| /* | |
| * Copyright (c) 2005, 2023, 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.io.FileDescriptor; | |
| import java.io.IOException; | |
| import java.lang.ref.ReferenceQueue; | |
| import java.lang.ref.WeakReference; | |
| import java.nio.channels.Channel; | |
| import java.nio.channels.FileLock; | |
| import java.nio.channels.OverlappingFileLockException; | |
| import java.util.ArrayList; | |
| import java.util.HashSet; | |
| import java.util.List; | |
| import java.util.Set; | |
| import java.util.concurrent.ConcurrentHashMap; | |
| /** | |
| * A file lock table that is over a system-wide map of all file locks. | |
| */ | |
| class FileLockTable { | |
| /** | |
| * A weak reference to a FileLock. | |
| * <p> | |
| * FileLockTable uses a list of file lock references to avoid keeping the | |
| * FileLock (and FileChannel) alive. | |
| */ | |
| private static class FileLockReference extends WeakReference<FileLock> { | |
| private final 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 final ConcurrentHashMap<FileKey, List<FileLockReference>> lockMap = | |
| new ConcurrentHashMap<>(); | |
| // reference queue for cleared refs | |
| private static final ReferenceQueue<FileLock> queue = new ReferenceQueue<>(); | |
| // 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; | |
| // Locks obtained for this channel | |
| private final Set<FileLock> locks; | |
| /** | |
| * Creates a file lock table for a channel that is connected to the | |
| * system-wide map of all file locks for the Java virtual machine. | |
| */ | |
| FileLockTable(Channel channel, FileDescriptor fd) throws IOException { | |
| this.channel = channel; | |
| this.fileKey = FileKey.create(fd); | |
| this.locks = new HashSet<FileLock>(); | |
| } | |
| 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)); | |
| locks.add(fl); | |
| 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)); | |
| locks.add(fl); | |
| 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); | |
| } | |
| } | |
| 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); | |
| locks.remove(fl); | |
| break; | |
| } | |
| index++; | |
| } | |
| } | |
| } | |
| 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); | |
| locks.clear(); | |
| } | |
| } | |
| return result; | |
| } | |
| 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)); | |
| locks.remove(fromLock); | |
| locks.add(toLock); | |
| 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); | |
| } | |
| } | |
| } | |
| } | |
| } |