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我们正在使用 Hibernate 和 c3p0 连接池库。到目前为止，这种组合效果很好，直到最近我们决定将 maxPoolSize 增加到 1000 并对我们的应用程序进行大量压力测试。我们应用程序的峰值负载导致数据库响应非常缓慢，因此 c3p0 的死锁检测器一次又一次地发出明显的死锁警告。

根据 c3p0 文档，我们将 maxAdministrativeTaskTime 更改为 10 分钟，假设死锁检测每 30 分钟发生一次（代码表明死锁检测频率是 maxAdministrativeTaskTime 的三倍）。

然而，根据 c3p0 日志的分析，死锁检测线程的运行频率超过了 30 分钟。日志的相关部分附后。令人惊讶的是，频率并不统一。

Line 573745: [Timer-2] 2013-06-26 04:47:52,492 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
Line 573746: [Timer-2] 2013-06-26 04:47:52,512 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Complete Status: 
Line 574292: [Timer-2] 2013-06-26 04:49:12,493 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
Line 574293: [Timer-2] 2013-06-26 04:49:12,513 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Complete Status: 
Line 575004: [Timer-2] 2013-06-26 04:50:32,494 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
Line 575005: [Timer-2] 2013-06-26 04:50:32,511 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Complete Status: 
Line 576062: [Timer-2] 2013-06-26 04:51:52,495 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
Line 576063: [Timer-2] 2013-06-26 04:51:52,536 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Complete Status: 
Line 576720: [Timer-2] 2013-06-26 04:53:12,496 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
Line 576721: [Timer-2] 2013-06-26 04:53:12,516 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Complete Status: 
Line 594087: [Timer-2] 2013-06-26 04:55:52,550 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
Line 594088: [Timer-2] 2013-06-26 04:55:52,569 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Complete Status: 
Line 594753: [Timer-2] 2013-06-26 04:57:12,550 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
Line 594754: [Timer-2] 2013-06-26 04:57:12,572 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Complete Status: 
Line 595624: [Timer-2] 2013-06-26 04:58:32,552 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
Line 595625: [Timer-2] 2013-06-26 04:58:32,570 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Complete Status: 
Line 596416: [Timer-2] 2013-06-26 04:59:52,552 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
Line 596417: [Timer-2] 2013-06-26 04:59:52,572 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Complete Status: 
Line 611011: [Timer-2] 2013-06-26 05:02:22,556 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
Line 611012: [Timer-2] 2013-06-26 05:02:22,577 WARN [null] com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@662cee3b -- APPARENT DEADLOCK!!! Complete Status:

有人可以解释这个异常吗？

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2 回答 2

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maxAdministrativeTaskTime不影响线程池的死锁检测器；它只是限制在池尝试执行单个任务之前允许执行的长度interrupt()。一种（hackish！，丑陋！，不建议！）尝试避免明显死锁的方法是将其设置为 SHORT 间隔，以便慢速任务被中断而不是挂起太久以至于池决定它被卡住。请在此处查看一些讨论。

感谢提问者（通过电子邮件），我仔细检查了我自己的 %$^*&! 代码，死锁检测间隔受maxAdministrativeTaskTime. 正如问题所暗示的，它应该是 3 × maxAdministrativeTaskTime。所以谜团加深了。

值得了解死锁检测器的作用。c3p0 维护一个线程池，numHelperThreads很大。死锁检测器定期记录池中所有线程正在运行的任务，然后休眠一段时间，然后再次检查。如果没有任务完成，即活动任务与上次检查期间完全相同，则宣布死锁。c3p0 期望某个任务完成的时间间隔是 10 秒，目前无法配置。它可以是可配置的。

您可能会发布一些您看到的表观死锁的示例。c3p0 打印大量信息以帮助您了解可能挂起的内容。

这里有两个建议可以在非常重的负载下减少表观死锁：

  1. 您观察到的死锁与连接获取有关吗？如果是这样，如果您还没有，请升级到 c3p0-0.9.2.1 或最新的 0.9.5 预发行版。

  2. 您是否尝试过随着numHelperThreads负载的增加而增加？如果某些任务非常慢，c3p0 不会声明死锁，除非所有线程都被慢速任务阻塞。如果有足够多的线程来执行更灵活的任务，您将不会看到死锁。

我希望这有帮助！

于 2013-06-27T06:35:14.797 回答
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我无法解释，但是 1000 个连接是相当多的，您的 c3p0 配置是否反映了如此高的连接数？我的经验是默认设置适用于较少的连接数。我建议阅读c3po 文档，尤其是“其他数据源配置”下的部分。

于 2013-06-26T18:59:58.080 回答