| [备忘]druid公平锁导致的程序卡顿 | ||
| 添加日期：2023/12/31 8:54:53 | 快速返回 返回列表 | 阅读245次 |
日志中找到堆栈dump， 发现大量请求在等待数据库连接。 "http-apr-7001-exec-146" Id=4693 TIMED_WAITING on java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject@5727538a at sun.misc.Unsafe.park(Native Method) - waiting on java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject@5727538a at java.util.concurrent.locks.LockSupport.parkNanos(Unknown Source) at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(Unknown Source) at com.alibaba.druid.pool.DruidDataSource.pollLast(DruidDataSource.java:1568) at com.alibaba.druid.pool.DruidDataSource.getConnectionInternal(DruidDataSource.java:1144) at com.alibaba.druid.pool.DruidDataSource.getConnectionDirect(DruidDataSource.java:1017) 数据库配置的100连接，看来用光了。 然后发现一些线程卡在归还connection上 "http-apr-7001-exec-249" Id=4797 WAITING on java.util.concurrent.locks.ReentrantLock$FairSync@43f6891 at sun.misc.Unsafe.park(Native Method) - waiting on java.util.concurrent.locks.ReentrantLock$FairSync@43f6891 at java.util.concurrent.locks.LockSupport.park(Unknown Source) at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(Unknown Source) at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireInterruptibly(Unknown Source) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(Unknown Source) at java.util.concurrent.locks.ReentrantLock.lockInterruptibly(Unknown Source) at com.alibaba.druid.pool.DruidDataSource.recycle(DruidDataSource.java:1338) at com.alibaba.druid.pool.DruidPooledConnection.recycle(DruidPooledConnection.java:305) at com.alibaba.druid.filter.FilterChainImpl.dataSource_recycle(FilterChainImpl.java:4534) at com.alibaba.druid.filter.stat.StatFilter.dataSource_releaseConnection(StatFilter.java:647) at com.alibaba.druid.filter.FilterChainImpl.dataSource_recycle(FilterChainImpl.java:4530) at com.alibaba.druid.pool.DruidPooledConnection.close(DruidPooledConnection.java:253) at org.springframework.jdbc.datasource.DataSourceUtils.doCloseConnection(DataSourceUtils.java:341) at org.springframework.jdbc.datasource.DataSourceUtils.doReleaseConnection(DataSourceUtils.java:328) 一些卡在获取connection上 "http-apr-7001-exec-204" Id=4752 WAITING on java.util.concurrent.locks.ReentrantLock$FairSync@43f6891 at sun.misc.Unsafe.park(Native Method) - waiting on java.util.concurrent.locks.ReentrantLock$FairSync@43f6891 at java.util.concurrent.locks.LockSupport.park(Unknown Source) at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(Unknown Source) at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireInterruptibly(Unknown Source) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireInterruptibly(Unknown Source) at java.util.concurrent.locks.ReentrantLock.lockInterruptibly(Unknown Source) at com.alibaba.druid.pool.DruidDataSource.getConnectionInternal(DruidDataSource.java:1126) at com.alibaba.druid.pool.DruidDataSource.getConnectionDirect(DruidDataSource.java:1017) at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4544) at com.alibaba.druid.filter.stat.StatFilter.dataSource_getConnection(StatFilter.java:662) at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4540) at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:995) 注意，它们在竞争公平锁。java.util.concurrent.locks.ReentrantLock$FairSync@43f6891 负责创建连接的线程，也在等待公平锁。 "Druid-ConnectionPool-Create-297239085" Id=15 WAITING on java.util.concurrent.locks.ReentrantLock$FairSync@43f6891 at sun.misc.Unsafe.park(Native Method) - waiting on java.util.concurrent.locks.ReentrantLock$FairSync@43f6891 at java.util.concurrent.locks.LockSupport.park(Unknown Source) at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(Unknown Source) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(Unknown Source) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(Unknown Source) at java.util.concurrent.locks.ReentrantLock$FairSync.lock(Unknown Source) at java.util.concurrent.locks.ReentrantLock.lock(Unknown Source) at com.alibaba.druid.pool.DruidDataSource.put(DruidDataSource.java:1815) at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2033) 搜了下，貌似公平锁影响性能。 大概是这样： 比如5个线程去释放连接，100个请求去获取连接，后者明显多， 公平锁，大家机会平等？然后大概率前5个得不到锁，所以释放不掉连接。哈哈。 看了下druid的源代码： public void setMaxWait(long maxWaitMillis) { if (maxWaitMillis != this.maxWait) { if (maxWaitMillis > 0L && this.useUnfairLock == null && !this.inited) { ReentrantLock lock = this.lock; lock.lock(); try { if (!this.inited && !lock.isFair()) { this.lock = new ReentrantLock(true); this.notEmpty = this.lock.newCondition(); this.empty = this.lock.newCondition(); } } finally { lock.unlock(); } } if (this.inited) { LOG.error("maxWait changed : " + this.maxWait + " -> " + maxWaitMillis); } this.maxWait = maxWaitMillis; } } setMaxWait的时候，会使用公平锁（如果没有设置useUnfairLock属性）。 public void setUseUnfairLock(boolean useUnfairLock) { if (this.lock.isFair() != !useUnfairLock) { if (!this.inited) { ReentrantLock lock = this.lock; lock.lock(); try { if (!this.inited) { this.lock = new ReentrantLock(!useUnfairLock); this.notEmpty = this.lock.newCondition(); this.empty = this.lock.newCondition(); this.useUnfairLock = useUnfairLock; } } finally { lock.unlock(); } } } } setUseUnfairLock时会使用非公平锁，并设置this.useUnfairLock属性。 所以setUseUnfairLock和setMaxWait谁先执行，无所谓，都会变成非公平锁。 我的程序里，只设置了maxWait，没写UseUnFaireLock，所以是公平锁。 那么增加UseUnFaireLock为true即可。 当然，最大连接数，还是需要改大一些。 参考文章： https://tech.youzan.com/you-zan-shu-ju-ku-lian-jie-chi-xing-neng-you-hua/ https://blog.csdn.net/beFocused/article/details/108533137 |
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