Don't add the same connection multiple times

The same connections was being added to the queue if close was called more
than once. Eventually the queue will be full and we close the connection, but
since the queue now contains multiple identical copies we will also close these.

driver/src/main/java/org/neo4j/driver/internal/net/pooling/PooledConnection.java

@@ -19,6 +19,7 @@
 package org.neo4j.driver.internal.net.pooling;
 
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.neo4j.driver.internal.net.BoltServerAddress;
 import org.neo4j.driver.internal.spi.Collector;
@@ -58,6 +59,7 @@ public class PooledConnection implements Connection
     private Runnable onError = null;
     private final Clock clock;
     private long lastUsed;
+    private final AtomicBoolean released = new AtomicBoolean( false );
 
     public PooledConnection( Connection delegate, Consumer<PooledConnection> release, Clock clock )
     {
@@ -67,8 +69,9 @@ public PooledConnection( Connection delegate, Consumer<PooledConnection> release
         this.lastUsed = clock.millis();
     }
 
-    public void updateUsageTimestamp()
+    public void setInUse()
     {
+        released.set(false);
         lastUsed = clock.millis();
     }
 
@@ -197,7 +200,10 @@ public void receiveOne()
      */
     public void close()
     {
-        release.accept( this );
+        if ( released.compareAndSet( false, true ))
+        {
+            release.accept( this );
+        }
         // put the full logic of deciding whether to dispose the connection or to put it back to
         // the pool into the release object
     }

driver/src/main/java/org/neo4j/driver/internal/net/pooling/SocketConnectionPool.java

@@ -115,7 +115,7 @@ public Connection acquire( BoltServerAddress address )
             conn = new PooledConnection( connect( address ), new
                     PooledConnectionReleaseConsumer( connections, stopped, new PooledConnectionValidator( this, poolSettings ) ), clock );
         }
-        conn.updateUsageTimestamp();
+        conn.setInUse();
         return conn;
     }
 

driver/src/test/java/org/neo4j/driver/internal/net/pooling/PooledConnectionTest.java

@@ -120,6 +120,40 @@ public void dispose()
         assertThat( flags[0], equalTo( false ) );
     }
 
+    @Test
+    public void shouldOnlyReturnOnceEventhougCloseIsBeingCalledMultipleTimes() throws Throwable
+    {
+        // Given
+        final BlockingQueue<PooledConnection> pool = new LinkedBlockingQueue<>(2);
+
+        final boolean[] flags = {false};
+
+        Connection conn = mock( Connection.class );
+        PooledConnectionReleaseConsumer releaseConsumer = new PooledConnectionReleaseConsumer( pool,
+                new AtomicBoolean( false ), VALID_CONNECTION );
+
+        PooledConnection pooledConnection = new PooledConnection( conn, releaseConsumer, Clock.SYSTEM )
+        {
+            @Override
+            public void dispose()
+            {
+                flags[0] = true;
+            }
+        };
+
+        // When
+        pooledConnection.close();
+        pooledConnection.close();
+        pooledConnection.close();
+        pooledConnection.close();
+        pooledConnection.close();
+
+        // Then
+        assertThat( pool, hasItem(pooledConnection) );
+        assertThat( pool.size(), equalTo( 1 ) );
+        assertThat( flags[0], equalTo( false ) );
+    }
+
     @Test
     public void shouldDisposeConnectionIfValidConnectionAndIdlePoolIsFull() throws Throwable
     {