Merge branch 'experimental' into dev

* experimental:
  Experimental concurrentbag fairness changes.  Starvation was observed under high load.

src/main/java/com/zaxxer/hikari/pool/PoolBagEntry.java

@@ -17,6 +17,7 @@ package com.zaxxer.hikari.pool;
 
 import java.sql.Connection;
 import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
 
@@ -44,7 +45,8 @@ public final class PoolBagEntry implements IConcurrentBagEntry
       this.connection = connection;
       this.lastAccess = System.currentTimeMillis();
 
-      final long maxLifetime = pool.configuration.getMaxLifetime();
+      final long variance = pool.configuration.getMaxLifetime() > 300_000 ? ThreadLocalRandom.current().nextLong(100_000) : 0;
+      final long maxLifetime = pool.configuration.getMaxLifetime() - variance;
       if (maxLifetime > 0) {
          endOfLife = pool.houseKeepingExecutorService.schedule(new Runnable() {
             public void run()

src/main/java/com/zaxxer/hikari/util/ConcurrentBag.java

@@ -58,9 +58,9 @@ public class ConcurrentBag<T extends IConcurrentBagEntry>
 
    protected final AbstractQueuedLongSynchronizer synchronizer;
    protected final CopyOnWriteArrayList<T> sharedList;
-   protected final AtomicLong sequence;
 
    private final ThreadLocal<ArrayList<WeakReference<IConcurrentBagEntry>>> threadList;
+   private final AtomicLong sequence;
    private final IBagStateListener listener;
    private volatile boolean closed;
 
@@ -310,22 +310,21 @@ public class ConcurrentBag<T extends IConcurrentBagEntry>
    /**
     * Our private synchronizer that handles notify/wait type semantics.
     */
-   private static final class Synchronizer extends AbstractQueuedLongSynchronizer
+   private final class Synchronizer extends AbstractQueuedLongSynchronizer
    {
       private static final long serialVersionUID = 104753538004341218L;
 
       @Override
-      protected long tryAcquireShared(long seq)
+      protected long tryAcquireShared(final long seq)
       {
-         return getState() > seq && !hasQueuedPredecessors() ? 1L : -1L;
+         return hasQueuedPredecessors() ? -1L : getState() - (seq + 1);
       }
 
       /** {@inheritDoc} */
       @Override
-      protected boolean tryReleaseShared(long updateSeq)
+      protected boolean tryReleaseShared(final long unreliableSequence)
       {
-         setState(updateSeq);
-
+         setState(sequence.get());
          return true;
       }
    }