Simplify ActiveChannelTracker to not store channels

It previously needed to store channels for purging of network
connections on error. Now this functionality is not needed because
driver never performs an active purge.

This commit makes `ActiveChannelTracker` only store number of active
connections per host, not the actual connections.

Author: lutovich

driver/src/main/java/org/neo4j/driver/internal/async/pool/ActiveChannelTracker.java

@@ -20,10 +20,10 @@
 
 import io.netty.channel.Channel;
 import io.netty.channel.pool.ChannelPoolHandler;
-import io.netty.util.internal.ConcurrentSet;
 
+import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import org.neo4j.driver.internal.BoltServerAddress;
 import org.neo4j.driver.v1.Logger;
@@ -33,12 +33,11 @@
 
 public class ActiveChannelTracker implements ChannelPoolHandler
 {
-    private final ConcurrentMap<BoltServerAddress,ConcurrentSet<Channel>> addressToActiveChannelCount;
+    private final Map<BoltServerAddress,AtomicInteger> addressToActiveChannelCount = new ConcurrentHashMap<>();
     private final Logger log;
 
     public ActiveChannelTracker( Logging logging )
     {
-        this.addressToActiveChannelCount = new ConcurrentHashMap<>();
         this.log = logging.getLog( getClass().getSimpleName() );
     }
 
@@ -65,52 +64,25 @@ public void channelCreated( Channel channel )
 
     public int activeChannelCount( BoltServerAddress address )
     {
-        ConcurrentSet<Channel> activeChannels = addressToActiveChannelCount.get( address );
-        return activeChannels == null ? 0 : activeChannels.size();
-    }
-
-    public void purge( BoltServerAddress address )
-    {
-        ConcurrentSet<Channel> activeChannels = addressToActiveChannelCount.remove( address );
-        if ( activeChannels != null )
-        {
-            for ( Channel channel : activeChannels )
-            {
-                channel.close();
-            }
-        }
+        AtomicInteger count = addressToActiveChannelCount.get( address );
+        return count == null ? 0 : count.get();
     }
 
     private void channelActive( Channel channel )
     {
         BoltServerAddress address = serverAddress( channel );
-        ConcurrentSet<Channel> activeChannels = addressToActiveChannelCount.get( address );
-        if ( activeChannels == null )
-        {
-            ConcurrentSet<Channel> newActiveChannels = new ConcurrentSet<>();
-            ConcurrentSet<Channel> existingActiveChannels = addressToActiveChannelCount.putIfAbsent( address,
-                    newActiveChannels );
-            if ( existingActiveChannels == null )
-            {
-                activeChannels = newActiveChannels;
-            }
-            else
-            {
-                activeChannels = existingActiveChannels;
-            }
-        }
-
-        activeChannels.add( channel );
+        AtomicInteger count = addressToActiveChannelCount.computeIfAbsent( address, k -> new AtomicInteger() );
+        count.incrementAndGet();
     }
 
     private void channelInactive( Channel channel )
     {
         BoltServerAddress address = serverAddress( channel );
-        ConcurrentSet<Channel> activeChannels = addressToActiveChannelCount.get( address );
-        if ( activeChannels == null )
+        AtomicInteger count = addressToActiveChannelCount.get( address );
+        if ( count == null )
         {
-            throw new IllegalStateException( "No channels exist for address '" + address + "'" );
+            throw new IllegalStateException( "No count exist for address '" + address + "'" );
         }
-        activeChannels.remove( channel );
+        count.decrementAndGet();
     }
 }

driver/src/test/java/org/neo4j/driver/internal/async/pool/ActiveChannelTrackerTest.java

@@ -26,12 +26,10 @@
 
 import static org.hamcrest.Matchers.instanceOf;
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import static org.neo4j.driver.internal.async.ChannelAttributes.setServerAddress;
 import static org.neo4j.driver.internal.logging.DevNullLogging.DEV_NULL_LOGGING;
-import static org.neo4j.driver.v1.util.TestUtil.await;
 
 public class ActiveChannelTrackerTest
 {
@@ -106,35 +104,6 @@ public void shouldReturnZeroActiveCountForUnknownAddress()
         assertEquals( 0, tracker.activeChannelCount( address ) );
     }
 
-    @Test
-    public void shouldPruneForMissingAddress()
-    {
-        assertEquals( 0, tracker.activeChannelCount( address ) );
-        tracker.purge( address );
-        assertEquals( 0, tracker.activeChannelCount( address ) );
-    }
-
-    @Test
-    public void shouldPruneForExistingAddress()
-    {
-        Channel channel1 = newChannel();
-        Channel channel2 = newChannel();
-        Channel channel3 = newChannel();
-
-        tracker.channelAcquired( channel1 );
-        tracker.channelAcquired( channel2 );
-        tracker.channelAcquired( channel3 );
-
-        assertEquals( 3, tracker.activeChannelCount( address ) );
-
-        tracker.purge( address );
-
-        assertEquals( 0, tracker.activeChannelCount( address ) );
-        assertNull( await( channel1.closeFuture() ) );
-        assertNull( await( channel2.closeFuture() ) );
-        assertNull( await( channel3.closeFuture() ) );
-    }
-
     private Channel newChannel()
     {
         EmbeddedChannel channel = new EmbeddedChannel();