GH-3572 allow concurrent reads and writes against the WeakObjectRegistry

Signed-off-by: Håvard Ottestad <hmottestad@gmail.com>

core/rio/turtle/src/main/java/org/eclipse/rdf4j/rio/turtle/TurtleParser.java

@@ -278,12 +278,11 @@ protected void parsePrefixID() throws IOException, RDFParseException, RDFHandler
 		skipWSC();
 
 		// Read the namespace URI
-		IRI namespace = parseURI();
+		String namespaceStr = parseURI().toString();
 
-		// Store and report this namespace mapping
 		String prefixStr = prefixID.toString();
-		String namespaceStr = namespace.toString();
 
+		// Store and report this namespace mapping
 		setNamespace(prefixStr, namespaceStr);
 
 		if (rdfHandler != null) {

core/sail/memory/src/main/java/org/eclipse/rdf4j/sail/memory/MemorySailStore.java

@@ -40,6 +40,8 @@
 import org.eclipse.rdf4j.sail.base.SailSink;
 import org.eclipse.rdf4j.sail.base.SailSource;
 import org.eclipse.rdf4j.sail.base.SailStore;
+import org.eclipse.rdf4j.sail.memory.model.CloseableIterator;
+import org.eclipse.rdf4j.sail.memory.model.MemBNode;
 import org.eclipse.rdf4j.sail.memory.model.MemIRI;
 import org.eclipse.rdf4j.sail.memory.model.MemResource;
 import org.eclipse.rdf4j.sail.memory.model.MemStatement;
@@ -782,20 +784,25 @@ public CloseableIteration<? extends Resource, SailException> getContextIDs() thr
 
 			Lock stLock = openStatementsReadLock();
 			try {
-				synchronized (valueFactory) {
-					int snapshot = getCurrentSnapshot();
-					for (MemResource memResource : valueFactory.getMemURIs()) {
+				int snapshot = getCurrentSnapshot();
+				try (CloseableIterator<MemIRI> memIRIsIterator = valueFactory.getMemIRIsIterator()) {
+					while (memIRIsIterator.hasNext()) {
+						MemResource memResource = memIRIsIterator.next();
 						if (isContextResource(memResource, snapshot)) {
 							contextIDs.add(memResource);
 						}
 					}
+				}
 
-					for (MemResource memResource : valueFactory.getMemBNodes()) {
+				try (CloseableIterator<MemBNode> memBNodesIterator = valueFactory.getMemBNodesIterator()) {
+					while (memBNodesIterator.hasNext()) {
+						MemResource memResource = memBNodesIterator.next();
 						if (isContextResource(memResource, snapshot)) {
 							contextIDs.add(memResource);
 						}
 					}
 				}
+
 			} finally {
 				stLock.release();
 			}

core/sail/memory/src/main/java/org/eclipse/rdf4j/sail/memory/model/CloseableIterator.java

@@ -0,0 +1,17 @@
+/*******************************************************************************
+ * Copyright (c) 2022 Eclipse RDF4J contributors.
+ *  All rights reserved. This program and the accompanying materials
+ *  are made available under the terms of the Eclipse Distribution License v1.0
+ *  which accompanies this distribution, and is available at
+ *  http://www.eclipse.org/org/documents/edl-v10.php.
+ ******************************************************************************/
+
+package org.eclipse.rdf4j.sail.memory.model;
+
+import java.util.Iterator;
+
+public interface CloseableIterator<E> extends Iterator<E>, AutoCloseable {
+
+	@Override
+	void close();
+}