[CORE-653] Lock around restore call to reduce risk of conflict.

scg-system/src/main/java/io/telicent/backup/services/DatasetBackupService.java

@@ -22,6 +22,8 @@
 import io.telicent.jena.abac.labels.LabelsStore;
 import io.telicent.jena.abac.labels.LabelsStoreRocksDB;
 import io.telicent.jena.graphql.utils.ExcludeFromJacocoGeneratedReport;
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
 import org.apache.jena.atlas.lib.DateTimeUtils;
 import org.apache.jena.fuseki.mgt.Backup;
 import org.apache.jena.fuseki.server.DataAccessPoint;
@@ -37,13 +39,16 @@
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.zip.GZIPInputStream;
 
 import static io.telicent.backup.utils.BackupUtils.*;
 import static org.apache.jena.riot.Lang.NQUADS;
 
 public class DatasetBackupService {
 
+    private final ReentrantLock lock;
+
     private final DataAccessPointRegistry dapRegistry;
 
     final static ConcurrentHashMap<String, TriConsumer<DataAccessPoint, String, ObjectNode>> backupConsumerMap = new ConcurrentHashMap<>();
@@ -53,6 +58,39 @@ public DatasetBackupService(DataAccessPointRegistry dapRegistry) {
         this.dapRegistry = dapRegistry;
         registerMethods("tdb", this::backupTDB, this::restoreTDB);
         registerMethods("labels", this::backupLabelStore, this::restoreLabelStore);
+        lock = new ReentrantLock();
+    }
+
+    /**
+     * Ensures that only oine operation is processed at a time
+     * @param request incoming request
+     * @param response outgoing response
+     * @param backup flag indicating backup or restore
+     */
+    public void process(HttpServletRequest request, HttpServletResponse response, boolean backup) {
+        // Try to acquire the lock without blocking
+        ObjectNode resultNode = MAPPER.createObjectNode();
+        if (!lock.tryLock()) {
+            response.setStatus(HttpServletResponse.SC_CONFLICT);
+            resultNode.put("error", "Another conflicting operation is already in progress. Please try again later.");
+            processResponse(response, resultNode);
+        } else {
+            try {
+                String id = request.getPathInfo();
+                resultNode.put("id", id);
+                resultNode.put("date", DateTimeUtils.nowAsString("yyyy-MM-dd_HH-mm-ss"));
+                if (backup) {
+                    resultNode.set("backup", backupDataset(id));
+                } else {
+                    resultNode.set("restore", restoreDatasets(id));
+                }
+                processResponse(response, resultNode);
+            } catch (Exception exception) {
+                handleError(response, resultNode, exception);
+            } finally {
+                lock.unlock();
+            }
+        }
     }
 
     /**

scg-system/src/main/java/io/telicent/backup/servlets/BackupServlet.java

@@ -16,14 +16,10 @@
 
 package io.telicent.backup.servlets;
 
-import com.fasterxml.jackson.databind.node.ObjectNode;
 import io.telicent.backup.services.DatasetBackupService;
 import jakarta.servlet.http.HttpServlet;
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpServletResponse;
-import org.apache.jena.atlas.lib.DateTimeUtils;
-
-import static io.telicent.backup.utils.BackupUtils.*;
 
 /**
  * Servlet class responsible for the creation of backups.
@@ -37,15 +33,6 @@ public BackupServlet(DatasetBackupService backupService) {
 
     @Override
     protected void doPost(HttpServletRequest request, HttpServletResponse response) {
-        ObjectNode resultNode = MAPPER.createObjectNode();
-        try {
-            String datasetName = request.getPathInfo();
-            resultNode.put("dataset", datasetName);
-            resultNode.put("date", DateTimeUtils.nowAsString("yyyy-MM-dd_HH-mm-ss"));
-            resultNode.set("backup", backupService.backupDataset(datasetName));
-            processResponse(response, resultNode);
-        } catch (Exception exception) {
-            handleError(response, resultNode, exception);
-        }
+        backupService.process(request, response, true);
     }
 }

scg-system/src/main/java/io/telicent/backup/servlets/RestoreServlet.java

@@ -16,36 +16,22 @@
 
 package io.telicent.backup.servlets;
 
-import com.fasterxml.jackson.databind.node.ObjectNode;
 import io.telicent.backup.services.DatasetBackupService;
 import jakarta.servlet.http.HttpServlet;
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpServletResponse;
-import org.apache.jena.atlas.lib.DateTimeUtils;
-
-import static io.telicent.backup.utils.BackupUtils.*;
 
 /**
- * Servlet class responsible for the loading of given backup.
+ * Servlet class responsible for the loading of a given backup.
  */
 public class RestoreServlet extends HttpServlet {
     private final DatasetBackupService backupService;
-
     public RestoreServlet(DatasetBackupService backupService) {
         this.backupService = backupService;
     }
 
     @Override
     protected void doPost(HttpServletRequest request, HttpServletResponse response) {
-        ObjectNode resultNode = MAPPER.createObjectNode();
-        try {
-            String restoreId = request.getPathInfo();
-            resultNode.put("restore-id", restoreId);
-            resultNode.put("date", DateTimeUtils.nowAsString("yyyy-MM-dd_HH-mm-ss"));
-            resultNode.set("restore", backupService.restoreDatasets(restoreId));
-            processResponse(response, resultNode);
-        } catch (Exception exception) {
-            handleError(response, resultNode, exception);
-        }
+        backupService.process(request, response,false);
     }
 }

scg-system/src/test/java/io/telicent/backup/TestBackupData.java

@@ -44,13 +44,17 @@
 import static org.apache.jena.graph.Graph.emptyGraph;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.reset;
 
 public class TestBackupData {
 
     private static FusekiServer server;
 
     private FMod_BackupData testModule;
 
+    private static DatasetBackupService mockService = mock(DatasetBackupService.class);
+
     @BeforeEach
     public void createAndSetupServerDetails() throws Exception {
         LibTestsSCG.setupAuthentication();
@@ -68,6 +72,7 @@ void clearDown() throws Exception {
         }
         LibTestsSCG.teardownAuthentication();
         Configurator.reset();
+        reset(mockService);
     }
 
     private FusekiModules generateModulesAndReplaceWithTestModule() {
@@ -223,15 +228,23 @@ public void test_restoreBackup_error() {
      * @param response generated response
      */
     private void debug(HttpResponse<InputStream> response) {
+        System.out.println(convertToJSON(response));
+    }
+
+    /**
+     * Obtain the JSON String from the HTTP Response
+     * @param response the response returned
+     * @return a JSON string
+     */
+    private String convertToJSON(HttpResponse<InputStream> response) {
         try {
             InputStream inputStream = response.body();
             InputStreamReader reader = new InputStreamReader(inputStream);
             ObjectMapper mapper = new ObjectMapper();
             Object jsonObject = mapper.readValue(reader, Object.class);
-            String jsonString = mapper.writeValueAsString(jsonObject);
-            System.out.println(jsonString);
+            return mapper.writeValueAsString(jsonObject);
         }catch (IOException e) {
-            System.out.println(e.getMessage());
+            return e.getMessage();
         }
     }
 
@@ -258,4 +271,16 @@ DatasetBackupService getBackupService(DataAccessPointRegistry dapRegistry) {
             return null;
         }
     }
+
+    /**
+     * Extension of the Backup Module for testing purposes.
+     * Allows the underlying service to be mocked
+     */
+    public static class FMod_BackupData_Mock extends FMod_BackupData {
+
+        @Override
+        DatasetBackupService getBackupService(DataAccessPointRegistry dapRegistry) {
+            return mockService;
+        }
+    }
 }

scg-system/src/test/java/io/telicent/backup/services/TestDatasetBackupService.java

@@ -22,6 +22,9 @@
 import io.telicent.jena.abac.ABAC;
 import io.telicent.jena.abac.core.DatasetGraphABAC;
 import io.telicent.jena.abac.labels.LabelsStoreRocksDB;
+import jakarta.servlet.ServletOutputStream;
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
 import org.apache.jena.fuseki.server.DataAccessPoint;
 import org.apache.jena.fuseki.server.DataAccessPointRegistry;
 import org.apache.jena.fuseki.server.DataService;
@@ -35,14 +38,16 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
 
 import static io.telicent.backup.services.DatasetBackupService_Test.*;
 import static io.telicent.backup.utils.BackupUtils.MAPPER;
 import static java.util.Collections.emptyList;
 import static org.junit.jupiter.api.Assertions.*;
 import static org.mockito.ArgumentMatchers.anyString;
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.*;
 
 public class TestDatasetBackupService {
 
@@ -1020,6 +1025,34 @@ public void test_restoreLabelStore_wrongPath() {
         assertTrue(RESULT_NODE.get("reason").asText().startsWith("Restore directory not found: "));
     }
 
+    @Test
+    public void test_process_multipleCalls() throws InterruptedException, IOException {
+        HttpServletRequest request = mock(HttpServletRequest.class);
+        HttpServletResponse response = mock(HttpServletResponse.class);
+        ServletOutputStream outputStream = mock(ServletOutputStream.class);
+        when(response.getOutputStream()).thenReturn(outputStream);
+        doAnswer(invocation -> {
+            Thread.sleep(50); // Simulate  operation
+            return "dataset";
+        }).when(request).getPathInfo();
+
+        // Use ExecutorService to run multiple threads
+        try (ExecutorService executorService = Executors.newFixedThreadPool(2)) {
+
+            // Submit 5 concurrent tasks simulating individual requests
+            for (int i = 0; i < 2; i++) {
+                final boolean flag = (i == 0);
+                executorService.submit(() -> {
+                        cut.process(request, response, flag);
+                });
+            }
+            // Wait for threads to complete
+            executorService.shutdown();
+            executorService.awaitTermination(1, TimeUnit.SECONDS);
+        }
+        verify(response, times(1)).setStatus(409);
+    }
+
     public void doNothing(DataAccessPoint dataAccessPoint, String path, ObjectNode resultNode) {
         resultNode.put("success", true);
     }