hikaripool信息_HikariPool源码（三）资源池动态伸缩「建议收藏」

Java极客  |  作者  /  铿然一叶

这是Java极客的第 54 篇原创文章

1.资源池的动态伸缩

1.为了提升资源池的性能，需要设置最小闲置资源数量，在资源池初始化时完成初始化；而当使用的资源超过最小闲置资源数，消费者释放回池中超过一定时间后要收缩到最小闲置资源数。

2.为了避免无限申请资源导致超出负载，需要设置最大资源数，池中资源不能超出最大资源数。

2.动态伸缩相关类结构

职责说明：

类

职责

HouseKeeper

实现了Runnable接口，负责池资源的动态伸缩。

ScheduledExecutorService

负责调度HouseKeeper。

ScheduledFuture

由ScheduledExecutorService调度返回，可以终止HouseKeeper的执行。

HikariPool

负责在构造器中初始化和调用以上类。

3.源码

3.1.HikariPool

// 初始化ScheduledExecutorService

this.houseKeepingExecutorService = initializeHouseKeepingExecutorService();

// 调度HouseKeeper， 延迟并周期性调度

this.houseKeeperTask = houseKeepingExecutorService.scheduleWithFixedDelay(new HouseKeeper(), 100L, housekeepingPeriodMs, MILLISECONDS);

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3.2.HouseKeeper

private final class HouseKeeper implements Runnable{

private volatile long previous = plusMillis(currentTime(), -housekeepingPeriodMs);

@Override

public void run(){

try {

// refresh values in case they changed via MBean

connectionTimeout = config.getConnectionTimeout();

validationTimeout = config.getValidationTimeout();

leakTaskFactory.updateLeakDetectionThreshold(config.getLeakDetectionThreshold());

catalog = (config.getCatalog() != null && !config.getCatalog().equals(catalog)) ? config.getCatalog() : catalog;

final long idleTimeout = config.getIdleTimeout();

final long now = currentTime();

// Detect retrograde time, allowing +128ms as per NTP spec.

if (plusMillis(now, 128) < plusMillis(previous, housekeepingPeriodMs)) {

logger.warn(“{} – Retrograde clock change detected (housekeeper delta={}), soft-evicting connections from pool.”,

poolName, elapsedDisplayString(previous, now));

previous = now;

softEvictConnections();

return;

}

else if (now > plusMillis(previous, (3 * housekeepingPeriodMs) / 2)) {

// No point evicting for forward clock motion, this merely accelerates connection retirement anyway

logger.warn(“{} – Thread starvation or clock leap detected (housekeeper delta={}).”, poolName, elapsedDisplayString(previous, now));

}

previous = now;

String afterPrefix = “Pool “;

if (idleTimeout > 0L && config.getMinimumIdle() < config.getMaximumPoolSize()) {

logPoolState(“Before cleanup “);

afterPrefix = “After cleanup “;

// 获取未使用的资源

final List notInUse = connectionBag.values(STATE_NOT_IN_USE);

// 未使用资源大于配置的最小闲置资源则关闭多余资源

int toRemove = notInUse.size() – config.getMinimumIdle();

for (PoolEntry entry : notInUse) {

if (toRemove > 0 && elapsedMillis(entry.lastAccessed, now) > idleTimeout && connectionBag.reserve(entry)) {

closeConnection(entry, “(connection has passed idleTimeout)”);

toRemove–;

}

}

}

logPoolState(afterPrefix);

// 除了动态减少资源，这里动态扩容资源

fillPool(); // Try to maintain minimum connections

}

catch (Exception e) {

logger.error(“Unexpected exception in housekeeping task”, e);

}

}

}

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动态扩容资源：

//HikariPool.java

private synchronized void fillPool(){

final int connectionsToAdd = Math.min(config.getMaximumPoolSize() – getTotalConnections(), config.getMinimumIdle() – getIdleConnections())

– addConnectionQueue.size();

for (int i = 0; i < connectionsToAdd; i++) {

addConnectionExecutor.submit((i < connectionsToAdd – 1) ? poolEntryCreator : postFillPoolEntryCreator);

}

}

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3.3.ConcurrentBag

在ConcurrentBag中释放资源时之会修改资源的状态，不会去改变资源池可用资源数量。

public void requite(final T bagEntry){

// 这里只是修改资源状态，并不减少资源池中可用资源数量。

bagEntry.setState(STATE_NOT_IN_USE);

for (int i = 0; waiters.get() > 0; i++) {

if (bagEntry.getState() != STATE_NOT_IN_USE || handoffQueue.offer(bagEntry)) {

return;

}

else if ((i & 0xff) == 0xff) { // 0xff 是255， 每隔256进去一次

parkNanos(MICROSECONDS.toNanos(10));

}

else {

yield();

}

}

final List threadLocalList = threadList.get();

if (threadLocalList.size() < 50) {

threadLocalList.add(weakThreadLocals ? new WeakReference<>(bagEntry) : bagEntry);

}

}

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4.总结

资源池在初始化时初始化最小资源数。

资源的动态伸缩可以通过JUC工具ScheduledExecutorService调度线程完成，而不需要额外使用第三方定时器。

消费者释放资源时并不会立即减少资源池可用资源数量，因为很可能其他的消费者又会申请资源，为了避免减少无谓的创建资源操作，释放的资源应该在超过一定时间后才真正关闭。

end.