8187443: Forest Consolidation: Move files to unified layout

Reviewed-by: darcy, ihse

src/java.base/share/classes/java/nio/file/WatchKey.java

@@ -0,0 +1,150 @@
+/*
+ * Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code 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
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.nio.file;
+
+import java.util.List;
+
+/**
+ * A token representing the registration of a {@link Watchable watchable} object
+ * with a {@link WatchService}.
+ *
+ * <p> A watch key is created when a watchable object is registered with a watch
+ * service. The key remains {@link #isValid valid} until:
+ * <ol>
+ *   <li> It is cancelled, explicitly, by invoking its {@link #cancel cancel}
+ *     method, or</li>
+ *   <li> Cancelled implicitly, because the object is no longer accessible,
+ *     or </li>
+ *   <li> By {@link WatchService#close closing} the watch service. </li>
+ * </ol>
+ *
+ * <p> A watch key has a state. When initially created the key is said to be
+ * <em>ready</em>. When an event is detected then the key is <em>signalled</em>
+ * and queued so that it can be retrieved by invoking the watch service's {@link
+ * WatchService#poll() poll} or {@link WatchService#take() take} methods. Once
+ * signalled, a key remains in this state until its {@link #reset reset} method
+ * is invoked to return the key to the ready state. Events detected while the
+ * key is in the signalled state are queued but do not cause the key to be
+ * re-queued for retrieval from the watch service. Events are retrieved by
+ * invoking the key's {@link #pollEvents pollEvents} method. This method
+ * retrieves and removes all events accumulated for the object. When initially
+ * created, a watch key has no pending events. Typically events are retrieved
+ * when the key is in the signalled state leading to the following idiom:
+ *
+ * <pre>
+ *     for (;;) {
+ *         // retrieve key
+ *         WatchKey key = watcher.take();
+ *
+ *         // process events
+ *         for (WatchEvent&lt;?&gt; event: key.pollEvents()) {
+ *             :
+ *         }
+ *
+ *         // reset the key
+ *         boolean valid = key.reset();
+ *         if (!valid) {
+ *             // object no longer registered
+ *         }
+ *     }
+ * </pre>
+ *
+ * <p> Watch keys are safe for use by multiple concurrent threads. Where there
+ * are several threads retrieving signalled keys from a watch service then care
+ * should be taken to ensure that the {@code reset} method is only invoked after
+ * the events for the object have been processed. This ensures that one thread
+ * is processing the events for an object at any time.
+ *
+ * @since 1.7
+ */
+
+public interface WatchKey {
+
+    /**
+     * Tells whether or not this watch key is valid.
+     *
+     * <p> A watch key is valid upon creation and remains until it is cancelled,
+     * or its watch service is closed.
+     *
+     * @return  {@code true} if, and only if, this watch key is valid
+     */
+    boolean isValid();
+
+    /**
+     * Retrieves and removes all pending events for this watch key, returning
+     * a {@code List} of the events that were retrieved.
+     *
+     * <p> Note that this method does not wait if there are no events pending.
+     *
+     * @return  the list of the events retrieved; may be empty
+     */
+    List<WatchEvent<?>> pollEvents();
+
+    /**
+     * Resets this watch key.
+     *
+     * <p> If this watch key has been cancelled or this watch key is already in
+     * the ready state then invoking this method has no effect. Otherwise
+     * if there are pending events for the object then this watch key is
+     * immediately re-queued to the watch service. If there are no pending
+     * events then the watch key is put into the ready state and will remain in
+     * that state until an event is detected or the watch key is cancelled.
+     *
+     * @return  {@code true} if the watch key is valid and has been reset, and
+     *          {@code false} if the watch key could not be reset because it is
+     *          no longer {@link #isValid valid}
+     */
+    boolean reset();
+
+    /**
+     * Cancels the registration with the watch service. Upon return the watch key
+     * will be invalid. If the watch key is enqueued, waiting to be retrieved
+     * from the watch service, then it will remain in the queue until it is
+     * removed. Pending events, if any, remain pending and may be retrieved by
+     * invoking the {@link #pollEvents pollEvents} method after the key is
+     * cancelled.
+     *
+     * <p> If this watch key has already been cancelled then invoking this
+     * method has no effect.  Once cancelled, a watch key remains forever invalid.
+     */
+    void cancel();
+
+    /**
+     * Returns the object for which this watch key was created. This method will
+     * continue to return the object even after the key is cancelled.
+     *
+     * <p> As the {@code WatchService} is intended to map directly on to the
+     * native file event notification facility (where available) then many of
+     * details on how registered objects are watched is highly implementation
+     * specific. When watching a directory for changes for example, and the
+     * directory is moved or renamed in the file system, there is no guarantee
+     * that the watch key will be cancelled and so the object returned by this
+     * method may no longer be a valid path to the directory.
+     *
+     * @return the object for which this watch key was created
+     */
+    Watchable watchable();
+}