聊聊druid的源码的几个疑问
序
本文主要聊一聊druid源码的几个疑问
asyncCloseConnectionEnable
druid-1.2.11-sources.jar!/com/alibaba/druid/pool/DruidPooledConnection.java
public void close() throws SQLException {
if (this.disable) {
return;
}
DruidConnectionHolder holder = this.holder;
if (holder == null) {
if (dupCloseLogEnable) {
LOG.error("dup close");
}
return;
}
DruidAbstractDataSource dataSource = holder.getDataSource();
boolean isSameThread = this.getOwnerThread() == Thread.currentThread();
if (!isSameThread) {
dataSource.setAsyncCloseConnectionEnable(true);
}
if (dataSource.isAsyncCloseConnectionEnable()) {
syncClose();
return;
}
//......
}
DruidPooledConnection的close方法会判断dataSource.isAsyncCloseConnectionEnable()，但是奇怪的是为true的话，执行的却是syncClose方法
numTestsPerEvictionRun
druid-1.2.11-sources.jar!/com/alibaba/druid/pool/DruidAbstractDataSource.java
protected volatile int numTestsPerEvictionRun = DEFAULT_NUM_TESTS_PER_EVICTION_RUN;
public static final int DEFAULT_NUM_TESTS_PER_EVICTION_RUN = 3;
public int getNumTestsPerEvictionRun() {
return numTestsPerEvictionRun;
}
/**
* @param numTestsPerEvictionRun
*/
@Deprecated
public void setNumTestsPerEvictionRun(int numTestsPerEvictionRun) {
this.numTestsPerEvictionRun = numTestsPerEvictionRun;
}
DruidAbstractDataSource定义了numTestsPerEvictionRun属性，不过看set方法标记为废弃了，搜了一下代码，实际没有使用到
timeBetweenEvictionRunsMillis
druid-1.2.11-sources.jar!/com/alibaba/druid/pool/DruidAbstractDataSource.java
protected volatile long timeBetweenEvictionRunsMillis = DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS;
public static final long DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS = 60 * 1000L;
DruidAbstractDataSource定义了timeBetweenEvictionRunsMillis，但是这个却是在getConnectionDirect的时候使用
druid-1.2.11-sources.jar!/com/alibaba/druid/pool/DruidDataSource.java
public DruidPooledConnection getConnectionDirect(long maxWaitMillis) throws SQLException {
for (; ; ) {
// get connection
if (testOnBorrow) {
// testConnectionInternal
} else {
if (testWhileIdle) {
long idleMillis = currentTimeMillis - lastActiveTimeMillis;
long timeBetweenEvictionRunsMillis = this.timeBetweenEvictionRunsMillis;
if (timeBetweenEvictionRunsMillis <= 0) {
timeBetweenEvictionRunsMillis = DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS;
}
if (idleMillis >= timeBetweenEvictionRunsMillis
|| idleMillis < 0 // unexcepted branch
) {
boolean validate = testConnectionInternal(poolableConnection.holder, poolableConnection.conn);
if (!validate) {
if (LOG.isDebugEnabled()) {
LOG.debug("skip not validate connection.");
}
discardConnection(poolableConnection.holder);
continue;
}
}
}
}
//......
}
}
这里用idleMillis去跟timeBetweenEvictionRunsMillis比较，似乎timeBetweenEvictionRunsMillis变量的命名不符合语义，不过它真正的用途是在DestroyConnectionThread里头，在那里才符合它命名的语义
小结
整体代码看下来感觉跟commons-pool相比，druid代码的实现感觉有点粗糙，抽象层级不够高，代码充斥大量统计标记、状态位的处理，维护起来得很小心。另外还有如下几个：
- DruidPooledConnection的close方法会判断dataSource.isAsyncCloseConnectionEnable()，但是奇怪的是为true的话，执行的却是syncClose方法
- DruidAbstractDataSource定义了numTestsPerEvictionRun属性，不过看set方法标记为废弃了，搜了一下代码，实际没有使用到
- DruidAbstractDataSource定义了timeBetweenEvictionRunsMillis，但是这个却是在getConnectionDirect的时候使用，用idleMillis去跟timeBetweenEvictionRunsMillis比较，似乎timeBetweenEvictionRunsMillis变量的命名不符合语义，不过它真正的用途是在DestroyConnectionThread里头，在那里才符合它命名的语义
- DruidDataSource配置属性列表这里的信息已经过时了也没有纠正过来，比如testOnBorrow现在默认是false
- 虽然提供了stat页面，但是微服务之后，这项功能基本也没啥用了，一般需要通过metrics集成起来
doc
- 定时连接有效性检查的支持 #1281