Released memory retained by ExchangeSource

core/trino-main/src/main/java/io/trino/operator/DeduplicatingDirectExchangeBuffer.java

@@ -760,7 +760,7 @@ private static class ExchangeOutputSource
     {
         private final Set<TaskId> selectedTasks;
         private final QueryId queryId;
-        private final ListenableFuture<ExchangeSource> exchangeSourceFuture;
+        private ListenableFuture<ExchangeSource> exchangeSourceFuture;
 
         private ExchangeSource exchangeSource;
         private boolean finished;
@@ -848,6 +848,7 @@ public void close()
                 return;
             }
             finished = true;
+            exchangeSource = null;
             addCallback(exchangeSourceFuture, new FutureCallback<>()
             {
                 @Override
@@ -868,6 +869,7 @@ public void onFailure(Throwable ignored)
                     // It a failure occurred it is expected to be propagated by the getNext method
                 }
             }, directExecutor());
+            exchangeSourceFuture = null;
         }
     }
 }

core/trino-main/src/main/java/io/trino/operator/ExchangeOperator.java

@@ -16,6 +16,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.util.concurrent.ListenableFuture;
 import com.google.common.util.concurrent.SettableFuture;
+import io.airlift.log.Logger;
 import io.airlift.slice.Slice;
 import io.trino.connector.CatalogName;
 import io.trino.exchange.ExchangeManagerRegistry;
@@ -54,6 +55,8 @@
 public class ExchangeOperator
         implements SourceOperator
 {
+    private static final Logger log = Logger.get(ExchangeOperator.class);
+
     public static final CatalogName REMOTE_CONNECTOR_ID = new CatalogName("$remote");
 
     public static class ExchangeOperatorFactory
@@ -459,15 +462,21 @@ public void close()
     private static class SpoolingExchangeDataSource
             implements ExchangeDataSource
     {
-        private final ExchangeSource exchangeSource;
+        // This field is not final to allow releasing the memory retained by the ExchangeSource instance.
+        // It is modified (assigned to null) when the ExchangeOperator is closed.
+        // It doesn't have to be declared as volatile as the nullification of this variable doesn't have to be immediately visible to other threads.
+        // However since close can be called at any moment this variable has to be accessed in a safe way (avoiding "check-then-use").
+        private ExchangeSource exchangeSource;
         private final List<ExchangeSourceHandle> exchangeSourceHandles;
         private final LocalMemoryContext systemMemoryContext;
+        private volatile boolean closed;
 
         private SpoolingExchangeDataSource(
                 ExchangeSource exchangeSource,
                 List<ExchangeSourceHandle> exchangeSourceHandles,
                 LocalMemoryContext systemMemoryContext)
         {
+            // this assignment is expected to be followed by an assignment of a final field to ensure safe publication
             this.exchangeSource = requireNonNull(exchangeSource, "exchangeSource is null");
             this.exchangeSourceHandles = ImmutableList.copyOf(requireNonNull(exchangeSourceHandles, "exchangeSourceHandles is null"));
             this.systemMemoryContext = requireNonNull(systemMemoryContext, "systemMemoryContext is null");
@@ -476,20 +485,39 @@ private SpoolingExchangeDataSource(
         @Override
         public Slice pollPage()
         {
+            ExchangeSource exchangeSource = this.exchangeSource;
+            if (exchangeSource == null) {
+                return null;
+            }
+
             Slice data = exchangeSource.read();
             systemMemoryContext.setBytes(exchangeSource.getMemoryUsage());
+
+            // If the data source has been closed in a meantime reset memory usage back to 0
+            if (closed) {
+                systemMemoryContext.setBytes(0);
+            }
+
             return data;
         }
 
         @Override
         public boolean isFinished()
         {
+            ExchangeSource exchangeSource = this.exchangeSource;
+            if (exchangeSource == null) {
+                return true;
+            }
             return exchangeSource.isFinished();
         }
 
         @Override
         public ListenableFuture<Void> isBlocked()
         {
+            ExchangeSource exchangeSource = this.exchangeSource;
+            if (exchangeSource == null) {
+                return immediateVoidFuture();
+            }
             return toListenableFuture(exchangeSource.isBlocked());
         }
 
@@ -522,9 +550,22 @@ public OperatorInfo getInfo()
         }
 
         @Override
-        public void close()
+        public synchronized void close()
         {
-            exchangeSource.close();
+            if (closed) {
+                return;
+            }
+            closed = true;
+            try {
+                exchangeSource.close();
+            }
+            catch (RuntimeException e) {
+                log.warn(e, "error closing exchange source");
+            }
+            finally {
+                exchangeSource = null;
+                systemMemoryContext.setBytes(0);
+            }
         }
     }
 }