// 连接池中保存 连接 的集合
private final CopyOnWriteArrayList<T> sharedList;

 
public T borrow(long timeout, final TimeUnit timeUnit) throws InterruptedException
   {
      // Try the thread-local list first
      final var list = threadList.get();
      for (int i = list.size() - 1; i >= 0; i--) {
         final var entry = list.remove(i);
         @SuppressWarnings("unchecked")
         final T bagEntry = weakThreadLocals ? ((WeakReference<T>) entry).get() : (T) entry;
         if (bagEntry != null && bagEntry.compareAndSet(STATE_NOT_IN_USE, STATE_IN_USE)) {
            return bagEntry;
         }
      }
 
      // Otherwise, scan the shared list ... then poll the handoff queue
      final int waiting = waiters.incrementAndGet();
      try {
         for (T bagEntry : sharedList) {
            if (bagEntry.compareAndSet(STATE_NOT_IN_USE, STATE_IN_USE)) {
               // If we may have stolen another waiter's connection, request another bag add.
               if (waiting > 1) {
                  listener.addBagItem(waiting - 1);
               }
               return bagEntry;
            }
         }
 
         listener.addBagItem(waiting);
 
         timeout = timeUnit.toNanos(timeout);
         do {
            final var start = currentTime();
            final T bagEntry = handoffQueue.poll(timeout, NANOSECONDS);
            if (bagEntry == null || bagEntry.compareAndSet(STATE_NOT_IN_USE, STATE_IN_USE)) {
               return bagEntry;
            }
 
            timeout -= elapsedNanos(start);
         } while (timeout > 10_000);
 
         return null;
      }
      finally {
         waiters.decrementAndGet();
      }
   }
 
 

 public void requite(final T bagEntry)
   {
      bagEntry.setState(STATE_NOT_IN_USE);
 
      for (var i = 0; waiters.get() > 0; i++) {
         if (bagEntry.getState() != STATE_NOT_IN_USE || handoffQueue.offer(bagEntry)) {
            return;
         }
         else if ((i & 0xff) == 0xff) {
            parkNanos(MICROSECONDS.toNanos(10));
         }
         else {
            Thread.yield();
         }
      }
 
      final var threadLocalList = threadList.get();
      if (threadLocalList.size() < 50) {
         threadLocalList.add(weakThreadLocals ? new WeakReference<>(bagEntry) : bagEntry);
      }
   }
 

   public void add(final T bagEntry)
   {
      if (closed) {
         LOGGER.info("ConcurrentBag has been closed, ignoring add()");
         throw new IllegalStateException("ConcurrentBag has been closed, ignoring add()");
      }
 
      sharedList.add(bagEntry);
 
      // spin until a thread takes it or none are waiting
      while (waiters.get() > 0 && bagEntry.getState() == STATE_NOT_IN_USE && !handoffQueue.offer(bagEntry)) {
         Thread.yield();
      }
   }

   public boolean remove(final T bagEntry)
   {
      if (!bagEntry.compareAndSet(STATE_IN_USE, STATE_REMOVED) && !bagEntry.compareAndSet(STATE_RESERVED, STATE_REMOVED) && !closed) {
         LOGGER.warn("Attempt to remove an object from the bag that was not borrowed or reserved: {}", bagEntry);
         return false;
      }
 
      final boolean removed = sharedList.remove(bagEntry);
      if (!removed && !closed) {
         LOGGER.warn("Attempt to remove an object from the bag that does not exist: {}", bagEntry);
      }
 
      threadList.get().remove(bagEntry);
 
      return removed;
   }

   private final HikariPool fastPathPool;
   private volatile HikariPool pool;

 public Connection getConnection() throws SQLException
   {
      if (fastPathPool != null) {
         return fastPathPool.getConnection();
      }
 
      // 双重检查 pool 的初始化
      HikariPool result = pool;
      if (result == null) {
         synchronized (this) {
            result = pool;
            if (result == null) {
               validate();
               LOGGER.info("{} - Starting...", getPoolName());
               try {
                  pool = result = new HikariPool(this);
                  this.seal();
               }
               catch (PoolInitializationException pie) {
                  if (pie.getCause() instanceof SQLException) {
                     throw (SQLException) pie.getCause();
                  }
                  else {
                     throw pie;
                  }
               }
               LOGGER.info("{} - Start completed.", getPoolName());
            }
         }
      }
 
      return result.getConnection();
   }

<plugin>
    <!-- Generate proxies -->
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>exec-maven-plugin</artifactId>
    <version>1.6.0</version>
    <extensions>true</extensions>
    <executions>
       <execution>
          <phase>compile</phase>
          <!-- phase>generate-test-sources</phase -->
          <goals>
             <goal>exec</goal>
          </goals>
       </execution>
    </executions>
    <configuration>
       <executable>java</executable>
       <arguments>
          <argument>-cp</argument>
          <argument>${project.build.outputDirectory}${path.separator}${maven.compile.classpath}</argument>
          <!-- 会执行 JavassistProxyFactory 类的 main 方法 -->
          <argument>com.zaxxer.hikari.util.JavassistProxyFactory</argument>
          <argument>${project.basedir}${file.separator}</argument>
       </arguments>
    </configuration>
 </plugin>