X-Git-Url: http://source.jalview.org/gitweb/?p=jalview.git;a=blobdiff_plain;f=src%2Fjalview%2Fbin%2FApplicationSingletonProvider.java;fp=src%2Fjalview%2Fbin%2FApplicationSingletonProvider.java;h=b64f40c6516457aa97b28d261224e29eaf57eb8e;hp=0000000000000000000000000000000000000000;hb=7d602d0e4b439e56af3e4551ed71f181a8025534;hpb=adcef27f5747b4e70e89a56c3735bc3afb8ce9bf

diff --git a/src/jalview/bin/ApplicationSingletonProvider.java b/src/jalview/bin/ApplicationSingletonProvider.java
new file mode 100644
index 0000000..b64f40c
--- /dev/null
+++ b/src/jalview/bin/ApplicationSingletonProvider.java
@@ -0,0 +1,163 @@
+/*
+ * Jalview - A Sequence Alignment Editor and Viewer ($$Version-Rel$$)
+ * Copyright (C) $$Year-Rel$$ The Jalview Authors
+ * 
+ * This file is part of Jalview.
+ * 
+ * Jalview is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License 
+ * as published by the Free Software Foundation, either version 3
+ * of the License, or (at your option) any later version.
+ *  
+ * Jalview is distributed in the hope that it will be useful, but 
+ * WITHOUT ANY WARRANTY; without even the implied warranty 
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR 
+ * PURPOSE.  See the GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with Jalview.  If not, see <http://www.gnu.org/licenses/>.
+ * The Jalview Authors are detailed in the 'AUTHORS' file.
+ */
+package jalview.bin;
+
+import jalview.util.Platform;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A class to hold singleton objects, whose scope (context) is
+ * <ul>
+ * <li>the Java runtime (JVM) when running as Java</li>
+ * <li>one 'applet', when running as JalviewJS</li>
+ * </ul>
+ * This allows separation of multiple JS applets running on the same browser
+ * page, each with their own 'singleton' instances.
+ * <p>
+ * Instance objects are held in a separate Map (keyed by Class) for each
+ * context. For Java, this is just a single static Map. For SwingJS, the map is
+ * stored as a field {@code _swingjsSingletons} of
+ * {@code Thread.currentThread.getThreadGroup()}, as a proxy for the applet.
+ * <p>
+ * Note that when an applet is stopped, its ThreadGroup is removed, allowing any
+ * singleton references to be garbage collected.
+ * 
+ * @author hansonr
+ */
+public class ApplicationSingletonProvider
+{
+  /**
+   * A tagging interface to mark classes whose singleton instances may be served
+   * by {@code ApplicationSingletonProvider}, giving a distinct instance per JS
+   * 'applet'.
+   * <p>
+   * A class whose singleton should have global scope (be shared across all
+   * applets on a page) should <em>not</em> use this mechanism, but just provide
+   * a single instance (class static member) in the normal way.
+   */
+  public interface ApplicationSingletonI
+  {
+  }
+  
+  /*
+   * Map used to hold singletons in JVM context
+   */
+  private static Map<Class<? extends ApplicationSingletonI>, ApplicationSingletonI> singletons = new HashMap<>();
+
+  /**
+   * private constructor for non-instantiable class
+   */
+  private ApplicationSingletonProvider()
+  {
+  }
+
+  /**
+   * Returns the singletons map for the current context (JVM for Java,
+   * ThreadGroup for JS), creating the map on the first request for each JS
+   * ThreadGroup
+   * 
+   * @return
+   */
+  private static Map<Class<? extends ApplicationSingletonI>, ApplicationSingletonI> getContextMap()
+  {
+    @SuppressWarnings("unused")
+    ThreadGroup g = (Platform.isJS()
+            ? Thread.currentThread().getThreadGroup()
+            : null);
+    Map<Class<? extends ApplicationSingletonI>, ApplicationSingletonI> map = singletons;
+    /** @j2sNative map = g._swingjsSingletons; */
+    if (map == null)
+    {
+      map = new HashMap<>();
+      /** @j2sNative g._swingjsSingletons = map; */
+    }
+
+    return map;
+  }
+
+  /**
+   * Answers the singleton instance of the given class for the current context
+   * (JVM or SwingJS 'applet'). If no instance yet exists, one is created, by
+   * calling the class's no-argument constructor. Answers null if any error
+   * occurs (or occurred previously for the same class).
+   * 
+   * @param c
+   * @return
+   */
+  public static ApplicationSingletonI getInstance(Class<? extends ApplicationSingletonI> c)
+  {
+    Map<Class<? extends ApplicationSingletonI>, ApplicationSingletonI> map = getContextMap();
+    if (map.containsKey(c))
+    {
+      /*
+       * singleton already created _or_ creation failed (null value stored)
+       */
+      return map.get(c);
+    }
+
+    /*
+     * create and save the singleton
+     */
+    ApplicationSingletonI o = map.get(c);
+    try
+    {
+      Constructor<? extends ApplicationSingletonI> con = c
+              .getDeclaredConstructor();
+      con.setAccessible(true);
+      o = con.newInstance();
+    } catch (IllegalAccessException | InstantiationException
+            | IllegalArgumentException | InvocationTargetException
+            | NoSuchMethodException | SecurityException e)
+    {
+      Cache.log.error("Failed to create singleton for " + c.toString()
+              + ", error was: " + e.toString());
+      e.printStackTrace();
+    }
+
+    /*
+     * store the new singleton; note that a
+     * null value is saved if construction failed
+     */
+    getContextMap().put(c, o);
+    return o;
+  }
+
+  /**
+   * Removes the current singleton instance of the given class from the current
+   * application context. This has the effect of ensuring that a new instance is
+   * created the next time one is requested.
+   * 
+   * @param c
+   */
+  public static void removeInstance(
+          Class<? extends ApplicationSingletonI> c)
+  {
+    Map<Class<? extends ApplicationSingletonI>, ApplicationSingletonI> map = getContextMap();
+    if (map != null)
+    {
+      map.remove(c);
+    }
+  }
+}