聊聊hikari连接池的isAllowPoolSuspension

序

本文主要研究一下hikari连接池的isAllowPoolSuspension属性

实例代码

    @Test
    public void testPoolSuspend() throws SQLException {
        Connection conn = dataSource.getConnection();
        System.out.println("begin to suspend pool");
        ((HikariDataSource)dataSource).suspendPool();
        Connection conn2 = dataSource.getConnection();
        System.out.println("finish");
    }

suspend

begin to suspend pool

java.lang.IllegalStateException: HikariPool-1 - is not suspendable

    at com.zaxxer.hikari.pool.HikariPool.suspendPool(HikariPool.java:372)
    at com.zaxxer.hikari.HikariDataSource.suspendPool(HikariDataSource.java:326)
    at com.example.demo.HikariDemoApplicationTests.testPoolSuspend(HikariDemoApplicationTests.java:37)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:73)
    at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:83)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:234)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:74)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

当没有设置的allow-pool-suspension=true时候，抛出java.lang.IllegalStateException: HikariPool-1 - is not suspendable

allow-pool-suspension=true

HikariCP-2.7.6-sources.jar!/com/zaxxer/hikari/pool/HikariPool.java

   /**
    * 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());

      registerMBeans(this);

      ThreadFactory threadFactory = config.getThreadFactory();

      LinkedBlockingQueue<Runnable> addConnectionQueue = new LinkedBlockingQueue<>(config.getMaximumPoolSize());
      this.addConnectionQueue = unmodifiableCollection(addConnectionQueue);
      this.addConnectionExecutor = createThreadPoolExecutor(addConnectionQueue, 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, HOUSEKEEPING_PERIOD_MS, MILLISECONDS);
   }

如果isAllowPoolSuspension为ture，则suspendResumeLock是一个真实的SuspendResumeLock，否则是SuspendResumeLock.FAUX_LOCK

SuspendResumeLock

/**
 * This class implements a lock that can be used to suspend and resume the pool.  It
 * also provides a faux implementation that is used when the feature is disabled that
 * hopefully gets fully "optimized away" by the JIT.
 *
 * @author Brett Wooldridge
 */
public class SuspendResumeLock
{
   public static final SuspendResumeLock FAUX_LOCK = new SuspendResumeLock(false) {
      @Override
      public void acquire() {}

      @Override
      public void release() {}
      
      @Override
      public void suspend() {}

      @Override
      public void resume() {}
   };

   private static final int MAX_PERMITS = 10000;
   private final Semaphore acquisitionSemaphore;

   /**
    * Default constructor
    */
   public SuspendResumeLock()
   {
      this(true);
   }

   private SuspendResumeLock(final boolean createSemaphore)
   {
      acquisitionSemaphore = (createSemaphore ? new Semaphore(MAX_PERMITS, true) : null);
   }

   public void acquire()
   {
      acquisitionSemaphore.acquireUninterruptibly();
   }

   public void release()
   {
      acquisitionSemaphore.release();
   }

   public void suspend()
   {
      acquisitionSemaphore.acquireUninterruptibly(MAX_PERMITS);
   }

   public void resume()
   {
      acquisitionSemaphore.release(MAX_PERMITS);
   }
}

FAUX_LOCK是一个空方法，false表示不创建信号量

suspend方法一次性消耗了MAX_PERMITS信号量，这个方法被调用之后，之后getConnection方法都获取不到连接，永远阻塞在suspendResumeLock.acquire();

resume方法一次性释放MAX_PERMITS信号量

HikariPool.getConnection

HikariCP-2.7.6-sources.jar!/com/zaxxer/hikari/pool/HikariPool.java

   /**
    * 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.
    *
    * @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) > ALIVE_BYPASS_WINDOW_MS && !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();
      }
   }

可以看到getConnection是先获取信号量，最后不管获取成功还是超时，finally里头去释放这个信号量
这里的hardTimeout就是从连接池借用connection的超时时间

小结

isAllowPoolSuspension用来标记释放允许暂停连接池，一旦被暂停，所有的getConnection方法都会被阻塞。可能的用处就是用来实现chaosmonkey，模拟数据库连接故障。作者在github上的解释是可以用来做些配置修改：暂停连接池，修改连接池配置或dns配置，soft-evit既有连接，然后恢复连接池。

doc

• configuration-knobs-baby
• Can HikariCP offer new "suspend" function that can immediately throw "suspend“ exception