Re: lock during update

["Eric Merritt" <cyberlync@xxxxxxxxx>]

Hey Glen, Your RPG Buddy is right the equaivilent of a RPG CHAIN is the
KeyedFile.read(), Basically when this happens the entire record should be
locked untile you either update the record or move the cursor off the
record.


 I f I were you i would take the statement

>        ControlFile.lock(KeyedFile.WRITE_ALLOW_SHARED_READ_LOCK);

Out of your code and let the 400 due the locking for you. Its less resource
intensive and safer to (in my opinion). We have been doing this type of
thing for over a year now with no problems.

Hope this helps.
----- Original Message -----
From: Glenn Holmer <gholmer@weycogroup.com>
To: Java400 mailing list <JAVA400-L@midrange.com>
Sent: Tuesday, November 21, 2000 5:27 PM
Subject: lock during update


> I have a Java class that wants to read a file to get the last used
> log number for the order file on an AS/400, increment it, then update
> it.  The code I was using was:
>
>        ControlFile.open(KeyedFile.READ_WRITE,
>                         0,  // blocking factor
>                         KeyedFile.COMMIT_LOCK_LEVEL_NONE);
>        ControlFile.lock(KeyedFile.WRITE_ALLOW_SHARED_READ_LOCK);
>
>        key = new Object[2];
>        key[0] = "LE"; key[1] = "          ";
>        rec = ControlFile.read(key);
>        ConfirmationNumber = (BigDecimal)rec.getField("CNVA2");
>        ConfirmationNumber = ConfirmationNumber.add(new BigDecimal("1"));
>        rec.setField("CNVA2", ConfirmationNumber);
>        ControlFile.update(key, rec);
>      } catch (Exception e) {
>        return (Object)e.getMessage();
>      } finally {
>        try {
>          ControlFile.releaseExplicitLocks();
>          ControlFile.close();
>
> But this fails when a background job kicks in that processes the orders
> that this same program writes, so it seems like "ControlFile.lock()" is
> excessive.  An RPG programmer in our shop tells me that when you update
> a record, that *record* is automatically locked.  But how do I ensure
> that no one changes the CNVA2 field out from under me between the time
> I read that record and the time I update it?  What the RPG programmer
> explained to me is that when you do a CHAIN, you either update the record
> or release it, but meantime it's yours.  What's the equivalent in Java?
> (Sorry if this isn't clear to AS/400 programmers, I'm mainly a PC guy.)
>
> --
> ____________________________________________________________
> Glenn Holmer                          gholmer@weycogroup.com
> Programmer/Analyst                       phone: 414.908.1809
> Weyco Group, Inc.                          fax: 414.908.1601
>
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