| /* |
| * Copyright (c) 2005, 2009, 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 sun.nio.ch; |
| |
| import java.nio.channels.*; |
| import java.util.*; |
| import java.util.concurrent.ConcurrentHashMap; |
| import java.lang.ref.*; |
| import java.io.FileDescriptor; |
| import java.io.IOException; |
| |
| abstract class FileLockTable { |
| protected FileLockTable() { |
| } |
| |
| /** |
| * Creates and returns a file lock table for a channel that is connected to |
| * the a system-wide map of all file locks for the Java virtual machine. |
| */ |
| public static FileLockTable newSharedFileLockTable(Channel channel, |
| FileDescriptor fd) |
| throws IOException |
| { |
| return new SharedFileLockTable(channel, fd); |
| } |
| |
| /** |
| * Adds a file lock to the table. |
| * |
| * @throws OverlappingFileLockException if the file lock overlaps |
| * with an existing file lock in the table |
| */ |
| public abstract void add(FileLock fl) throws OverlappingFileLockException; |
| |
| /** |
| * Remove an existing file lock from the table. |
| */ |
| public abstract void remove(FileLock fl); |
| |
| /** |
| * Removes all file locks from the table. |
| * |
| * @return The list of file locks removed |
| */ |
| public abstract List<FileLock> removeAll(); |
| |
| /** |
| * Replaces an existing file lock in the table. |
| */ |
| public abstract void replace(FileLock fl1, FileLock fl2); |
| } |
| |
| |
| /** |
| * A file lock table that is over a system-wide map of all file locks. |
| */ |
| class SharedFileLockTable extends FileLockTable { |
| |
| /** |
| * A weak reference to a FileLock. |
| * <p> |
| * SharedFileLockTable uses a list of file lock references to avoid keeping the |
| * FileLock (and FileChannel) alive. |
| */ |
| private static class FileLockReference extends WeakReference<FileLock> { |
| private FileKey fileKey; |
| |
| FileLockReference(FileLock referent, |
| ReferenceQueue<FileLock> queue, |
| FileKey key) { |
| super(referent, queue); |
| this.fileKey = key; |
| } |
| |
| FileKey fileKey() { |
| return fileKey; |
| } |
| } |
| |
| // The system-wide map is a ConcurrentHashMap that is keyed on the FileKey. |
| // The map value is a list of file locks represented by FileLockReferences. |
| // All access to the list must be synchronized on the list. |
| private static ConcurrentHashMap<FileKey, List<FileLockReference>> lockMap = |
| new ConcurrentHashMap<FileKey, List<FileLockReference>>(); |
| |
| // reference queue for cleared refs |
| private static ReferenceQueue<FileLock> queue = new ReferenceQueue<FileLock>(); |
| |
| // The connection to which this table is connected |
| private final Channel channel; |
| |
| // File key for the file that this channel is connected to |
| private final FileKey fileKey; |
| |
| SharedFileLockTable(Channel channel, FileDescriptor fd) throws IOException { |
| this.channel = channel; |
| this.fileKey = FileKey.create(fd); |
| } |
| |
| @Override |
| public void add(FileLock fl) throws OverlappingFileLockException { |
| List<FileLockReference> list = lockMap.get(fileKey); |
| |
| for (;;) { |
| |
| // The key isn't in the map so we try to create it atomically |
| if (list == null) { |
| list = new ArrayList<FileLockReference>(2); |
| List<FileLockReference> prev; |
| synchronized (list) { |
| prev = lockMap.putIfAbsent(fileKey, list); |
| if (prev == null) { |
| // we successfully created the key so we add the file lock |
| list.add(new FileLockReference(fl, queue, fileKey)); |
| break; |
| } |
| } |
| // someone else got there first |
| list = prev; |
| } |
| |
| // There is already a key. It is possible that some other thread |
| // is removing it so we re-fetch the value from the map. If it |
| // hasn't changed then we check the list for overlapping locks |
| // and add the new lock to the list. |
| synchronized (list) { |
| List<FileLockReference> current = lockMap.get(fileKey); |
| if (list == current) { |
| checkList(list, fl.position(), fl.size()); |
| list.add(new FileLockReference(fl, queue, fileKey)); |
| break; |
| } |
| list = current; |
| } |
| |
| } |
| |
| // process any stale entries pending in the reference queue |
| removeStaleEntries(); |
| } |
| |
| private void removeKeyIfEmpty(FileKey fk, List<FileLockReference> list) { |
| assert Thread.holdsLock(list); |
| assert lockMap.get(fk) == list; |
| if (list.isEmpty()) { |
| lockMap.remove(fk); |
| } |
| } |
| |
| @Override |
| public void remove(FileLock fl) { |
| assert fl != null; |
| |
| // the lock must exist so the list of locks must be present |
| List<FileLockReference> list = lockMap.get(fileKey); |
| if (list == null) return; |
| |
| synchronized (list) { |
| int index = 0; |
| while (index < list.size()) { |
| FileLockReference ref = list.get(index); |
| FileLock lock = ref.get(); |
| if (lock == fl) { |
| assert (lock != null) && (lock.acquiredBy() == channel); |
| ref.clear(); |
| list.remove(index); |
| break; |
| } |
| index++; |
| } |
| } |
| } |
| |
| @Override |
| public List<FileLock> removeAll() { |
| List<FileLock> result = new ArrayList<FileLock>(); |
| List<FileLockReference> list = lockMap.get(fileKey); |
| if (list != null) { |
| synchronized (list) { |
| int index = 0; |
| while (index < list.size()) { |
| FileLockReference ref = list.get(index); |
| FileLock lock = ref.get(); |
| |
| // remove locks obtained by this channel |
| if (lock != null && lock.acquiredBy() == channel) { |
| // remove the lock from the list |
| ref.clear(); |
| list.remove(index); |
| |
| // add to result |
| result.add(lock); |
| } else { |
| index++; |
| } |
| } |
| |
| // once the lock list is empty we remove it from the map |
| removeKeyIfEmpty(fileKey, list); |
| } |
| } |
| return result; |
| } |
| |
| @Override |
| public void replace(FileLock fromLock, FileLock toLock) { |
| // the lock must exist so there must be a list |
| List<FileLockReference> list = lockMap.get(fileKey); |
| assert list != null; |
| |
| synchronized (list) { |
| for (int index=0; index<list.size(); index++) { |
| FileLockReference ref = list.get(index); |
| FileLock lock = ref.get(); |
| if (lock == fromLock) { |
| ref.clear(); |
| list.set(index, new FileLockReference(toLock, queue, fileKey)); |
| break; |
| } |
| } |
| } |
| } |
| |
| // Check for overlapping file locks |
| private void checkList(List<FileLockReference> list, long position, long size) |
| throws OverlappingFileLockException |
| { |
| assert Thread.holdsLock(list); |
| for (FileLockReference ref: list) { |
| FileLock fl = ref.get(); |
| if (fl != null && fl.overlaps(position, size)) |
| throw new OverlappingFileLockException(); |
| } |
| } |
| |
| // Process the reference queue |
| private void removeStaleEntries() { |
| FileLockReference ref; |
| while ((ref = (FileLockReference)queue.poll()) != null) { |
| FileKey fk = ref.fileKey(); |
| List<FileLockReference> list = lockMap.get(fk); |
| if (list != null) { |
| synchronized (list) { |
| list.remove(ref); |
| removeKeyIfEmpty(fk, list); |
| } |
| } |
| } |
| } |
| } |