Github user ajs6f commented on a diff in the pull request: https://github.com/apache/jena/pull/369#discussion_r172272325 --- Diff: jena-arq/src/main/java/org/apache/jena/sparql/core/TxnDataset2Graph.java --- @@ -0,0 +1,240 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.jena.sparql.core; + +import java.util.*; +import java.util.function.Consumer; + +import org.apache.jena.graph.Graph; +import org.apache.jena.graph.TransactionHandler; +import org.apache.jena.query.ReadWrite; +import org.apache.jena.query.TxnType; +import org.apache.jena.reasoner.InfGraph; +import org.apache.jena.shared.LockMRSW; +import org.apache.jena.sparql.JenaTransactionException; + +/** + * A {@link Transactional} that passes the transaction operations down to transactions on + * independent graphs. + * <p> + * There are limitations: + * <ul> + * <li>we can't atomically do all the commits together in the crash situation. + * <li>This {@code Transactional} maintains a MRSW policy because that is all that is + * required of graphs in general. + * </ul> + * It does cover the important case of one graph ({@link DatasetGraphOne}) where the one + * graph is an InfGraph and should work when the graphs in the dataset is not changing or + * when a new memory graph is added mid-transaction. + * <p> + * This is not "nested transactions" - theer is no overall "commit" or "abort". If + * failure/restart occurs, some graphs may have commited and others not. It is the best + * that can be done given for an arbitrary collection of graphs, backed by different + * storage and having different capabilities. + * <p> + * Best practice is to change the graph membership outside of any transaction, + * ideally at setup time of the object using this class. (Caution: SPARQL Update + * can create graphs. + * @See {@link DatasetGraphMapLink} + * @See {@link DatasetGraphOne} + */ +public class TxnDataset2Graph extends TransactionalLock { + /** + * Control whether to pass down transactions from the dataset to the graph in the + * dataset. This should be set to "true"; setting it "false" causes the onld, + * no-transaction passing behaviour. + * <p> + * This is temporary flag during the transition because the change at Jena 3.7.0 needs + * to be proven in real deployments as well as testing. "false" restores the Jena + * 3.6.0 and before behaviour (transactions not passed down). See JENA-1492. + * + * @deprecated This flag will be removed. + */ + @Deprecated + public static boolean TXN_DSG_GRAPH = true; + + private Graph primary; + // Object key may be a graph or a DSG is the graph is a GraphView. + // This avoids starting a tranasction on the same storage unit twice. + private Map<Object, TransactionHandler> handlers = new HashMap<>(); + + private Object lock = new Object(); + + public TxnDataset2Graph(Graph primaryGraph, Graph ... otherGraphs) { + super(new LockMRSW()); + primary = primaryGraph; + handlers = buildHandlerSet(primary, Arrays.asList(otherGraphs)); + } + + private static Map<Object, TransactionHandler> buildHandlerSet(Graph primary, Collection<Graph> graphs) { + Map<Object, TransactionHandler> handlers = new HashMap<>(); + addHandler(handlers, primary); + graphs.forEach(g->addHandler(handlers,g)); + return handlers; + } + + private static void addHandler(Map<Object, TransactionHandler> handlers, Graph graph) { + TransactionHandler th = graph.getTransactionHandler(); + if ( ! th.transactionsSupported() ) + return; + Object key = calcKey(graph); + if ( th.transactionsSupported() ) + handlers.put(key, th) ; + } + + // Determine the key - an object that is the unit of transactions. + // For two graphs form the same DatasetGraph, i.e. GraphView, there should be one transaction. + private static Object calcKey(Graph graph) { + if ( graph instanceof GraphView ) + // Use the database as the key so that transactions are started once-per-storage. + // This the case of a graph from some storage being plavced in a general dataset. + return ((GraphView)graph).getDataset(); + if ( graph instanceof InfGraph ) + // InfGraph does actual pass done in its TransactionHandler. + // This allows the base graph to be included in the dataset as well as the InfGraph. + return calcKey(((InfGraph)graph).getRawGraph()); + +// if ( graph instanceof GraphWrapper ) +// return calcKey(((GraphWrapper)graph).get()); +// if ( graph instanceof WrappedGraph ) +// return calcKey(((WrappedGraph)graph).getWrapped()); + return graph; + } + + private static void removeHandler(Map<Object, TransactionHandler> handlers, Graph graph) { + Object key = calcKey(graph); + handlers.remove(graph); + } + + // Attempt to manage the graph transactions during a transaction. + // Imperfect for removal, we don't know whether to call commit() or abort(). + // Works for adding. + // Generally better not to change the graphs during a transaction, just set them once + // on creation. + + public void addGraph(Graph graph) { + checkNotReadMode(); + if ( graph == null ) + return; + if ( ! handlers.containsKey(graph) ) { + // Add if new. + addHandler(handlers, graph) ; + if ( super.isInTransaction() ) { + // If we are in a transaction, start the subtransaction. + TransactionHandler th = handlers.get(graph); + if ( th != null ) + th.begin(); + } + } + } + + public void removeGraph(Graph graph) { + checkNotReadMode(); + if ( graph == null ) + return; + if ( ! super.isInTransaction() ) { + // Not in transaction, do now. + removeHandler(handlers, graph); + return; + } + // Queue to be removed at the end. + Set<Graph> toBeRemoved = removedGraphs.get(); + if ( toBeRemoved == null ) { + // Lazy set of the HashSet. + toBeRemoved = new HashSet<>(); + removedGraphs.set(toBeRemoved); + } + removedGraphs.get().add(graph); + } + + public void setPrimaryGraph(Graph graph) { + checkNotReadMode(); + if ( graph == null ) + return; + removeGraph(graph); + addGraph(graph); + } + + private void handlers(Consumer<TransactionHandler> action) { + synchronized (lock) { + handlers.forEach((g,th)->action.accept(th)); + } + } + + private void checkNotReadMode() { + if ( !super.isInTransaction() ) + return; + if ( super.isTransactionMode(ReadWrite.READ) ) + throw new JenaTransactionException("In READ mode in transaction"); + } + + private ThreadLocal<Set<Graph>> removedGraphs = ThreadLocal.withInitial(()->null); + private void start() {} + private void finish() { + if ( ! super.isTransactionMode(ReadWrite.WRITE) ) + return; + // This is called inside the lock of super. + Set<Graph> toBeRemoved = removedGraphs.get(); + removedGraphs.remove(); + if ( toBeRemoved == null ) + return ; + toBeRemoved.forEach(g->removeHandler(handlers, g)); + } + + // TransactionalLock.begin(ReadWrite) calls begin(TxnType) + @Override + public void begin(TxnType type) { + super.begin(type); + // Whatever the type. Graph Transactions do not allow for "read-only". + start(); + handlers(h->h.begin()); --- End diff -- It's fine not to, but what kind of IDE are you using that can't trace method references? Eclipse certainly can.
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