This is the first day of my participation in the Gwen Challenge in November. Check out the details: the last Gwen Challenge in 2021
Introduction to the
After exploring the key code for Alibaba Druid’s connection pool initialization and getting connections, let’s look at the initialization section in more detail
The database connection pool is initialized
Comment the entire code as follows:
public void init(a) throws SQLException {
// It has already been initialized
if (inited) {
return;
}
// bug fixed for dead lock, for issue #2980
DruidDriver.getInstance();
// Lock during initialization
final ReentrantLock lock = this.lock;
try {
lock.lockInterruptibly();
} catch (InterruptedException e) {
throw new SQLException("interrupt", e);
}
boolean init = false;
try {
if (inited) {
return;
}
initStackTrace = Utils.toString(Thread.currentThread().getStackTrace());
// This part is not clear
this.id = DruidDriver.createDataSourceId();
if (this.id > 1) {
long delta = (this.id - 1) * 100000;
this.connectionIdSeedUpdater.addAndGet(this, delta);
this.statementIdSeedUpdater.addAndGet(this, delta);
this.resultSetIdSeedUpdater.addAndGet(this, delta);
this.transactionIdSeedUpdater.addAndGet(this, delta);
}
// Database connection URL
if (this.jdbcUrl ! =null) {
this.jdbcUrl = this.jdbcUrl.trim();
initFromWrapDriverUrl();
}
// filter is associated and is currently empty
for (Filter filter : filters) {
filter.init(this);
}
// Get the database type
if (this.dbTypeName == null || this.dbTypeName.length() == 0) {
this.dbTypeName = JdbcUtils.getDbType(jdbcUrl, null);
}
Mysql, Mariadb, Oceanbase, ADS
DbType dbType = DbType.of(this.dbTypeName);
if (dbType == DbType.mysql
|| dbType == DbType.mariadb
|| dbType == DbType.oceanbase
|| dbType == DbType.ads) {
boolean cacheServerConfigurationSet = false;
if (this.connectProperties.containsKey("cacheServerConfiguration")) {
cacheServerConfigurationSet = true;
} else if (this.jdbcUrl.indexOf("cacheServerConfiguration") != -1) {
cacheServerConfigurationSet = true;
}
if (cacheServerConfigurationSet) {
this.connectProperties.put("cacheServerConfiguration"."true"); }}// Here are some examples of the configuration
// Would it be better to put this part first?
if (maxActive <= 0) {
throw new IllegalArgumentException("illegal maxActive " + maxActive);
}
if (maxActive < minIdle) {
throw new IllegalArgumentException("illegal maxActive " + maxActive);
}
if (getInitialSize() > maxActive) {
throw new IllegalArgumentException("illegal initialSize " + this.initialSize + ", maxActive " + maxActive);
}
if (timeBetweenLogStatsMillis > 0 && useGlobalDataSourceStat) {
throw new IllegalArgumentException("timeBetweenLogStatsMillis not support useGlobalDataSourceStat=true");
}
if (maxEvictableIdleTimeMillis < minEvictableIdleTimeMillis) {
throw new SQLException("maxEvictableIdleTimeMillis must be grater than minEvictableIdleTimeMillis");
}
if (keepAlive && keepAliveBetweenTimeMillis <= timeBetweenEvictionRunsMillis) {
throw new SQLException("keepAliveBetweenTimeMillis must be grater than timeBetweenEvictionRunsMillis");
}
/ / driverClass related
if (this.driverClass ! =null) {
this.driverClass = driverClass.trim();
}
// This section has some initial loading and checking, but it is not very clear
initFromSPIServiceLoader();
resolveDriver();
initCheck();
initExceptionSorter();
initValidConnectionChecker();
validationQueryCheck();
// It is not clear what Stat does
if (isUseGlobalDataSourceStat()) {
dataSourceStat = JdbcDataSourceStat.getGlobal();
if (dataSourceStat == null) {
dataSourceStat = new JdbcDataSourceStat("Global"."Global".this.dbTypeName);
JdbcDataSourceStat.setGlobal(dataSourceStat);
}
if (dataSourceStat.getDbType() == null) {
dataSourceStat.setDbType(this.dbTypeName); }}else {
dataSourceStat = new JdbcDataSourceStat(this.name, this.jdbcUrl, this.dbTypeName, this.connectProperties);
}
dataSourceStat.setResetStatEnable(this.resetStatEnable);
// Key database connection pool-related, which is obtained from DruidConnectionHolder in connection obtaining
connections = new DruidConnectionHolder[maxActive];
evictConnections = new DruidConnectionHolder[maxActive];
keepAliveConnections = new DruidConnectionHolder[maxActive];
SQLException connectError = null;
// Create a database physical connection asynchronously
DruidConnectionHolder = DruidConnectionHolder = DruidConnectionHolder = DruidConnectionHolder
if(createScheduler ! =null && asyncInit) {
for (int i = 0; i < initialSize; ++i) {
submitCreateTask(true); }}else if(! asyncInit) {// init connections
while (poolingCount < initialSize) {
try {
PhysicalConnectionInfo pyConnectInfo = createPhysicalConnection();
DruidConnectionHolder holder = new DruidConnectionHolder(this, pyConnectInfo);
connections[poolingCount++] = holder;
} catch (SQLException ex) {
LOG.error("init datasource error, url: " + this.getUrl(), ex);
if (initExceptionThrow) {
connectError = ex;
break;
} else {
Thread.sleep(3000); }}}if (poolingCount > 0) { poolingPeak = poolingCount; poolingPeakTime = System.currentTimeMillis(); }}// Some auxiliary initialization operations such as logging
createAndLogThread();
createAndStartCreatorThread();
createAndStartDestroyThread();
initedLatch.await();
init = true;
initedTime = new Date();
registerMbean();
if(connectError ! =null && poolingCount == 0) {
throw connectError;
}
// initialSize is the initial number of connections
// This is keepAlive
if (keepAlive) {
// async fill to minIdle
if(createScheduler ! =null) {
for (int i = 0; i < minIdle; ++i) {
submitCreateTask(true); }}else {
this.emptySignal(); }}}catch (SQLException e) {
LOG.error("{dataSource-" + this.getID() + "} init error", e);
throw e;
} catch (InterruptedException e) {
throw new SQLException(e.getMessage(), e);
} catch (RuntimeException e){
LOG.error("{dataSource-" + this.getID() + "} init error", e);
throw e;
} catch (Error e){
LOG.error("{dataSource-" + this.getID() + "} init error", e);
throw e;
} finally {
inited = true;
lock.unlock();
if (init && LOG.isInfoEnabled()) {
String msg = "{dataSource-" + this.getID();
if (this.name ! =null&&!this.name.isEmpty()) {
msg += ",";
msg += this.name;
}
msg += "} inited"; LOG.info(msg); }}}Copy the codeconclusion
As can be seen from above:
- Initializing a double-checked lock
- The database can generate the configured initial number of connections asynchronously or synchronously
- If keepalive is true, the configured minimum number of idle connections is generated asynchronously
I only have a brief understanding of the entire initialization process, but there are so many details that I feel I don’t understand the business scenario well enough