最近在IDEA中启动Tomcat经常会碰到这个错误，起初、一直没在意，现在碰到的次数多了，就去查看下这个问题，现描述如下：
=2018-01-08 14:27:30,216 WARN [com.mchange.v2.async.ThreadPoolAsynchronousRunner] - com[email protected]29165a67 -- APPARENT DEADLOCK!!! Complete Status: Managed Threads: 3 Active Threads: 3 Active Tasks: [email protected]96 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0) [email protected]d5 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1) [email protected]63 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2) Pending Tasks: [email protected]32 [email protected]14 [email protected]6e [email protected]20 [email protected]bb [email protected]dd [email protected]c8 Pool thread stack traces: Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0,5,RMI Runtime] java.net.PlainSocketImpl.socketConnect(Native Method) java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351) java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213) java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200) java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366) java.net.Socket.connect(Socket.java:529) java.net.Socket.connect(Socket.java:478) java.net.Socket.<init>(Socket.java:375) java.net.Socket.<init>(Socket.java:189) oracle.net.nt.TcpNTAdapter.connect(Unknown Source) oracle.net.nt.ConnOption.connect(Unknown Source) oracle.net.nt.ConnStrategy.execute(Unknown Source) oracle.net.resolver.AddrResolution.resolveAndExecute(Unknown Source) oracle.net.ns.NSProtocol.establishConnection(Unknown Source) oracle.net.ns.NSProtocol.connect(Unknown Source) oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:844) oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:268) oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:420) oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:165) oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:35) oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:801) com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137) com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014) com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810) com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547) Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1,5,RMI Runtime] java.net.PlainSocketImpl.socketConnect(Native Method) java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351) java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213) java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200) java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366) java.net.Socket.connect(Socket.java:529) java.net.Socket.connect(Socket.java:478) java.net.Socket.<init>(Socket.java:375) java.net.Socket.<init>(Socket.java:189) oracle.net.nt.TcpNTAdapter.connect(Unknown Source) oracle.net.nt.ConnOption.connect(Unknown Source) oracle.net.nt.ConnStrategy.execute(Unknown Source) oracle.net.resolver.AddrResolution.resolveAndExecute(Unknown Source) oracle.net.ns.NSProtocol.establishConnection(Unknown Source) oracle.net.ns.NSProtocol.connect(Unknown Source) oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:844) oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:268) oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:420) oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:165) oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:35) oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:801) com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137) com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014) com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810) com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547) Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2,5,RMI Runtime] java.net.PlainSocketImpl.socketConnect(Native Method) java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351) java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213) java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200) java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366) java.net.Socket.connect(Socket.java:529) java.net.Socket.connect(Socket.java:478) java.net.Socket.<init>(Socket.java:375) java.net.Socket.<init>(Socket.java:189) oracle.net.nt.TcpNTAdapter.connect(Unknown Source) oracle.net.nt.ConnOption.connect(Unknown Source) oracle.net.nt.ConnStrategy.execute(Unknown Source) oracle.net.resolver.AddrResolution.resolveAndExecute(Unknown Source) oracle.net.ns.NSProtocol.establishConnection(Unknown Source) oracle.net.ns.NSProtocol.connect(Unknown Source) oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:844) oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:268) oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:420) oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:165) oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:35) oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:801) com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134) com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182) com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171) com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137) com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014) com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32) com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810) com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
在一番求知的过程中，大概了解到这个问题出现的几种可能情况，随记录下来，以供后人鉴赏：
1.数据库服务没有启动
大千世界无奇不有，这种错也有人遇到的话，真不想说什么了；如果是故意测试的话呢，个人感觉还是没有必要的，毕竟不开启数据库服务就去连接数据库，你让人作何感想啊。
2.没有创建对应数据库
这个问题同上，访问不到数据库，都不是技术性的问题，在此、不多啰嗦。
3.就涉及到c3p0连接池的配置文件了
这个问题就比较偏重于技术层面了，相关解决方案介绍如下：
①maxStatements 和checkoutTimeout
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。如果maxStatements与maxStatementsPerConnection均为0，则缓存被关闭。Default: 0。
通过上面的描述，解决方案：
<property name="maxStatements" value="0"/>
<property name="checkoutTimeout" value="100"/>
②maxPoolSize和initialPoolSize
关于这方面，我大概能够了解到我个人的问题是由于这个原因导致的。由于数据库的连接数是有限的，每有应用启动C3p0都会占用数据库的连接来填充C3p0的连接池，而当数据库的资源被占光时就会因为无法获得共享资源而报死锁。
③更新c3p0的包
至于c3p0的包版本过旧造成的，这大概是历史遗留的问题。低版本c3p0包会导致获取连接的时间过长而在获取新的连接时造成死锁，具体请参考stackoverflow中别人提出的一个问题
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The tasks that are dealocking are Connection acquisition tasks. That is, c3p0 is trying to acquire new Connections from your database, and those Connection acquisition attempts are taking a long time. The first thing I would do is upgrade to 0.9.2.1, which has a much improved means of performing a round of Connection acquisitions in situations where acquisition attempts sometimes fail. If that doesn‘t solve your problem, then you‘ll need to figure out why c3p0‘s attempts to acquire a Connection are hanging for long periods of time: neither succeeding nor failing with an Exception. |