| /* |
| * Copyright (c) 2001, 2010, 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.channels; |
| |
| import java.io.IOException; |
| |
| /** |
| * A token representing a lock on a region of a file. |
| * |
| * <p> A file-lock object is created each time a lock is acquired on a file via |
| * one of the {@link FileChannel#lock(long,long,boolean) lock} or {@link |
| * FileChannel#tryLock(long,long,boolean) tryLock} methods of the |
| * {@link FileChannel} class |
| * |
| * <p> A file-lock object is initially valid. It remains valid until the lock |
| * is released by invoking the {@link #release release} method, by closing the |
| * channel that was used to acquire it, or by the termination of the Java |
| * virtual machine, whichever comes first. The validity of a lock may be |
| * tested by invoking its {@link #isValid isValid} method. |
| * |
| * <p> A file lock is either <i>exclusive</i> or <i>shared</i>. A shared lock |
| * prevents other concurrently-running programs from acquiring an overlapping |
| * exclusive lock, but does allow them to acquire overlapping shared locks. An |
| * exclusive lock prevents other programs from acquiring an overlapping lock of |
| * either type. Once it is released, a lock has no further effect on the locks |
| * that may be acquired by other programs. |
| * |
| * <p> Whether a lock is exclusive or shared may be determined by invoking its |
| * {@link #isShared isShared} method. Some platforms do not support shared |
| * locks, in which case a request for a shared lock is automatically converted |
| * into a request for an exclusive lock. |
| * |
| * <p> The locks held on a particular file by a single Java virtual machine do |
| * not overlap. The {@link #overlaps overlaps} method may be used to test |
| * whether a candidate lock range overlaps an existing lock. |
| * |
| * <p> A file-lock object records the file channel upon whose file the lock is |
| * held, the type and validity of the lock, and the position and size of the |
| * locked region. Only the validity of a lock is subject to change over time; |
| * all other aspects of a lock's state are immutable. |
| * |
| * <p> File locks are held on behalf of the entire Java virtual machine. |
| * They are not suitable for controlling access to a file by multiple |
| * threads within the same virtual machine. |
| * |
| * <p> File-lock objects are safe for use by multiple concurrent threads. |
| * |
| * |
| * <a name="pdep"><h4> Platform dependencies </h4></a> |
| * |
| * <p> This file-locking API is intended to map directly to the native locking |
| * facility of the underlying operating system. Thus the locks held on a file |
| * should be visible to all programs that have access to the file, regardless |
| * of the language in which those programs are written. |
| * |
| * <p> Whether or not a lock actually prevents another program from accessing |
| * the content of the locked region is system-dependent and therefore |
| * unspecified. The native file-locking facilities of some systems are merely |
| * <i>advisory</i>, meaning that programs must cooperatively observe a known |
| * locking protocol in order to guarantee data integrity. On other systems |
| * native file locks are <i>mandatory</i>, meaning that if one program locks a |
| * region of a file then other programs are actually prevented from accessing |
| * that region in a way that would violate the lock. On yet other systems, |
| * whether native file locks are advisory or mandatory is configurable on a |
| * per-file basis. To ensure consistent and correct behavior across platforms, |
| * it is strongly recommended that the locks provided by this API be used as if |
| * they were advisory locks. |
| * |
| * <p> On some systems, acquiring a mandatory lock on a region of a file |
| * prevents that region from being {@link java.nio.channels.FileChannel#map |
| * <i>mapped into memory</i>}, and vice versa. Programs that combine |
| * locking and mapping should be prepared for this combination to fail. |
| * |
| * <p> On some systems, closing a channel releases all locks held by the Java |
| * virtual machine on the underlying file regardless of whether the locks were |
| * acquired via that channel or via another channel open on the same file. It |
| * is strongly recommended that, within a program, a unique channel be used to |
| * acquire all locks on any given file. |
| * |
| * <p> Some network filesystems permit file locking to be used with |
| * memory-mapped files only when the locked regions are page-aligned and a |
| * whole multiple of the underlying hardware's page size. Some network |
| * filesystems do not implement file locks on regions that extend past a |
| * certain position, often 2<sup>30</sup> or 2<sup>31</sup>. In general, great |
| * care should be taken when locking files that reside on network filesystems. |
| * |
| * |
| * @author Mark Reinhold |
| * @author JSR-51 Expert Group |
| * @since 1.4 |
| */ |
| |
| public abstract class FileLock implements AutoCloseable { |
| |
| private final Channel channel; |
| private final long position; |
| private final long size; |
| private final boolean shared; |
| |
| /** |
| * Initializes a new instance of this class. </p> |
| * |
| * @param channel |
| * The file channel upon whose file this lock is held |
| * |
| * @param position |
| * The position within the file at which the locked region starts; |
| * must be non-negative |
| * |
| * @param size |
| * The size of the locked region; must be non-negative, and the sum |
| * <tt>position</tt> + <tt>size</tt> must be non-negative |
| * |
| * @param shared |
| * <tt>true</tt> if this lock is shared, |
| * <tt>false</tt> if it is exclusive |
| * |
| * @throws IllegalArgumentException |
| * If the preconditions on the parameters do not hold |
| */ |
| protected FileLock(FileChannel channel, |
| long position, long size, boolean shared) |
| { |
| if (position < 0) |
| throw new IllegalArgumentException("Negative position"); |
| if (size < 0) |
| throw new IllegalArgumentException("Negative size"); |
| if (position + size < 0) |
| throw new IllegalArgumentException("Negative position + size"); |
| this.channel = channel; |
| this.position = position; |
| this.size = size; |
| this.shared = shared; |
| } |
| |
| /** |
| * Returns the file channel upon whose file this lock was acquired. |
| * |
| * <p> This method has been superseded by the {@link #acquiredBy acquiredBy} |
| * method. |
| * |
| * @return The file channel, or {@code null} if the file lock was not |
| * acquired by a file channel. |
| */ |
| public final FileChannel channel() { |
| return (channel instanceof FileChannel) ? (FileChannel)channel : null; |
| } |
| |
| /** |
| * Returns the channel upon whose file this lock was acquired. |
| * |
| * @return The channel upon whose file this lock was acquired. |
| * |
| * @since 1.7 |
| */ |
| public Channel acquiredBy() { |
| return channel; |
| } |
| |
| /** |
| * Returns the position within the file of the first byte of the locked |
| * region. |
| * |
| * <p> A locked region need not be contained within, or even overlap, the |
| * actual underlying file, so the value returned by this method may exceed |
| * the file's current size. </p> |
| * |
| * @return The position |
| */ |
| public final long position() { |
| return position; |
| } |
| |
| /** |
| * Returns the size of the locked region in bytes. |
| * |
| * <p> A locked region need not be contained within, or even overlap, the |
| * actual underlying file, so the value returned by this method may exceed |
| * the file's current size. </p> |
| * |
| * @return The size of the locked region |
| */ |
| public final long size() { |
| return size; |
| } |
| |
| /** |
| * Tells whether this lock is shared. </p> |
| * |
| * @return <tt>true</tt> if lock is shared, |
| * <tt>false</tt> if it is exclusive |
| */ |
| public final boolean isShared() { |
| return shared; |
| } |
| |
| /** |
| * Tells whether or not this lock overlaps the given lock range. </p> |
| * |
| * @return <tt>true</tt> if, and only if, this lock and the given lock |
| * range overlap by at least one byte |
| */ |
| public final boolean overlaps(long position, long size) { |
| if (position + size <= this.position) |
| return false; // That is below this |
| if (this.position + this.size <= position) |
| return false; // This is below that |
| return true; |
| } |
| |
| /** |
| * Tells whether or not this lock is valid. |
| * |
| * <p> A lock object remains valid until it is released or the associated |
| * file channel is closed, whichever comes first. </p> |
| * |
| * @return <tt>true</tt> if, and only if, this lock is valid |
| */ |
| public abstract boolean isValid(); |
| |
| /** |
| * Releases this lock. |
| * |
| * <p> If this lock object is valid then invoking this method releases the |
| * lock and renders the object invalid. If this lock object is invalid |
| * then invoking this method has no effect. </p> |
| * |
| * @throws ClosedChannelException |
| * If the channel that was used to acquire this lock |
| * is no longer open |
| * |
| * @throws IOException |
| * If an I/O error occurs |
| */ |
| public abstract void release() throws IOException; |
| |
| /** |
| * This method invokes the {@link #release} method. It was added |
| * to the class so that it could be used in conjunction with the |
| * automatic resource management block construct. |
| * |
| * @since 1.7 |
| */ |
| public final void close() throws IOException { |
| release(); |
| } |
| |
| /** |
| * Returns a string describing the range, type, and validity of this lock. |
| * |
| * @return A descriptive string |
| */ |
| public final String toString() { |
| return (this.getClass().getName() |
| + "[" + position |
| + ":" + size |
| + " " + (shared ? "shared" : "exclusive") |
| + " " + (isValid() ? "valid" : "invalid") |
| + "]"); |
| } |
| |
| } |
