c3p0数据库连接池死锁问题

项目进行压力测试的时候，运行大概1小时候，后台抛出以下异常：

1. Nov 9, 2012 1:41:59 AM com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector run
2. WARNING: com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@4b9cafa7 -- APPARENT DEADLOCK!!! Complete Status:
3. Managed Threads: 3
4. Active Threads: 3
5. Active Tasks:
6. com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@19f67d43 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2)
7. com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@599c706 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1)
8. com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@32d95dc9 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0)
9. Pending Tasks:
10. com.mchange.v2.resourcepool.BasicResourcePool$1DestroyResourceTask@5c9c5133
11. com.mchange.v2.resourcepool.BasicResourcePool$1DestroyResourceTask@1a971ac5
12. com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@365e8926
13. com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@787e39ac
14. Pool thread stack traces:
15. Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2,5,main]
16. java.lang.StringCoding.set(StringCoding.java:53)
17. java.lang.StringCoding.encode(StringCoding.java:270)
18. java.lang.String.getBytes(String.java:946)
19. com.mysql.jdbc.ConnectionImpl.configureCharsetProperties(ConnectionImpl.java:1578)
20. com.mysql.jdbc.ConnectionImpl.configureClientCharacterSet(ConnectionImpl.java:1628)
21. com.mysql.jdbc.ConnectionImpl.initializePropsFromServer(ConnectionImpl.java:3425)
22. com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2045)
23. com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:718)
24. com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)
25. sun.reflect.GeneratedConstructorAccessor35.newInstance(Unknown Source)
26. sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
27. java.lang.reflect.Constructor.newInstance(Constructor.java:513)
28. com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
29. com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
30. com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
31. com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:135)
32. com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
33. com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
34. com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)
35. com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
36. com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
37. com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
38. com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
39. Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1,5,main]
40. com.mysql.jdbc.ResultSetImpl.getInstance(ResultSetImpl.java:344)
41. com.mysql.jdbc.MysqlIO.buildResultSetWithUpdates(MysqlIO.java:2607)
42. com.mysql.jdbc.MysqlIO.readResultsForQueryOrUpdate(MysqlIO.java:2490)
43. com.mysql.jdbc.MysqlIO.readAllResults(MysqlIO.java:1746)
44. com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2135)
45. com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2536)
46. com.mysql.jdbc.ConnectionImpl.setupServerForTruncationChecks(ConnectionImpl.java:5240)
47. com.mysql.jdbc.ConnectionImpl.initializePropsFromServer(ConnectionImpl.java:3508)
48. com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2045)
49. com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:718)
50. com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)
51. sun.reflect.GeneratedConstructorAccessor35.newInstance(Unknown Source)
52. sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
53. java.lang.reflect.Constructor.newInstance(Constructor.java:513)
54. com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
55. com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
56. com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
57. com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:135)
58. com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
59. com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
60. com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)
61. com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
62. com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
63. com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
64. com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
65. Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0,5,main]
66. com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:562)

目测该问题是c3p0连接池导致的线程死锁。

这种数据库连接池线程死锁的问题发生的原因可能有很多，我将我的配置环境以及解决方法贴出来供大家参考一下：

使用环境，spring + hibernate +c3p0

配置如下：<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"

1. destroy-method="close">
2. <property name="driverClass" value="com.mysql.jdbc.Driver"/>
3. <property name="jdbcUrl" value="${db.url}?useUnicode=true&amp;characterEncoding=UTF-8"/>
4. <property name="user" value="${db.usrname}"/>
5. <property name="password" value="${db.password}"/>
6. <!--连接池中保留的最小连接数。-->
7. <property name="minPoolSize" value="5"/>
8. <!--连接池中保留的最大连接数。Default: 15 -->
9. <property name="maxPoolSize" value="500"/>
10. <!--初始化时获取的连接数，取值应在minPoolSize与maxPoolSize之间。Default: 3 -->
11. <property name="initialPoolSize" value="10"/>
12. <!--最大空闲时间,60秒内未使用则连接被丢弃。若为0则永不丢弃。Default: 0 -->
13. <property name="maxIdleTime" value="60"/>
14. <!--当连接池中的连接耗尽的时候c3p0一次同时获取的连接数。Default: 3 -->
15. <property name="acquireIncrement" value="5"/>
16. <!--JDBC的标准参数，用以控制数据源内加载的PreparedStatements数量。但由于预缓存的statements
17. 属于单个connection而不是整个连接池。所以设置这个参数需要考虑到多方面的因素。
18. 如果maxStatements与maxStatementsPerConnection均为0，则缓存被关闭。Default: 0-->
19. <property name="maxStatements" value="0"/>
20. <!--每60秒检查所有连接池中的空闲连接。Default: 0 -->
21. <property name="idleConnectionTestPeriod" value="60"/>
22. <!--定义在从数据库获取新连接失败后重复尝试的次数。Default: 30 -->
23. <property name="acquireRetryAttempts" value="30"/>
24. <!--获取连接失败将会引起所有等待连接池来获取连接的线程抛出异常。但是数据源仍有效
25. 保留，并在下次调用getConnection()的时候继续尝试获取连接。如果设为true，那么在尝试
26. 获取连接失败后该数据源将申明已断开并永久关闭。Default: false-->
27. <property name="breakAfterAcquireFailure" value="false"/>
28. <!--因性能消耗大请只在需要的时候使用它。如果设为true那么在每个connection提交的
29. 时候都将校验其有效性。建议使用idleConnectionTestPeriod或automaticTestTable
30. 等方法来提升连接测试的性能。Default: false -->
31. <property name="testConnectionOnCheckout" value="false"/>
32. </bean>

这个配置中有一些属性可能和死锁有关：maxStatements 和checkoutTimeout(我没有使用该属性)

有人说c3p0本身没有问题，导致问题是spring的原因，c3p0作为hibernate官方推荐的连接池，在性能和稳定性上都是中规中矩的。根据以前的使用经验，我判断也不是c3p0的问题。

1. <!--JDBC的标准参数，用以控制数据源内加载的PreparedStatements数量。但由于预缓存的statements
2. 属于单个connection而不是整个连接池。所以设置这个参数需要考虑到多方面的因素。
3. 如果maxStatements与maxStatementsPerConnection均为0，则缓存被关闭。Default: 0-->
4. <property name="maxStatements" value="0"/>
5. <!--连接池用完时客户调用getConnection()后等待获取连接的时间，单位：毫秒。超时后会抛出-->
6. <!--SQLEXCEPTION，如果设置0，则无限等待。Default:0-->
7. <property name="checkoutTimeout" value="100"/>

修改后，问题没有重现。

来自：http://www.cnblogs.com/zhishan/archive/2012/11/09/2761980.html