Use initialization-on-demand holder for OpEnv

gselzer · gselzer · commit 809f3ba90101 · 2024-02-16T13:57:55.000-06:00
diff --git a/scijava-ops-legacy/src/main/java/org/scijava/legacy/service/DefaultOpEnvironmentService.java b/scijava-ops-legacy/src/main/java/org/scijava/legacy/service/DefaultOpEnvironmentService.java
@@ -1,7 +1,6 @@
 
 package org.scijava.legacy.service;
 
-import org.scijava.app.StatusService;
 import org.scijava.ops.api.OpEnvironment;
 import org.scijava.plugin.Attr;
 import org.scijava.plugin.Parameter;
@@ -14,7 +13,6 @@
 import org.scijava.service.Service;
 import org.scijava.task.TaskService;
 
-import java.io.ObjectInputFilter;
 import java.util.Map;
 import java.util.WeakHashMap;
 
@@ -34,13 +32,8 @@ public class DefaultOpEnvironmentService extends AbstractService implements
 	@Parameter(required = false)
 	private TaskService taskService;
 
-	private OpEnvironment env;
-
 	@Override
 	public void initialize() {
-		// Build the Op Environment
-		env = OpEnvironment.build();
-
 		// Set up alias, if ScriptService available
 		if (scriptService != null) {
 			scriptService.addAlias(OpEnvironment.class);
@@ -52,10 +45,10 @@ public void initialize() {
 		}
 	}
 
-	private class SciJavaProgressListener implements ProgressListener {
+	private static class SciJavaProgressListener implements ProgressListener {
 
 		private final Map<Task, org.scijava.task.Task> taskMap;
-		private TaskService tasks;
+		private final TaskService tasks;
 
 		public SciJavaProgressListener(TaskService tasks) {
 			this.tasks = tasks;
@@ -79,8 +72,22 @@ public void acknowledgeUpdate(Task task) {
 		}
 	}
 
+	/**
+	 * A class that lazily loads a static {@link OpEnvironment} using the <a
+	 * href=https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom>Initialization-on-demand
+	 * holder idiom</a>. This solution provides high concurrency, ensuring the
+	 * {@link OpEnvironment} is only constructed once.
+	 *
+	 * @author Gabriel Selzer
+	 */
+	private static class OpEnvironmentHolder {
+
+		public static final OpEnvironment env = OpEnvironment.build();
+	}
+
 	@Override
 	public OpEnvironment env() {
-		return env;
+		return OpEnvironmentHolder.env;
 	}
+
 }
