Examples of nexj.core.rpc.file.ra.LockableFile

nexj.core.rpc.file.ra.LockableFile
A thread-safe file lock implementation that works around deficiencies and unexpected behaviour in the Java file locking model. In particular, this class handles two problems: 1) Java's file locks are held at the process level, not at the thread level. If a thread requests a lock that is already held by the process, then an OverlappingFileLockException will be thrown (unless using Java version less than 6 and FileChannels are not the same). 2) Closing a channel *may* release all locks held by the JVM on the underlying file regardless of whether the locks were acquired via that channel or via another channel open on the same file. To fix #1, this class uses a locking queue so that when a thread locks a file that is already locked by another thread, that thread will block. To fix #2, this class keeps track of the files and channels that have been opened for locking, and ensures that the locks all share the same underlying channel, and that the channel is not closed until all locks have been released. Instances of this class are not safe for concurrent access from multiple threads. Instead, each thread should create an instance of this class on the same underlying file.

      {
         //Not found
         return new InstanceArrayList(0);
      }


      LockableFile directFile = new LockableFile(dataFile);


      //BLOCKING
      directFile.lock(true);
      
      try
      {
         Instance instance = m_context.findInstance(query.getMetaclass(), oid);


         if (instance == null)
         {
            instance = new Instance(query.getMetaclass(), m_context);
            instance.cache(oid);
         }


         for (Iterator i = query.getFieldIterator(); i.hasNext(); )
         {
            Field field = (Field)i.next();
            Attribute attribute = field.getAttribute();
            FilePrimitiveMapping primitiveMapping = (FilePrimitiveMapping)query.getPersistenceMapping().getAttributeMapping(attribute);
            
            switch (primitiveMapping.getSysId())
            {
               case FilePrimitiveMapping.SYSID_ID:
                  instance.setOldValueDirect(attribute.getOrdinal(), oid.getValue(0));
                  break;
                  
               case FilePrimitiveMapping.SYSID_DATA:
                  Object value = null;
                  
                  try
                  {
                     value = (primitiveMapping.getAttribute().getType() == Primitive.STRING) ?
                        (Object)directFile.getDataAsString() : directFile.getDataAsBinary();
                  }
                  catch (IOException ex)
                  {
                     throw new PersistenceException("err.persistence.file.io", ex);
                  }
                  
                  instance.setOldValueDirect(attribute.getOrdinal(), value);
                  
                  break;
               
               case FilePrimitiveMapping.SYSID_LOCKING:
                  instance.setOldValueDirect(attribute.getOrdinal(),
                     Primitive.createLong(dataFile.lastModified()) );
                  break;
            }
         }
         
         InstanceArrayList result = new InstanceArrayList(1);
         
         result.add(instance);
         
         return result;
      }
      finally
      {
         if (directFile != null)
         {
            directFile.unlock();
            directFile.close();
         }
      }
   }

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      }


      m_journalFile = new File(journalDirectory, JOURNAL_FILE1_NAME);
      m_compactionJournalFile = new File(journalDirectory, JOURNAL_FILE2_NAME);
      m_activeJournalPointerFile = new File(journalDirectory, JOURNAL_POINTER_FILE_NAME);
      m_journal = new LockableFile(m_journalFile);
      m_compactionJournal = new LockableFile(m_compactionJournalFile);


      boolean bReady = false;


      try
      {

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   /**
    * Swaps the handles 
    */
   protected void swapJournalFiles()
   {
      LockableFile handle;
      File file;
      
      handle = m_journal;
      m_journal = m_compactionJournal;
      m_compactionJournal = handle;

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