Examples of java.nio.channels.FileLock

java.nio.channels.FileLock
A FileLock represents a locked region of a file.
Locks have certain properties that enable collaborating processes to avoid the lost update problem, or reading inconsistent data.

logically, a file lock can be 'exclusive' or 'shared'. Multiple processes can hold shared locks on the same region of a file, but only a single process can hold an exclusive lock on a given region of a file and no other process can simultaneously hold a shared lock overlapping the exclusive lock. An application can determine whether a FileLock is shared or exclusive via the isShared() API.

Locks held by a particular process cannot overlap one another. Applications can determine whether a proposed lock will overlap by using the overlaps(long, long)
Locks are shared amongst all threads in the acquiring process, and are therefore unsuitable for intra-process synchronization.
Once a lock is acquired it is immutable in all its state except isValid(). The lock will initially be valid, but may be rendered invalid by explicit removal of the lock, using release(), or implictly by closing the channel or exiting the process (terminating the JVM). Platform dependencies Locks are intended to be true platform operating system file locks, and therefore locks held by the JVM process will be visible to other OS processes. The characteristics of the underlying OS locks will show through in the Java implementation. For example, some platforms' locks are 'mandatory' -- meaning the operating system enforces the locks on processes that attempt to access locked regions of file; whereas other platforms' locks are only 'advisory' -- meaning that processes are required to collaborate on ensuring locks are acquired and there is a potential for processes not to play well. The only safe answer is to assume that the platform is adopting advisory locks an always acquire shared locks when reading a region of file. On some platforms the presence of a lock will prevent the file being memory mapped. On some platforms closing a channel on a given file handle will release all the locks held on that file -- even if there are other channels open on the same file (their locks will be released). The safe option here is to ensure that you only acquire locks on a single channel for a particular file, and that becomes the synchronization point. Further care should be exercised when locking files maintained on network file systems since they often have further limitations.




610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647 
                if (SqlJetLockType.SHARED.compareTo(this.lockType) < 0) {


                    if (SqlJetLockType.SHARED == lockType) {


                        final FileLock exclusiveLock = locks.get(SqlJetLockType.EXCLUSIVE);
                        if (null != exclusiveLock) {
                            if (exclusiveLock.isValid())
                                exclusiveLock.release();
                            locks.remove(SqlJetLockType.EXCLUSIVE);
                        }


                        if (null == locks.get(SqlJetLockType.SHARED)) {
                            final FileLock sharedLock = fileLockManager.lock(SHARED_FIRST, SHARED_SIZE, true);
                            if (null == sharedLock)
                                return false;
                            locks.put(SqlJetLockType.SHARED, sharedLock);
                            lockInfo.sharedLock = sharedLock;
                        }


                    }


                    final FileLock reservedLock = locks.get(SqlJetLockType.RESERVED);
                    if (null != reservedLock) {
                        if (reservedLock.isValid())
                            reservedLock.release();
                        locks.remove(SqlJetLockType.RESERVED);
                    }


                    final FileLock pendingLock = locks.get(SqlJetLockType.PENDING);
                    if (null != pendingLock) {
                        if (pendingLock.isValid())
                            pendingLock.release();
                        locks.remove(SqlJetLockType.PENDING);
                    }


                    lockInfo.lockType = SqlJetLockType.SHARED;


View Full Code Here





714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731                     return true;


                /* Otherwise see if some other process holds it. */
                try {


                    final FileLock reservedLock = fileLockManager.tryLock(RESERVED_BYTE, 1, false);


                    if (null == reservedLock) {
                        reserved = true;
                        return true;
                    }


                    reservedLock.release();


                } catch (IOException e) {
                }


            }
 

View Full Code Here


145
146
147
148
149
150
151
152
153
154
155         RandomAccessFile randomAccessFile = new RandomAccessFile(testFile,"rw");
        byte[] result = new byte[(int) randomAccessFile.length()];
        ByteBuffer buffer = ByteBuffer.wrap(result);
        try {
            randomAccessFile.getChannel().read(buffer, 0);
            FileLock fileLock = randomAccessFile.getChannel().tryLock(0,1,false);//read(buffer, 0);
            if(fileLock!=null){
                throw new IOException();
            }
        } catch (Exception e) {
            sessionContainer.close();

View Full Code Here


970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990    * storage directory. Otherwise, no guarantee is given.
   *
   * @throws IOException if locking fails
   */
  private void lock(File dir) throws IOException {
    FileLock lock = tryLock(dir);
    if (lock == null) {
      String msg = "Cannot lock " + dir
          + ". The directory is already locked. "
          + channelNameDescriptor;
      LOGGER.info(msg);
      throw new IOException(msg);
    }
    FileLock secondLock = tryLock(dir);
    if(secondLock != null) {
      LOGGER.warn("Directory "+dir+" does not support locking");
      secondLock.release();
      secondLock.channel().close();
    }
    locks.put(dir.getAbsolutePath(), lock);
  }
 

View Full Code Here


999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009   @SuppressWarnings("resource")
  private FileLock tryLock(File dir) throws IOException {
    File lockF = new File(dir, FILE_LOCK);
    lockF.deleteOnExit();
    RandomAccessFile file = new RandomAccessFile(lockF, "rws");
    FileLock res = null;
    try {
      res = file.getChannel().tryLock();
    } catch(OverlappingFileLockException oe) {
      file.close();
      return null;

View Full Code Here


1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031    * Unlock directory.
   *
   * @throws IOException
   */
  private void unlock(File dir) throws IOException {
    FileLock lock = locks.remove(dir.getAbsolutePath());
    if(lock == null) {
      return;
    }
    lock.release();
    lock.channel().close();
    lock = null;
  }
 

View Full Code Here


139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191                                                 FileOutputStream fos)
        throws IOException {
        
        // See if a file channel and lock can be obtained on the FileOutputStream
        FileChannel channel = null;
        FileLock lock = null;
        ByteBuffer bb = null;
        try {
            channel = fos.getChannel();
            if (channel != null) {
                lock = channel.tryLock();
            }
            bb = getTempByteBuffer();
        } catch (Throwable t) {
        }
        if (lock == null || bb == null || !bb.hasArray()) {
            releaseTempByteBuffer(bb);
            return false;  // lock could not be set or bb does not have direct array access
        }
        
        try {


            // Read directly into the ByteBuffer array
            int bytesRead = is.read(bb.array());
            while (bytesRead != -1) {
                int written = 0;
                
                
                if (bytesRead < BUFFER_LEN) {
                    // If the ByteBuffer is not full, allocate a new one
                    ByteBuffer temp = ByteBuffer.allocate(bytesRead);
                    temp.put(bb.array(), 0, bytesRead);
                    temp.position(0);
                    written = channel.write(temp);
                } else {
                    // Write to channel
                    bb.position(0);
                    written = channel.write(bb);
                    bb.clear();
                }
                
                // REVIEW: Do we need to ensure that bytesWritten is 
                // the same as the number of bytes sent ?
                
                bytesRead = is.read(bb.array());
            }
        } finally {
            // Release the lock
           lock.release();
           releaseTempByteBuffer(bb);
        }
        return true;
    }

View Full Code Here


1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128    * storage directory. Otherwise, no guarantee is given.
   *
   * @throws IOException if locking fails
   */
  private void lock(File dir) throws IOException {
    FileLock lock = tryLock(dir);
    if (lock == null) {
      String msg = "Cannot lock " + dir
          + ". The directory is already locked. "
          + channelNameDescriptor;
      LOGGER.info(msg);
      throw new IOException(msg);
    }
    FileLock secondLock = tryLock(dir);
    if(secondLock != null) {
      LOGGER.warn("Directory "+dir+" does not support locking");
      secondLock.release();
      secondLock.channel().close();
    }
    locks.put(dir.getAbsolutePath(), lock);
  }
 

View Full Code Here


1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147   @SuppressWarnings("resource")
  private FileLock tryLock(File dir) throws IOException {
    File lockF = new File(dir, FILE_LOCK);
    lockF.deleteOnExit();
    RandomAccessFile file = new RandomAccessFile(lockF, "rws");
    FileLock res = null;
    try {
      res = file.getChannel().tryLock();
    } catch(OverlappingFileLockException oe) {
      file.close();
      return null;

View Full Code Here


1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169    * Unlock directory.
   *
   * @throws IOException
   */
  private void unlock(File dir) throws IOException {
    FileLock lock = locks.remove(dir.getAbsolutePath());
    if(lock == null) {
      return;
    }
    lock.release();
    lock.channel().close();
    lock = null;
  }
 

View Full Code Here



0
1
2
3
4
5
6
7
8
9



TOP

Related Classes of java.nio.channels.FileLock

avrobase.file.FAB
ch.qos.logback.core.FileAppender
com.alibaba.dubbo.registry.support.AbstractRegistry
com.alibaba.rocketmq.store.index.IndexFile
com.asakusafw.runtime.util.lock.LocalFileLockProvider
com.asakusafw.windgate.file.session.FileSessionProvider
com.blogspot.mydailyjava.guava.cache.overflow.FileSystemPersistingCache
com.caucho.vfs.FileRandomAccessStream
com.caucho.vfs.FileReadStream
com.caucho.vfs.FileWriteStream



Copyright © 2018 www.massapicom. All rights reserved.
All source code are property of their respective owners. Java is a trademark of Sun Microsystems, Inc and owned by ORACLE Inc. Contact coftware#gmail.com.