当DEADLOCK被冬眠的DeadlockDetector（com.mchange.v2.async.ThreadPoolAsynchronousRunner $ DeadlockDetector）和SQL错误1205（锁定等待超时）反复识别时，c3p0的所有线程都被卡住，并且hole应用程序冻结。 /> 我对避免死锁本身的解决方案不感兴趣，但有可能以编程方式对此做出反应。
在这种情况下，其他一些应用程序在数据库服务器上产生了表锁。 在终止应用程序（SIGKILL）并重新启动之后，一切都很好。
APPARENT DEADLOCK!!! Creating emergency threads for unassigned pending tasks!
SQL Error: 1205, SQLState: 40001
Lock wait timeout exceeded; try restarting transaction
使用的版本：
c3p0：0.9.5.2
休眠状态：5.0.0.CR1
完全没有春天。
完整堆栈跟踪：
2019-04-12 15:04:27,102 [WARN ] Slf4jMLog$Slf4jMLogger$WarnLogger (C3P0PooledConnectionPoolManager[identityToken->2s35s8a24vskkqigquy5|31304f14]-AdminTaskTimer) - com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@4d710599 -- APPARENT DEADLOCK!!! Creating
emergency threads for unassigned pending tasks!
2019-04-12 15:04:27,104 [WARN ] Slf4jMLog$Slf4jMLogger$WarnLogger (C3P0PooledConnectionPoolManager[identityToken->2s35s8a24vskkqigquy5|31304f14]-AdminTaskTimer) - com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@4d710599 -- APPARENT DEADLOCK!!! Complete
Status:
Managed Threads: 3
Active Threads: 3
Active Tasks:
com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask@679ab26c
on thread: C3P0PooledConnectionPoolManager[identityToken->2s35s8a24vskkqigquy5|31304f14]-HelperThread-#2
com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask@c9f62bd
on thread: C3P0PooledConnectionPoolManager[identityToken->2s35s8a24vskkqigquy5|31304f14]-HelperThread-#0
com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask@6250fbb8
on thread: C3P0PooledConnectionPoolManager[identityToken->2s35s8a24vskkqigquy5|31304f14]-HelperThread-#1
Pending Tasks:
com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask@4cdc18cd
com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@7ee7dae8
com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@99ac503
com.mchange.v2.c3p0.stmt.GooGooStatementCache$1StmtAcquireTask@6cf272b3
com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@40c40590
com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@34b7fa
com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@5f59d822
com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@20414e90
Pool thread stack traces:
Thread[C3P0PooledConnectionPoolManager[identityToken->2s35s8a24vskkqigquy5|31304f14]-HelperThread-#2,5,main]
com.mysql.jdbc.PreparedStatement.realClose(PreparedStatement.java:2689)
com.mysql.jdbc.StatementImpl.close(StatementImpl.java:534)
com.mchange.v1.db.sql.StatementUtils.attemptClose(StatementUtils.java:53)
com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask.run(GooGooStatementCache.java:934)
com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)
Thread[C3P0PooledConnectionPoolManager[identityToken->2s35s8a24vskkqigquy5|31304f14]-HelperThread-#0,5,main]
com.mysql.jdbc.PreparedStatement.realClose(PreparedStatement.java:2689)
com.mysql.jdbc.StatementImpl.close(StatementImpl.java:534)
com.mchange.v1.db.sql.StatementUtils.attemptClose(StatementUtils.java:53)
com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask.run(GooGooStatementCache.java:934)
com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)
Thread[C3P0PooledConnectionPoolManager[identityToken->2s35s8a24vskkqigquy5|31304f14]-HelperThread-#1,5,main]
com.mysql.jdbc.PreparedStatement.realClose(PreparedStatement.java:2689)
com.mysql.jdbc.StatementImpl.close(StatementImpl.java:534)
com.mchange.v1.db.sql.StatementUtils.attemptClose(StatementUtils.java:53)
com.mchange.v2.c3p0.stmt.GooGooStatementCache$StatementDestructionManager$1UncheckedStatementCloseTask.run(GooGooStatementCache.java:934)
com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)
#tread 1
2019-04-12 15:04:28,795 [WARN ] SqlExceptionHelper (qtp1548271808-41) - SQL Error: 1205, SQLState: 40001
2019-04-12 15:04:28,797 [ERROR] SqlExceptionHelper (qtp1548271808-41) - Lock wait timeout exceeded; try restarting transaction
#tread 2
2019-04-12 15:05:18,799 [WARN ] SqlExceptionHelper (qtp1548271808-23) - SQL Error: 1205, SQLState: 40001
2019-04-12 15:05:18,800 [ERROR] SqlExceptionHelper (qtp1548271808-23) - Lock wait timeout exceeded; try restarting transaction
#tread 3
2019-04-12 15:05:18,799 [WARN ] SqlExceptionHelper (qtp1548271808-22) - SQL Error: 1205, SQLState: 40001
2019-04-12 15:05:18,801 [ERROR] SqlExceptionHelper (qtp1548271808-22) - Lock wait timeout exceeded; try restarting transaction
答案 0 :(得分：0)
从APPARENT DEADLOCK数据转储中可以明显看出，由于试图关闭冻结的冻结语句而导致了死锁。关于c3p0语句缓存与某些JDBC驱动程序（尤其是Oracle和jTDS）的交互，这是一个已知问题/脆弱性。
有两种方法可以解决此问题。最简单的一种是禁用语句缓存：确保c3p0配置参数maxStatements和maxStatementsPerConnection都设置为零。
如果您希望保留语句缓存带来的性能优势，则c3p0具有setting to work around this issue。 TL； DR：：添加c3p0配置属性c3p0.statementCacheNumDeferredCloseThreads=1