https://github.com/brettwooldridge/HikariCP: Ultimate JDBC Connection Pool (Zaxxer.com)
  • Brett Wooldridge 
/*
 * Copyright (C) 2013,2014 Brett Wooldridge
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.zaxxer.hikari.pool;

import com.codahale.metrics.MetricRegistry;
import com.codahale.metrics.health.HealthCheckRegistry;
import com.zaxxer.hikari.HikariConfig;
import com.zaxxer.hikari.HikariPoolMXBean;
import com.zaxxer.hikari.metrics.MetricsTrackerFactory;
import com.zaxxer.hikari.metrics.PoolStats;
import com.zaxxer.hikari.metrics.dropwizard.CodahaleHealthChecker;
import com.zaxxer.hikari.metrics.dropwizard.CodahaleMetricsTrackerFactory;
import com.zaxxer.hikari.metrics.micrometer.MicrometerMetricsTrackerFactory;
import com.zaxxer.hikari.util.ConcurrentBag;
import com.zaxxer.hikari.util.ConcurrentBag.IBagStateListener;
import com.zaxxer.hikari.util.SuspendResumeLock;
import com.zaxxer.hikari.util.UtilityElf.DefaultThreadFactory;
import io.micrometer.core.instrument.MeterRegistry;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.SQLTransientConnectionException;
import java.util.Collection;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.ThreadPoolExecutor;

import static com.zaxxer.hikari.util.ClockSource.currentTime;
import static com.zaxxer.hikari.util.ClockSource.elapsedDisplayString;
import static com.zaxxer.hikari.util.ClockSource.elapsedMillis;
import static com.zaxxer.hikari.util.ClockSource.plusMillis;
import static com.zaxxer.hikari.util.ConcurrentBag.IConcurrentBagEntry.STATE_IN_USE;
import static com.zaxxer.hikari.util.ConcurrentBag.IConcurrentBagEntry.STATE_NOT_IN_USE;
import static com.zaxxer.hikari.util.UtilityElf.createThreadPoolExecutor;
import static com.zaxxer.hikari.util.UtilityElf.quietlySleep;
import static com.zaxxer.hikari.util.UtilityElf.safeIsAssignableFrom;
import static java.util.Collections.unmodifiableCollection;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static java.util.concurrent.TimeUnit.SECONDS;


This is the primary connection pool class that provides the basic
pooling behavior for HikariCP.

Author:Brett Wooldridge
/**
 * This is the primary connection pool class that provides the basic
 * pooling behavior for HikariCP.
 *
 * @author Brett Wooldridge
 */
public final class HikariPool extends PoolBase implements HikariPoolMXBean, IBagStateListener
{
   private final Logger logger = LoggerFactory.getLogger(HikariPool.class);

   public static final int POOL_NORMAL = 0;
   public static final int POOL_SUSPENDED = 1;
   public static final int POOL_SHUTDOWN = 2;

   public volatile int poolState;

   private final long aliveBypassWindowMs = Long.getLong("com.zaxxer.hikari.aliveBypassWindowMs", MILLISECONDS.toMillis(500));
   private final long housekeepingPeriodMs = Long.getLong("com.zaxxer.hikari.housekeeping.periodMs", SECONDS.toMillis(30));

   private static final String EVICTED_CONNECTION_MESSAGE = "(connection was evicted)";
   private static final String DEAD_CONNECTION_MESSAGE = "(connection is dead)";

   private final PoolEntryCreator poolEntryCreator = new PoolEntryCreator(null /*logging prefix*/);
   private final PoolEntryCreator postFillPoolEntryCreator = new PoolEntryCreator("After adding ");
   private final Collection<Runnable> addConnectionQueue;
   private final ThreadPoolExecutor addConnectionExecutor;
   private final ThreadPoolExecutor closeConnectionExecutor;

   private final ConcurrentBag<PoolEntry> connectionBag;

   private final ProxyLeakTaskFactory leakTaskFactory;
   private final SuspendResumeLock suspendResumeLock;

   private final ScheduledExecutorService houseKeepingExecutorService;
   private ScheduledFuture<?> houseKeeperTask;

   
Construct a HikariPool with the specified configuration.

Params:
  • config – a HikariConfig instance
/**
    * Construct a HikariPool with the specified configuration.
    *
    * @param config a HikariConfig instance
    */
   public HikariPool(final HikariConfig config)
   {
      super(config);

      this.connectionBag = new ConcurrentBag<>(this);
      this.suspendResumeLock = config.isAllowPoolSuspension() ? new SuspendResumeLock() : SuspendResumeLock.FAUX_LOCK;

      this.houseKeepingExecutorService = initializeHouseKeepingExecutorService();

      checkFailFast();

      if (config.getMetricsTrackerFactory() != null) {
         setMetricsTrackerFactory(config.getMetricsTrackerFactory());
      }
      else {
         setMetricRegistry(config.getMetricRegistry());
      }

      setHealthCheckRegistry(config.getHealthCheckRegistry());

      handleMBeans(this, true);

      ThreadFactory threadFactory = config.getThreadFactory();

      LinkedBlockingQueue<Runnable> addQueue = new LinkedBlockingQueue<>(config.getMaximumPoolSize());
      this.addConnectionQueue = unmodifiableCollection(addQueue);
      this.addConnectionExecutor = createThreadPoolExecutor(addQueue, poolName + " connection adder", threadFactory, new ThreadPoolExecutor.DiscardPolicy());
      this.closeConnectionExecutor = createThreadPoolExecutor(config.getMaximumPoolSize(), poolName + " connection closer", threadFactory, new ThreadPoolExecutor.CallerRunsPolicy());

      this.leakTaskFactory = new ProxyLeakTaskFactory(config.getLeakDetectionThreshold(), houseKeepingExecutorService);

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

      if (Boolean.getBoolean("com.zaxxer.hikari.blockUntilFilled") && config.getInitializationFailTimeout() > 1) {
         addConnectionExecutor.setCorePoolSize(Runtime.getRuntime().availableProcessors());
         addConnectionExecutor.setMaximumPoolSize(Runtime.getRuntime().availableProcessors());

         final long startTime = currentTime();
         while (elapsedMillis(startTime) < config.getInitializationFailTimeout() && getTotalConnections() < config.getMinimumIdle()) {
            quietlySleep(MILLISECONDS.toMillis(100));
         }

         addConnectionExecutor.setCorePoolSize(1);
         addConnectionExecutor.setMaximumPoolSize(1);
      }
   }

   
Get a connection from the pool, or timeout after connectionTimeout milliseconds.

Throws:
  • SQLException – thrown if a timeout occurs trying to obtain a connection
Returns:a java.sql.Connection instance
/**
    * Get a connection from the pool, or timeout after connectionTimeout milliseconds.
    *
    * @return a java.sql.Connection instance
    * @throws SQLException thrown if a timeout occurs trying to obtain a connection
    */
   public Connection getConnection() throws SQLException
   {
      return getConnection(connectionTimeout);
   }

   
Get a connection from the pool, or timeout after the specified number of milliseconds.

Params:
  • hardTimeout – the maximum time to wait for a connection from the pool
Throws:
  • SQLException – thrown if a timeout occurs trying to obtain a connection
Returns:a java.sql.Connection instance
/**
    * Get a connection from the pool, or timeout after the specified number of milliseconds.
    *
    * @param hardTimeout the maximum time to wait for a connection from the pool
    * @return a java.sql.Connection instance
    * @throws SQLException thrown if a timeout occurs trying to obtain a connection
    */
   public Connection getConnection(final long hardTimeout) throws SQLException
   {
      suspendResumeLock.acquire();
      final long startTime = currentTime();

      try {
         long timeout = hardTimeout;
         do {
            PoolEntry poolEntry = connectionBag.borrow(timeout, MILLISECONDS);
            if (poolEntry == null) {
               break; // We timed out... break and throw exception
            }

            final long now = currentTime();
            if (poolEntry.isMarkedEvicted() || (elapsedMillis(poolEntry.lastAccessed, now) > aliveBypassWindowMs && !isConnectionAlive(poolEntry.connection))) {
               closeConnection(poolEntry, poolEntry.isMarkedEvicted() ? EVICTED_CONNECTION_MESSAGE : DEAD_CONNECTION_MESSAGE);
               timeout = hardTimeout - elapsedMillis(startTime);
            }
            else {
               metricsTracker.recordBorrowStats(poolEntry, startTime);
               return poolEntry.createProxyConnection(leakTaskFactory.schedule(poolEntry), now);
            }
         } while (timeout > 0L);

         metricsTracker.recordBorrowTimeoutStats(startTime);
         throw createTimeoutException(startTime);
      }
      catch (InterruptedException e) {
         Thread.currentThread().interrupt();
         throw new SQLException(poolName + " - Interrupted during connection acquisition", e);
      }
      finally {
         suspendResumeLock.release();
      }
   }

   
Shutdown the pool, closing all idle connections and aborting or closing
active connections.

Throws:
  • InterruptedException – thrown if the thread is interrupted during shutdown
/**
    * Shutdown the pool, closing all idle connections and aborting or closing
    * active connections.
    *
    * @throws InterruptedException thrown if the thread is interrupted during shutdown
    */
   public synchronized void shutdown() throws InterruptedException
   {
      try {
         poolState = POOL_SHUTDOWN;

         if (addConnectionExecutor == null) { // pool never started
            return;
         }

         logPoolState("Before shutdown ");

         if (houseKeeperTask != null) {
            houseKeeperTask.cancel(false);
            houseKeeperTask = null;
         }

         softEvictConnections();

         addConnectionExecutor.shutdown();
         addConnectionExecutor.awaitTermination(getLoginTimeout(), SECONDS);

         destroyHouseKeepingExecutorService();

         connectionBag.close();

         final ExecutorService assassinExecutor = createThreadPoolExecutor(config.getMaximumPoolSize(), poolName + " connection assassinator",
                                                                           config.getThreadFactory(), new ThreadPoolExecutor.CallerRunsPolicy());
         try {
            final long start = currentTime();
            do {
               abortActiveConnections(assassinExecutor);
               softEvictConnections();
            } while (getTotalConnections() > 0 && elapsedMillis(start) < SECONDS.toMillis(10));
         }
         finally {
            assassinExecutor.shutdown();
            assassinExecutor.awaitTermination(10L, SECONDS);
         }

         shutdownNetworkTimeoutExecutor();
         closeConnectionExecutor.shutdown();
         closeConnectionExecutor.awaitTermination(10L, SECONDS);
      }
      finally {
         logPoolState("After shutdown ");
         handleMBeans(this, false);
         metricsTracker.close();
      }
   }

   
Evict a Connection from the pool.

Params:
/**
    * Evict a Connection from the pool.
    *
    * @param connection the Connection to evict (actually a {@link ProxyConnection})
    */
   public void evictConnection(Connection connection)
   {
      ProxyConnection proxyConnection = (ProxyConnection) connection;
      proxyConnection.cancelLeakTask();

      try {
         softEvictConnection(proxyConnection.getPoolEntry(), "(connection evicted by user)", !connection.isClosed() /* owner */);
      }
      catch (SQLException e) {
         // unreachable in HikariCP, but we're still forced to catch it
      }
   }

   
Set a metrics registry to be used when registering metrics collectors.  The HikariDataSource prevents this
method from being called more than once.

Params:
  • metricRegistry – the metrics registry instance to use
/**
    * Set a metrics registry to be used when registering metrics collectors.  The HikariDataSource prevents this
    * method from being called more than once.
    *
    * @param metricRegistry the metrics registry instance to use
    */
   public void setMetricRegistry(Object metricRegistry)
   {
      if (metricRegistry != null && safeIsAssignableFrom(metricRegistry, "com.codahale.metrics.MetricRegistry")) {
         setMetricsTrackerFactory(new CodahaleMetricsTrackerFactory((MetricRegistry) metricRegistry));
      }
      else if (metricRegistry != null && safeIsAssignableFrom(metricRegistry, "io.micrometer.core.instrument.MeterRegistry")) {
         setMetricsTrackerFactory(new MicrometerMetricsTrackerFactory((MeterRegistry) metricRegistry));
      }
      else {
         setMetricsTrackerFactory(null);
      }
   }

   
Set the MetricsTrackerFactory to be used to create the IMetricsTracker instance used by the pool.

Params:
  • metricsTrackerFactory – an instance of a class that subclasses MetricsTrackerFactory
/**
    * Set the MetricsTrackerFactory to be used to create the IMetricsTracker instance used by the pool.
    *
    * @param metricsTrackerFactory an instance of a class that subclasses MetricsTrackerFactory
    */
   public void setMetricsTrackerFactory(MetricsTrackerFactory metricsTrackerFactory)
   {
      if (metricsTrackerFactory != null) {
         this.metricsTracker = new MetricsTrackerDelegate(metricsTrackerFactory.create(config.getPoolName(), getPoolStats()));
      }
      else {
         this.metricsTracker = new NopMetricsTrackerDelegate();
      }
   }

   
Set the health check registry to be used when registering health checks.  Currently only Codahale health
checks are supported.

Params:
  • healthCheckRegistry – the health check registry instance to use
/**
    * Set the health check registry to be used when registering health checks.  Currently only Codahale health
    * checks are supported.
    *
    * @param healthCheckRegistry the health check registry instance to use
    */
   public void setHealthCheckRegistry(Object healthCheckRegistry)
   {
      if (healthCheckRegistry != null) {
         CodahaleHealthChecker.registerHealthChecks(this, config, (HealthCheckRegistry) healthCheckRegistry);
      }
   }

   // ***********************************************************************
   //                        IBagStateListener callback
   // ***********************************************************************

   
{@inheritDoc} 
/** {@inheritDoc} */
   @Override
   public void addBagItem(final int waiting)
   {
      final boolean shouldAdd = waiting - addConnectionQueue.size() >= 0; // Yes, >= is intentional.
      if (shouldAdd) {
         addConnectionExecutor.submit(poolEntryCreator);
      }
   }

   // ***********************************************************************
   //                        HikariPoolMBean methods
   // ***********************************************************************

   
{@inheritDoc} 
/** {@inheritDoc} */
   @Override
   public int getActiveConnections()
   {
      return connectionBag.getCount(STATE_IN_USE);
   }

   
{@inheritDoc} 
/** {@inheritDoc} */
   @Override
   public int getIdleConnections()
   {
      return connectionBag.getCount(STATE_NOT_IN_USE);
   }

   
{@inheritDoc} 
/** {@inheritDoc} */
   @Override
   public int getTotalConnections()
   {
      return connectionBag.size();
   }

   
{@inheritDoc} 
/** {@inheritDoc} */
   @Override
   public int getThreadsAwaitingConnection()
   {
      return connectionBag.getWaitingThreadCount();
   }

   
{@inheritDoc} 
/** {@inheritDoc} */
   @Override
   public void softEvictConnections()
   {
      connectionBag.values().forEach(poolEntry -> softEvictConnection(poolEntry, "(connection evicted)", false /* not owner */));
   }

   
{@inheritDoc} 
/** {@inheritDoc} */
   @Override
   public synchronized void suspendPool()
   {
      if (suspendResumeLock == SuspendResumeLock.FAUX_LOCK) {
         throw new IllegalStateException(poolName + " - is not suspendable");
      }
      else if (poolState != POOL_SUSPENDED) {
         suspendResumeLock.suspend();
         poolState = POOL_SUSPENDED;
      }
   }

   
{@inheritDoc} 
/** {@inheritDoc} */
   @Override
   public synchronized void resumePool()
   {
      if (poolState == POOL_SUSPENDED) {
         poolState = POOL_NORMAL;
         fillPool();
         suspendResumeLock.resume();
      }
   }

   // ***********************************************************************
   //                           Package methods
   // ***********************************************************************

   
Log the current pool state at debug level.

Params:
  • prefix – an optional prefix to prepend the log message
/**
    * Log the current pool state at debug level.
    *
    * @param prefix an optional prefix to prepend the log message
    */
   void logPoolState(String... prefix)
   {
      if (logger.isDebugEnabled()) {
         logger.debug("{} - {}stats (total={}, active={}, idle={}, waiting={})",
                      poolName, (prefix.length > 0 ? prefix[0] : ""),
                      getTotalConnections(), getActiveConnections(), getIdleConnections(), getThreadsAwaitingConnection());
      }
   }

   
Recycle PoolEntry (add back to the pool)

Params:
  • poolEntry – the PoolEntry to recycle
/**
    * Recycle PoolEntry (add back to the pool)
    *
    * @param poolEntry the PoolEntry to recycle
    */
   @Override
   void recycle(final PoolEntry poolEntry)
   {
      metricsTracker.recordConnectionUsage(poolEntry);

      connectionBag.requite(poolEntry);
   }

   
Permanently close the real (underlying) connection (eat any exception).

Params:
  • poolEntry – poolEntry having the connection to close
  • closureReason – reason to close
/**
    * Permanently close the real (underlying) connection (eat any exception).
    *
    * @param poolEntry poolEntry having the connection to close
    * @param closureReason reason to close
    */
   void closeConnection(final PoolEntry poolEntry, final String closureReason)
   {
      if (connectionBag.remove(poolEntry)) {
         final Connection connection = poolEntry.close();
         closeConnectionExecutor.execute(() -> {
            quietlyCloseConnection(connection, closureReason);
            if (poolState == POOL_NORMAL) {
               fillPool();
            }
         });
      }
   }

   @SuppressWarnings("unused")
   int[] getPoolStateCounts()
   {
      return connectionBag.getStateCounts();
   }


   // ***********************************************************************
   //                           Private methods
   // ***********************************************************************

   
Creating new poolEntry.  If maxLifetime is configured, create a future End-of-life task with 2.5% variance from
the maxLifetime time to ensure there is no massive die-off of Connections in the pool.

/**
    * Creating new poolEntry.  If maxLifetime is configured, create a future End-of-life task with 2.5% variance from
    * the maxLifetime time to ensure there is no massive die-off of Connections in the pool.
    */
   private PoolEntry createPoolEntry()
   {
      try {
         final PoolEntry poolEntry = newPoolEntry();

         final long maxLifetime = config.getMaxLifetime();
         if (maxLifetime > 0) {
            // variance up to 2.5% of the maxlifetime
            final long variance = maxLifetime > 10_000 ? ThreadLocalRandom.current().nextLong( maxLifetime / 40 ) : 0;
            final long lifetime = maxLifetime - variance;
            poolEntry.setFutureEol(houseKeepingExecutorService.schedule(
               () -> {
                  if (softEvictConnection(poolEntry, "(connection has passed maxLifetime)", false /* not owner */)) {
                     addBagItem(connectionBag.getWaitingThreadCount());
                  }
               },
               lifetime, MILLISECONDS));
         }

         return poolEntry;
      }
      catch (ConnectionSetupException e) {
         if (poolState == POOL_NORMAL) { // we check POOL_NORMAL to avoid a flood of messages if shutdown() is running concurrently
            logger.error("{} - Error thrown while acquiring connection from data source", poolName, e.getCause());
            lastConnectionFailure.set(e);
         }
         return null;
      }
      catch (SQLException e) {
         if (poolState == POOL_NORMAL) { // we check POOL_NORMAL to avoid a flood of messages if shutdown() is running concurrently
            logger.debug("{} - Cannot acquire connection from data source", poolName, e);
            lastConnectionFailure.set(new ConnectionSetupException(e));
         }
         return null;
      }
      catch (Exception e) {
         if (poolState == POOL_NORMAL) { // we check POOL_NORMAL to avoid a flood of messages if shutdown() is running concurrently
            logger.error("{} - Error thrown while acquiring connection from data source", poolName, e);
            lastConnectionFailure.set(new ConnectionSetupException(e));
         }
         return null;
      }
   }

   
Fill pool up from current idle connections (as they are perceived at the point of execution) to minimumIdle connections.

/**
    * Fill pool up from current idle connections (as they are perceived at the point of execution) to minimumIdle connections.
    */
   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);
      }
   }

   
Attempt to abort or close active connections.

Params:
  • assassinExecutor – the ExecutorService to pass to Connection.abort()
/**
    * Attempt to abort or close active connections.
    *
    * @param assassinExecutor the ExecutorService to pass to Connection.abort()
    */
   private void abortActiveConnections(final ExecutorService assassinExecutor)
   {
      for (PoolEntry poolEntry : connectionBag.values(STATE_IN_USE)) {
         Connection connection = poolEntry.close();
         try {
            connection.abort(assassinExecutor);
         }
         catch (Throwable e) {
            quietlyCloseConnection(connection, "(connection aborted during shutdown)");
         }
         finally {
            connectionBag.remove(poolEntry);
         }
      }
   }

   
If initializationFailFast is configured, check that we have DB connectivity.

Throws:
  • PoolInitializationException – if fails to create or validate connection
See Also:
/**
    * If initializationFailFast is configured, check that we have DB connectivity.
    *
    * @throws PoolInitializationException if fails to create or validate connection
    * @see HikariConfig#setInitializationFailTimeout(long)
    */
   private void checkFailFast()
   {
      final long initializationTimeout = config.getInitializationFailTimeout();
      if (initializationTimeout < 0) {
         return;
      }

      final long startTime = currentTime();
      do {
         final PoolEntry poolEntry = createPoolEntry();
         if (poolEntry != null) {
            if (config.getMinimumIdle() > 0) {
               connectionBag.add(poolEntry);
               logger.debug("{} - Added connection {}", poolName, poolEntry.connection);
            }
            else {
               quietlyCloseConnection(poolEntry.close(), "(initialization check complete and minimumIdle is zero)");
            }

            return;
         }

         if (getLastConnectionFailure() instanceof ConnectionSetupException) {
            throwPoolInitializationException(getLastConnectionFailure().getCause());
         }

         quietlySleep(SECONDS.toMillis(1));
      } while (elapsedMillis(startTime) < initializationTimeout);

      if (initializationTimeout > 0) {
         throwPoolInitializationException(getLastConnectionFailure());
      }
   }

   
Log the Throwable that caused pool initialization to fail, and then throw a PoolInitializationException with
that cause attached.

Params:
  • t – the Throwable that caused the pool to fail to initialize (possibly null)
/**
    * Log the Throwable that caused pool initialization to fail, and then throw a PoolInitializationException with
    * that cause attached.
    *
    * @param t the Throwable that caused the pool to fail to initialize (possibly null)
    */
   private void throwPoolInitializationException(Throwable t)
   {
      logger.error("{} - Exception during pool initialization.", poolName, t);
      destroyHouseKeepingExecutorService();
      throw new PoolInitializationException(t);
   }

   
"Soft" evict a Connection (/PoolEntry) from the pool. If this method is being called by the user directly through HikariDataSource.evictConnection(Connection) then owner is true. If the caller is the owner, or if the Connection is idle (i.e. can be "reserved" in the ConcurrentBag), then we can close the connection immediately. Otherwise, we leave it "marked" for eviction so that it is evicted the next time someone tries to acquire it from the pool. 
Params:
  • poolEntry – the PoolEntry (/Connection) to "soft" evict from the pool
  • reason – the reason that the connection is being evicted
  • owner – true if the caller is the owner of the connection, false otherwise
Returns:true if the connection was evicted (closed), false if it was merely marked for eviction
/**
    * "Soft" evict a Connection (/PoolEntry) from the pool.  If this method is being called by the user directly
    * through {@link com.zaxxer.hikari.HikariDataSource#evictConnection(Connection)} then {@code owner} is {@code true}.
    *
    * If the caller is the owner, or if the Connection is idle (i.e. can be "reserved" in the {@link ConcurrentBag}),
    * then we can close the connection immediately.  Otherwise, we leave it "marked" for eviction so that it is evicted
    * the next time someone tries to acquire it from the pool.
    *
    * @param poolEntry the PoolEntry (/Connection) to "soft" evict from the pool
    * @param reason the reason that the connection is being evicted
    * @param owner true if the caller is the owner of the connection, false otherwise
    * @return true if the connection was evicted (closed), false if it was merely marked for eviction
    */
   private boolean softEvictConnection(final PoolEntry poolEntry, final String reason, final boolean owner)
   {
      poolEntry.markEvicted();
      if (owner || connectionBag.reserve(poolEntry)) {
         closeConnection(poolEntry, reason);
         return true;
      }

      return false;
   }

   
Create/initialize the Housekeeping service ScheduledExecutorService. If the user specified an Executor to be used in the HikariConfig, then we use that. If no Executor was specified (typical), then create an Executor and configure it. 
Returns:either the user specified ScheduledExecutorService, or the one we created
/**
    * Create/initialize the Housekeeping service {@link ScheduledExecutorService}.  If the user specified an Executor
    * to be used in the {@link HikariConfig}, then we use that.  If no Executor was specified (typical), then create
    * an Executor and configure it.
    *
    * @return either the user specified {@link ScheduledExecutorService}, or the one we created
    */
   private ScheduledExecutorService initializeHouseKeepingExecutorService()
   {
      if (config.getScheduledExecutor() == null) {
         final ThreadFactory threadFactory = Optional.ofNullable(config.getThreadFactory()).orElseGet(() -> new DefaultThreadFactory(poolName + " housekeeper", true));
         final ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(1, threadFactory, new ThreadPoolExecutor.DiscardPolicy());
         executor.setExecuteExistingDelayedTasksAfterShutdownPolicy(false);
         executor.setRemoveOnCancelPolicy(true);
         return executor;
      }
      else {
         return config.getScheduledExecutor();
      }
   }

   
Destroy (/shutdown) the Housekeeping service Executor, if it was the one that we created.

/**
    * Destroy (/shutdown) the Housekeeping service Executor, if it was the one that we created.
    */
   private void destroyHouseKeepingExecutorService()
   {
      if (config.getScheduledExecutor() == null) {
         houseKeepingExecutorService.shutdownNow();
      }
   }

   
Create a PoolStats instance that will be used by metrics tracking, with a pollable resolution of 1 second.

Returns:a PoolStats instance
/**
    * Create a PoolStats instance that will be used by metrics tracking, with a pollable resolution of 1 second.
    *
    * @return a PoolStats instance
    */
   private PoolStats getPoolStats()
   {
      return new PoolStats(SECONDS.toMillis(1)) {
         @Override
         protected void update() {
            this.pendingThreads = HikariPool.this.getThreadsAwaitingConnection();
            this.idleConnections = HikariPool.this.getIdleConnections();
            this.totalConnections = HikariPool.this.getTotalConnections();
            this.activeConnections = HikariPool.this.getActiveConnections();
            this.maxConnections = config.getMaximumPoolSize();
            this.minConnections = config.getMinimumIdle();
         }
      };
   }

   
Create a timeout exception (specifically, SQLTransientConnectionException) to be thrown, because a timeout occurred when trying to acquire a Connection from the pool. If there was an underlying cause for the timeout, e.g. a SQLException thrown by the driver while trying to create a new Connection, then use the SQL State from that exception as our own and additionally set that exception as the "next" SQLException inside of our exception. As a side-effect, log the timeout failure at DEBUG, and record the timeout failure in the metrics tracker. 
Params:
  • startTime – the start time (timestamp) of the acquisition attempt
Returns:a SQLException to be thrown from getConnection()
/**
    * Create a timeout exception (specifically, {@link SQLTransientConnectionException}) to be thrown, because a
    * timeout occurred when trying to acquire a Connection from the pool.  If there was an underlying cause for the
    * timeout, e.g. a SQLException thrown by the driver while trying to create a new Connection, then use the
    * SQL State from that exception as our own and additionally set that exception as the "next" SQLException inside
    * of our exception.
    *
    * As a side-effect, log the timeout failure at DEBUG, and record the timeout failure in the metrics tracker.
    *
    * @param startTime the start time (timestamp) of the acquisition attempt
    * @return a SQLException to be thrown from {@link #getConnection()}
    */
   private SQLException createTimeoutException(long startTime)
   {
      logPoolState("Timeout failure ");
      metricsTracker.recordConnectionTimeout();

      String sqlState = null;
      final Throwable originalException = getLastConnectionFailure();
      if (originalException instanceof SQLException) {
         sqlState = ((SQLException) originalException).getSQLState();
      }
      final SQLException connectionException = new SQLTransientConnectionException(poolName + " - Connection is not available, request timed out after " + elapsedMillis(startTime) + "ms.", sqlState, originalException);
      if (originalException instanceof SQLException) {
         connectionException.setNextException((SQLException) originalException);
      }

      return connectionException;
   }


   // ***********************************************************************
   //                      Non-anonymous Inner-classes
   // ***********************************************************************

   
Creating and adding poolEntries (connections) to the pool.

/**
    * Creating and adding poolEntries (connections) to the pool.
    */
   private final class PoolEntryCreator implements Callable<Boolean>
   {
      private final String loggingPrefix;

      PoolEntryCreator(String loggingPrefix)
      {
         this.loggingPrefix = loggingPrefix;
      }

      @Override
      public Boolean call()
      {
         long sleepBackoff = 250L;
         while (poolState == POOL_NORMAL && shouldCreateAnotherConnection()) {
            final PoolEntry poolEntry = createPoolEntry();
            if (poolEntry != null) {
               connectionBag.add(poolEntry);
               logger.debug("{} - Added connection {}", poolName, poolEntry.connection);
               if (loggingPrefix != null) {
                  logPoolState(loggingPrefix);
               }
               return Boolean.TRUE;
            }

            // failed to get connection from db, sleep and retry
            quietlySleep(sleepBackoff);
            sleepBackoff = Math.min(SECONDS.toMillis(10), Math.min(connectionTimeout, (long) (sleepBackoff * 1.5)));
         }
         // Pool is suspended or shutdown or at max size
         return Boolean.FALSE;
      }

      
We only create connections if we need another idle connection or have threads still waiting
for a new connection.  Otherwise we bail out of the request to create.

Returns:true if we should create a connection, false if the need has disappeared
/**
       * We only create connections if we need another idle connection or have threads still waiting
       * for a new connection.  Otherwise we bail out of the request to create.
       *
       * @return true if we should create a connection, false if the need has disappeared
       */
      private synchronized boolean shouldCreateAnotherConnection() {
         return getTotalConnections() < config.getMaximumPoolSize() &&
            (connectionBag.getWaitingThreadCount() > 0 || getIdleConnections() < config.getMinimumIdle());
      }
   }

   
The house keeping task to retire and maintain minimum idle connections.

/**
    * The house keeping task to retire and maintain minimum idle connections.
    */
   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  ";

               final List<PoolEntry> notInUse = connectionBag.values(STATE_NOT_IN_USE);
               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);

            fillPool(); // Try to maintain minimum connections
         }
         catch (Exception e) {
            logger.error("Unexpected exception in housekeeping task", e);
         }
      }
   }

   public static class PoolInitializationException extends RuntimeException
   {
      private static final long serialVersionUID = 929872118275916520L;

      
Construct an exception, possibly wrapping the provided Throwable as the cause.

Params:
  • t – the Throwable to wrap
/**
       * Construct an exception, possibly wrapping the provided Throwable as the cause.
       * @param t the Throwable to wrap
       */
      public PoolInitializationException(Throwable t)
      {
         super("Failed to initialize pool: " + t.getMessage(), t);
      }
   }
}