NX: URLyBird 1.1.3

[Max Habibi]

Originally posted by Vlad Rabkin:
Hi,
I've decided to dig into nio, but I synchronize read and write explicitly. I hope not to be penaltied for it.
Could anyone comment my code: It is my first attempt to do it- It works, but I am not sure the
the code is good (e.g. I don't if I should use force() method):

 public void write(int recNo, String[] data) throws IOException {
    DBColumnMetaData[] columns = fileMetaData_.getColumns();
    ByteBuffer bytes =
       ByteBuffer.allocate(fileMetaData_.getRecordLength());
     CharBuffer chars =
       CharBuffer.allocate(fileMetaData_.getRecordLength()-1);

    // write the first byte in the record indicating a valid record
    bytes.put(ACTIVE_RECORD);
    // write all fields in the record
    for (byte columnCounter = 0;
     columnCounter < fileMetaData_.getColumnsNumber();
     columnCounter++) {
      if (data[columnCounter] == null)
          data[columnCounter] = "";
      int space =
            columns[columnCounter].getLength() - data[columnCounter].length();
      // if length of the field from request is less than database defined,
      // fill the rest with blanks
      if (space > 0) {
        char[] cbuf = new char[space];
        Arrays.fill(cbuf, ' ');
        data[columnCounter] += new String(cbuf);
      } else
      if (space < 0)
       // if length of the field from request is greater than database defined,
       // throw an Exception
       throw
          new IllegalArgumentException(
                 "Database: <"
               + columns[columnCounter].getName()
               + "> field in request is too long");
       chars.put(data[columnCounter]);
     }
     chars.flip();
     charset.newEncoder().encode(chars, bytes, true);
     bytes.flip();
     fileChannel_.write(bytes, getFilePointer(recNo));
     fileChannel_.force(false);
} 

Regards,
Vlad

Hi Vlad,
It looks good, but I'd like to make a few suggestions/observation.
1. synchronize your write method. It's only the reads that are ok to leave unsynchronized.
2. close yout FileChannel when you're done with it, and null it out.
3. Nice, liberal use of comments. I like that
All best,
M

[Vlad Rabkin]

Hi Max,
First many thanx for your comments!
[Max]It looks good, but I'd like to make a few suggestions/observation.
1. synchronize your write method. It's only the reads that are ok to leave unsynchronized.
2. close yout FileChannel when you're done with it, and null it out.
3. Nice, liberal use of comments. I like that
1. It is private write method. It is used by main public method, which is synchronized on the map.
2. Max, as told: I will follow your idea to use FileChannel, but I will synchronize read explicitely and I will use shared FileChannel object, which I will not open and close every time. That means I guess I should not close it here. Considering what I have told here, should call force() method?
3) Thanx for the compliment!
Sorry for stupid questions, I am just trying to drive the car after reading instructions, but having no practise with the goal to get a driver license
Vlad

[Max Habibi]

I haven't heard you ask a stupid question, or make a stupid comment, yet Vlad. As to your question.

2. Max, as told: I will follow your idea to use FileChannel, but I will synchronize read explicitely and I will use shared FileChannel object, which I will not open and close every time. That means I guess I should not close it here. Considering what I have told here, should call force() method?

Yes, do use force, just for good measure. You shouldn't have to, but it doesn't hurt.
M

[Vlad Rabkin]

Hi Max,
Just to make sure I understand what I mean in �1:

     public void update(int recNo, String[] data, long lockCookie)
       throws RecordNotFoundException,
              SecurityException,
              DatabaseSystemException {
       synchronized (cashedDB_) {

        try {
          // check if the record exists. If no, throw an Exception
          checkRecord(recNo);
          checkAccess(recNo, lockCookie);
          checkArguments(data);
             // write the record
             write(recNo, data);
             cashedDB_.put(new Integer(recNo), data);
         } catch (IOException ioe) {
             throw new DatabaseSystemException(DB_EXEPTION, ioe);
         }
       }
     }  

Regards,
Vlad

[Max Habibi]

Looks fine. I'd probably do a notifyAll on cashedDB_ before exiting the synch block, but that's all.
Nice!
M

[Vlad Rabkin]

Max,

Many Thanx for your help!
Have a nice weekend.
Vlad

[Jim Yingst]

I've extracted a bunch of the posts that were specifically about FileChannel's "thread safety" and put them here. Please follow up that particular topic in that thread; other topics here. at the moment, all the original posts are still in this thread as well as having duplicates in the new thread. I'm inclinded to delete the duplicates from this thread, to clean things up, but others may feel their posts should be left here. So for the moment, I'm leaving this thread alone - but if no one objects I may delete the originals here for any posts that were copied to the other thread. Let me know if that seems undesireable...