[hibernate#1909] Re-use existing connection during schema migration

hibernate-reactive-core/src/main/java/org/hibernate/reactive/provider/service/ReactiveImprovedExtractionContextImpl.java

@@ -36,6 +36,7 @@
 import java.util.Properties;
 import java.util.concurrent.CompletionStage;
 import java.util.concurrent.Executor;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import org.hibernate.boot.model.relational.SqlStringGenerationContext;
 import org.hibernate.engine.jdbc.env.spi.JdbcEnvironment;
@@ -53,6 +54,8 @@
 public class ReactiveImprovedExtractionContextImpl extends ImprovedExtractionContextImpl {
 
 	private final ReactiveConnectionPool service;
+	private final AtomicInteger level = new AtomicInteger( 0 );
+	private CompletionStage<ReactiveConnection> connectionStage;
 
 	public ReactiveImprovedExtractionContextImpl(
 			ServiceRegistry registry,
@@ -68,23 +71,35 @@ public ReactiveImprovedExtractionContextImpl(
 		service = registry.getService( ReactiveConnectionPool.class );
 	}
 
-	@Override
-	public <T> T getQueryResults(
-			String queryString,
-			Object[] positionalParameters,
-			ResultSetProcessor<T> resultSetProcessor) throws SQLException {
+	public ReactiveImprovedExtractionContextImpl push() {
+		int currentLevel = level.getAndIncrement();
+		if ( currentLevel == 0 ) {
+			connectionStage = service.getConnection();
+		}
+		return this;
+	}
 
-		final CompletionStage<ReactiveConnection> connectionStage = service.getConnection();
+	public ReactiveImprovedExtractionContextImpl pop() {
+		int currentLevel = level.decrementAndGet();
+		if ( currentLevel == 0 && connectionStage != null ) {
+			// This method doesn't return a reactive type, so we start closing the connection and ignore the result
+			connectionStage
+					.handle( ReactiveImprovedExtractionContextImpl::ignoreException )
+					.thenCompose( ReactiveImprovedExtractionContextImpl::closeConnection )
+					.toCompletableFuture()
+					.join();
+		}
+		return this;
+	}
 
+	@Override
+	public <T> T getQueryResults( String queryString, Object[] positionalParameters, ResultSetProcessor<T> resultSetProcessor) throws SQLException {
+		push();
 		try (final ResultSet resultSet = getQueryResultSet( queryString, positionalParameters, connectionStage )) {
 			return resultSetProcessor.process( resultSet );
 		}
 		finally {
-			// This method doesn't return a reactive type, so we start closing the connection and ignore the result
-			connectionStage
-					.handle( ReactiveImprovedExtractionContextImpl::ignoreException )
-					.thenCompose( ReactiveImprovedExtractionContextImpl::closeConnection );
-
+			pop();
 		}
 	}
 
@@ -102,13 +117,12 @@ private ResultSet getQueryResultSet(
 			Object[] positionalParameters,
 			CompletionStage<ReactiveConnection> connectionStage) {
 		final Object[] parametersToUse = positionalParameters != null ? positionalParameters : new Object[0];
-		final Parameters parametersDialectSpecific = Parameters.instance(
-				getJdbcEnvironment().getDialect()
-		);
+		final Parameters parametersDialectSpecific = Parameters.instance( getJdbcEnvironment().getDialect() );
 		final String queryToUse = parametersDialectSpecific.process( queryString, parametersToUse.length );
-		return connectionStage.thenCompose( c -> c.selectJdbcOutsideTransaction( queryToUse, parametersToUse ) )
+		return connectionStage
+				.thenCompose( c -> c.selectJdbcOutsideTransaction( queryToUse, parametersToUse ) )
 				.whenComplete( (resultSet, err) -> logSqlException( err, () -> "could not execute query ", queryToUse ) )
-				.thenApply(ResultSetWorkaround::new)
+				.thenApply( ResultSetWorkaround::new )
 				.toCompletableFuture()
 				.join();
 	}