Add service for queuing startup operations

This will be useful for multiple reasons:

* The ImageJ Server's --server flag can now be combined with --headless
  to launch a blocking server, without --server blocking in UI mode.
* We may finally be able to fix imagej/imagej-legacy#89 by
  queuing the operation with the StartupService.

Author: ctrueden

pom.xml

@@ -10,7 +10,7 @@
 	</parent>
 
 	<artifactId>scijava-common</artifactId>
-	<version>2.70.2-SNAPSHOT</version>
+	<version>2.71.0-SNAPSHOT</version>
 
 	<name>SciJava Common</name>
 	<description>SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.</description>

src/main/java/org/scijava/AbstractGateway.java

@@ -58,6 +58,7 @@
 import org.scijava.prefs.PrefService;
 import org.scijava.script.ScriptService;
 import org.scijava.service.Service;
+import org.scijava.startup.StartupService;
 import org.scijava.text.TextService;
 import org.scijava.thread.ThreadService;
 import org.scijava.tool.IconService;
@@ -102,6 +103,9 @@ public void launch(final String... args) {
 		// NB: When running headless, the HeadlessUI will be used.
 		if (mainCount == 0) ui().showUI();
 
+		// perform all pending startup operations
+		startup().executeOperations();
+
 		if (ui().isHeadless()) {
 			// now that CLI processing/execution is done, we can shut down
 			getContext().dispose();
@@ -233,6 +237,11 @@ public ScriptService script() {
 		return get(ScriptService.class);
 	}
 
+	@Override
+	public StartupService startup() {
+		return get(StartupService.class);
+	}
+
 	@Override
 	public StatusService status() {
 		return get(StatusService.class);

src/main/java/org/scijava/Gateway.java

@@ -56,6 +56,7 @@
 import org.scijava.plugin.RichPlugin;
 import org.scijava.script.ScriptService;
 import org.scijava.service.Service;
+import org.scijava.startup.StartupService;
 import org.scijava.text.TextService;
 import org.scijava.thread.ThreadService;
 import org.scijava.tool.IconService;
@@ -311,6 +312,13 @@ public interface Gateway extends RichPlugin {
 	 */
 	ScriptService script();
 
+	/**
+	 * Gets this application context's {@link StartupService}.
+	 *
+	 * @return The {@link StartupService} of this application context.
+	 */
+	StartupService startup();
+
 	/**
 	 * Gets this application context's {@link StatusService}.
 	 *

src/main/java/org/scijava/startup/DefaultStartupService.java

@@ -0,0 +1,66 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2017 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, Max Planck
+ * Institute of Molecular Cell Biology and Genetics, University of
+ * Konstanz, and KNIME GmbH.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.startup;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+import org.scijava.plugin.Plugin;
+import org.scijava.service.AbstractService;
+import org.scijava.service.Service;
+
+/**
+ * Default implementation of {@link StartupService}.
+ * 
+ * @author Curtis Rueden
+ */
+@Plugin(type = Service.class)
+public class DefaultStartupService extends AbstractService implements
+	StartupService
+{
+
+	private final Deque<Runnable> operations = new ArrayDeque<>();
+
+	@Override
+	public void addOperation(final Runnable operation) {
+		operations.add(operation);
+	}
+
+	@Override
+	public void executeOperations() {
+		while (!operations.isEmpty()) {
+			final Runnable operation = operations.pop();
+			operation.run();
+		}
+	}
+}

src/main/java/org/scijava/startup/StartupService.java

@@ -0,0 +1,52 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2017 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, Max Planck
+ * Institute of Molecular Cell Biology and Genetics, University of
+ * Konstanz, and KNIME GmbH.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.startup;
+
+import org.scijava.service.SciJavaService;
+
+/**
+ * Interface for service managing startup operations.
+ * 
+ * @author Curtis Rueden
+ */
+public interface StartupService extends SciJavaService {
+
+	/** Adds an operation that will run as soon as the application starts up. */
+	void addOperation(Runnable r);
+
+	/**
+	 * Execute all registered startup operations, in the order they were
+	 * registered, blocking until complete.
+	 */
+	void executeOperations();
+}

src/test/java/org/scijava/ContextCreationTest.java

@@ -114,6 +114,7 @@ public void testFull() {
 				org.scijava.run.DefaultRunService.class,
 				org.scijava.script.DefaultScriptHeaderService.class,
 				org.scijava.script.process.DefaultScriptProcessorService.class,
+				org.scijava.startup.DefaultStartupService.class,
 				org.scijava.task.DefaultTaskService.class,
 				org.scijava.text.DefaultTextService.class,
 				org.scijava.thread.DefaultThreadService.class,