变化。如果是这样，请查找内存泄漏或为您的应用适当调整堆大小。
- 如果前面的方法很困难，并且您在应该出现 OutOfMemoryError 的情况下却没有出现，您可以调整 GC 可调参数...请参阅 JDK6.0 XX 选项，或 JDK6.0 GC 调优白皮书。具体查看 -XX:+UseGCOverheadLimit 和 -XX:+GCTimeLimit 以及相关选项。（请注意，这些没有详细记录，但可能有用......）
可能会出现死锁吗？仅凭堆栈跟踪摘录，无法在此处确定。查找线程被阻塞的监视器状态之间的循环（相对于它们所持有的内容）。我相信 jconsole 可以为您做到这一点......（
尝试执行几次重复堆栈跟踪并查找哪些变化与哪些保持不变...
进行取证...对于每个显示“BLOCKED”的堆栈条目，查找特定的代码行并确定那里是否有监视器。如果有实际的监视器获取，那么识别限制资源应该相当容易。但是，如果没有透明可用的监视器，您的某些线程可能会显示为阻塞，这将更加棘手......