8187443: Forest Consolidation: Move files to unified layout

Reviewed-by: darcy, ihse

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

@@ -0,0 +1,174 @@
+/*
+ * Copyright (c) 2007, 2013, 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.io.Closeable;
+import java.io.IOException;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * A watch service that <em>watches</em> registered objects for changes and
+ * events. For example a file manager may use a watch service to monitor a
+ * directory for changes so that it can update its display of the list of files
+ * when files are created or deleted.
+ *
+ * <p> A {@link Watchable} object is registered with a watch service by invoking
+ * its {@link Watchable#register register} method, returning a {@link WatchKey}
+ * to represent the registration. When an event for an object is detected the
+ * key is <em>signalled</em>, and if not currently signalled, it is queued to
+ * the watch service so that it can be retrieved by consumers that invoke the
+ * {@link #poll() poll} or {@link #take() take} methods to retrieve keys
+ * and process events. Once the events have been processed the consumer
+ * invokes the key's {@link WatchKey#reset reset} method to reset the key which
+ * allows the key to be signalled and re-queued with further events.
+ *
+ * <p> Registration with a watch service is cancelled by invoking the key's
+ * {@link WatchKey#cancel cancel} method. A key that is queued at the time that
+ * it is cancelled remains in the queue until it is retrieved. Depending on the
+ * object, a key may be cancelled automatically. For example, suppose a
+ * directory is watched and the watch service detects that it has been deleted
+ * or its file system is no longer accessible. When a key is cancelled in this
+ * manner it is signalled and queued, if not currently signalled. To ensure
+ * that the consumer is notified the return value from the {@code reset}
+ * method indicates if the key is valid.
+ *
+ * <p> A watch service is safe for use by multiple concurrent consumers. To
+ * ensure that only one consumer processes the events for a particular object at
+ * any time then care should be taken to ensure that the key's {@code reset}
+ * method is only invoked after its events have been processed. The {@link
+ * #close close} method may be invoked at any time to close the service causing
+ * any threads waiting to retrieve keys, to throw {@code
+ * ClosedWatchServiceException}.
+ *
+ * <p> File systems may report events faster than they can be retrieved or
+ * processed and an implementation may impose an unspecified limit on the number
+ * of events that it may accumulate. Where an implementation <em>knowingly</em>
+ * discards events then it arranges for the key's {@link WatchKey#pollEvents
+ * pollEvents} method to return an element with an event type of {@link
+ * StandardWatchEventKinds#OVERFLOW OVERFLOW}. This event can be used by the
+ * consumer as a trigger to re-examine the state of the object.
+ *
+ * <p> When an event is reported to indicate that a file in a watched directory
+ * has been modified then there is no guarantee that the program (or programs)
+ * that have modified the file have completed. Care should be taken to coordinate
+ * access with other programs that may be updating the file.
+ * The {@link java.nio.channels.FileChannel FileChannel} class defines methods
+ * to lock regions of a file against access by other programs.
+ *
+ * <h2>Platform dependencies</h2>
+ *
+ * <p> The implementation that observes events from the file system is intended
+ * to map directly on to the native file event notification facility where
+ * available, or to use a primitive mechanism, such as polling, when a native
+ * facility is not available. Consequently, many of the details on how events
+ * are detected, their timeliness, and whether their ordering is preserved are
+ * highly implementation specific. For example, when a file in a watched
+ * directory is modified then it may result in a single {@link
+ * StandardWatchEventKinds#ENTRY_MODIFY ENTRY_MODIFY} event in some
+ * implementations but several events in other implementations. Short-lived
+ * files (meaning files that are deleted very quickly after they are created)
+ * may not be detected by primitive implementations that periodically poll the
+ * file system to detect changes.
+ *
+ * <p> If a watched file is not located on a local storage device then it is
+ * implementation specific if changes to the file can be detected. In particular,
+ * it is not required that changes to files carried out on remote systems be
+ * detected.
+ *
+ * @since 1.7
+ *
+ * @see FileSystem#newWatchService
+ */
+
+public interface WatchService
+    extends Closeable
+{
+
+    /**
+     * Closes this watch service.
+     *
+     * <p> If a thread is currently blocked in the {@link #take take} or {@link
+     * #poll(long,TimeUnit) poll} methods waiting for a key to be queued then
+     * it immediately receives a {@link ClosedWatchServiceException}. Any
+     * valid keys associated with this watch service are {@link WatchKey#isValid
+     * invalidated}.
+     *
+     * <p> After a watch service is closed, any further attempt to invoke
+     * operations upon it will throw {@link ClosedWatchServiceException}.
+     * If this watch service is already closed then invoking this method
+     * has no effect.
+     *
+     * @throws  IOException
+     *          if an I/O error occurs
+     */
+    @Override
+    void close() throws IOException;
+
+    /**
+     * Retrieves and removes the next watch key, or {@code null} if none are
+     * present.
+     *
+     * @return  the next watch key, or {@code null}
+     *
+     * @throws  ClosedWatchServiceException
+     *          if this watch service is closed
+     */
+    WatchKey poll();
+
+    /**
+     * Retrieves and removes the next watch key, waiting if necessary up to the
+     * specified wait time if none are yet present.
+     *
+     * @param   timeout
+     *          how to wait before giving up, in units of unit
+     * @param   unit
+     *          a {@code TimeUnit} determining how to interpret the timeout
+     *          parameter
+     *
+     * @return  the next watch key, or {@code null}
+     *
+     * @throws  ClosedWatchServiceException
+     *          if this watch service is closed, or it is closed while waiting
+     *          for the next key
+     * @throws  InterruptedException
+     *          if interrupted while waiting
+     */
+    WatchKey poll(long timeout, TimeUnit unit)
+        throws InterruptedException;
+
+    /**
+     * Retrieves and removes next watch key, waiting if none are yet present.
+     *
+     * @return  the next watch key
+     *
+     * @throws  ClosedWatchServiceException
+     *          if this watch service is closed, or it is closed while waiting
+     *          for the next key
+     * @throws  InterruptedException
+     *          if interrupted while waiting
+     */
+    WatchKey take() throws InterruptedException;
+}