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| 1 | +/* | |
| 2 | + * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved. | |
| 3 | + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
| 4 | + * | |
| 5 | + * This code is free software; you can redistribute it and/or modify it | |
| 6 | + * under the terms of the GNU General Public License version 2 only, as | |
| 7 | + * published by the Free Software Foundation. Oracle designates this | |
| 8 | + * particular file as subject to the "Classpath" exception as provided | |
| 9 | + * by Oracle in the LICENSE file that accompanied this code. | |
| 10 | + * | |
| 11 | + * This code is distributed in the hope that it will be useful, but WITHOUT | |
| 12 | + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 13 | + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 14 | + * version 2 for more details (a copy is included in the LICENSE file that | |
| 15 | + * accompanied this code). | |
| 16 | + * | |
| 17 | + * You should have received a copy of the GNU General Public License version | |
| 18 | + * 2 along with this work; if not, write to the Free Software Foundation, | |
| 19 | + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
| 20 | + * | |
| 21 | + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 22 | + * or visit www.oracle.com if you need additional information or have any | |
| 23 | + * questions. | |
| 24 | + */ | |
| 25 | + | |
| 26 | +package java.awt; | |
| 27 | + | |
| 28 | +/** | |
| 29 | + * A helper interface to run the nested event loop. | |
| 30 | + * <p> | |
| 31 | + * Objects that implement this interface are created with the | |
| 32 | + * {@link EventQueue#createSecondaryLoop} method. The interface | |
| 33 | + * provides two methods, {@link #enter} and {@link #exit}, | |
| 34 | + * which can be used to start and stop the event loop. | |
| 35 | + * <p> | |
| 36 | + * When the {@link #enter} method is called, the current | |
| 37 | + * thread is blocked until the loop is terminated by the | |
| 38 | + * {@link #exit} method. Also, a new event loop is started | |
| 39 | + * on the event dispatch thread, which may or may not be | |
| 40 | + * the current thread. The loop can be terminated on any | |
| 41 | + * thread by calling its {@link #exit} method. After the | |
| 42 | + * loop is terminated, the {@code SecondaryLoop} object can | |
| 43 | + * be reused to run a new nested event loop. | |
| 44 | + * <p> | |
| 45 | + * A typical use case of applying this interface is AWT | |
| 46 | + * and Swing modal dialogs. When a modal dialog is shown on | |
| 47 | + * the event dispatch thread, it enters a new secondary loop. | |
| 48 | + * Later, when the dialog is hidden or disposed, it exits | |
| 49 | + * the loop, and the thread continues its execution. | |
| 50 | + * <p> | |
| 51 | + * The following example illustrates a simple use case of | |
| 52 | + * secondary loops: | |
| 53 | + * | |
| 54 | + * <pre> | |
| 55 | + * SecondaryLoop loop; | |
| 56 | + * | |
| 57 | + * JButton jButton = new JButton("Button"); | |
| 58 | + * jButton.addActionListener(new ActionListener() { | |
| 59 | + * {@code @Override} | |
| 60 | + * public void actionPerformed(ActionEvent e) { | |
| 61 | + * Toolkit tk = Toolkit.getDefaultToolkit(); | |
| 62 | + * EventQueue eq = tk.getSystemEventQueue(); | |
| 63 | + * loop = eq.createSecondaryLoop(); | |
| 64 | + * | |
| 65 | + * // Spawn a new thread to do the work | |
| 66 | + * Thread worker = new WorkerThread(); | |
| 67 | + * worker.start(); | |
| 68 | + * | |
| 69 | + * // Enter the loop to block the current event | |
| 70 | + * // handler, but leave UI responsive | |
| 71 | + * if (!loop.enter()) { | |
| 72 | + * // Report an error | |
| 73 | + * } | |
| 74 | + * } | |
| 75 | + * }); | |
| 76 | + * | |
| 77 | + * class WorkerThread extends Thread { | |
| 78 | + * {@code @Override} | |
| 79 | + * public void run() { | |
| 80 | + * // Perform calculations | |
| 81 | + * doSomethingUseful(); | |
| 82 | + * | |
| 83 | + * // Exit the loop | |
| 84 | + * loop.exit(); | |
| 85 | + * } | |
| 86 | + * } | |
| 87 | + * </pre> | |
| 88 | + * | |
| 89 | + * @see Dialog#show | |
| 90 | + * @see EventQueue#createSecondaryLoop | |
| 91 | + * @see Toolkit#getSystemEventQueue | |
| 92 | + * | |
| 93 | + * @author Anton Tarasov, Artem Ananiev | |
| 94 | + * | |
| 95 | + * @since 1.7 | |
| 96 | + */ | |
| 97 | +public interface SecondaryLoop { | |
| 98 | + | |
| 99 | + /** | |
| 100 | + * Blocks the execution of the current thread and enters a new | |
| 101 | + * secondary event loop on the event dispatch thread. | |
| 102 | + * <p> | |
| 103 | + * This method can be called by any thread including the event | |
| 104 | + * dispatch thread. This thread will be blocked until the {@link | |
| 105 | + * #exit} method is called or the loop is terminated. A new | |
| 106 | + * secondary loop will be created on the event dispatch thread | |
| 107 | + * for dispatching events in either case. | |
| 108 | + * <p> | |
| 109 | + * This method can only start one new event loop at a time per | |
| 110 | + * object. If a secondary event loop has already been started | |
| 111 | + * by this object and is currently still running, this method | |
| 112 | + * returns {@code false} to indicate that it was not successful | |
| 113 | + * in starting a new event loop. Otherwise, this method blocks | |
| 114 | + * the calling thread and later returns {@code true} when the | |
| 115 | + * new event loop is terminated. At such time, this object can | |
| 116 | + * again be used to start another new event loop. | |
| 117 | + * | |
| 118 | + * @return {@code true} after termination of the secondary loop, | |
| 119 | + * if the secondary loop was started by this call, | |
| 120 | + * {@code false} otherwise | |
| 121 | + */ | |
| 122 | + public boolean enter(); | |
| 123 | + | |
| 124 | + /** | |
| 125 | + * Unblocks the execution of the thread blocked by the {@link | |
| 126 | + * #enter} method and exits the secondary loop. | |
| 127 | + * <p> | |
| 128 | + * This method resumes the thread that called the {@link #enter} | |
| 129 | + * method and exits the secondary loop that was created when | |
| 130 | + * the {@link #enter} method was invoked. | |
| 131 | + * <p> | |
| 132 | + * Note that if any other secondary loop is started while this | |
| 133 | + * loop is running, the blocked thread will not resume execution | |
| 134 | + * until the nested loop is terminated. | |
| 135 | + * <p> | |
| 136 | + * If this secondary loop has not been started with the {@link | |
| 137 | + * #enter} method, or this secondary loop has already finished | |
| 138 | + * with the {@link #exit} method, this method returns {@code | |
| 139 | + * false}, otherwise {@code true} is returned. | |
| 140 | + * | |
| 141 | + * @return {@code true} if this loop was previously started and | |
| 142 | + * has not yet been finished with the {@link #exit} method, | |
| 143 | + * {@code false} otherwise | |
| 144 | + */ | |
| 145 | + public boolean exit(); | |
| 146 | + | |
| 147 | +} | |