On 2017-12-27 12:29, Claude Warren wrote:
> I recently wrote some code to try to handle a similar situation. In my
> case I knew I needed a transaction to be active at various points so I
> created a TransactionHolder. I create the holder and passing the object
> that has implements Transactional as well as the type of ReadWrite I want.
>
> If the transaction is active it does nothing (and I hope the proper
> transaction has been started) otherwise It starts the transaction.
> Ad the end I call commit or abort as appropriate. If I did not start the
> transaction the commit, abort or end is ignored.
I see the same problem in your code as I pointed out before. A
transaction behaves differently if it is READ or WRITE and in your code
there is not such a thing. Actually the isInTransaction() doesn't give
you this information.
Then nesting is not safe as you might have open initially a read
transaction and then include a write. If the parent one is a write there
shouldn't be such an issue (I guess).
Just for you to know, your code is more or less integrated in [1], so
you can "update" your code.
[1]: jena/jena-arq/src/main/java/org/apache/jena/system/Txn.java
> I think there may be an issue with abort in that it should probablyset up
> end() to throw an exception when I have not created the transaction so
> that the outer transaction will fail.
>
> import org.apache.jena.query.ReadWrite;
> import org.apache.jena.sparql.core.Transactional;
>
> public class TransactionHolder {
> private final Transactional txn;
> private final boolean started;
> private final ReadWrite rw;
>
> public TransactionHolder( Transactional txn, ReadWrite rw )
> {
> this.txn = txn;
> this.rw = rw;
> started = ! txn.isInTransaction();
> if (started)
> {
> txn.begin( rw );
> }
> }
>
> public boolean ownsTranaction() {
> return started;
> }
>
> public void commit() {
> if (started) {
> txn.commit();
> }
> }
>
> public void abort() {
> if (started)
> {
> txn.abort();
> }
> }
>
> public void end() {
> if (started) {
> txn.end();
> }
> }
>
> }
>
>
> On Wed, Dec 27, 2017 at 11:03 AM, dandh988 <[email protected]> wrote:
>
>> You cannot nest transactions nor can you promote a read to a write.
>> You need to rewrite your code or use txn which correctly checks if a
>> transaction is available and if not will begin the correct one, either READ
>> or WRITE.
>>
>>
>> Dick
>> -------- Original message --------From: George News <[email protected]>
>> Date: 27/12/2017 10:27 (GMT+00:00) To: Jena User Mailing List <
>> [email protected]> Subject: Txn code not handling type of transaction
>> Hi,
>>
>> As you know from other threads I'm having some issues with transactions.
>> Your suggestion is to use Txn instead of begin/end. Just for curiosity I
>> have checked the Txn code at [1] and it seems that inside you use
>> begin/end.
>>
>> However I have a doubt concerning how you handle the begin/end for READ
>> and WRITE. It seems that you open a transaction based on
>> txn.isInTransaction(), but how do you know if it is a READ or WRITE?
>>
>> If you create something like:
>>
>> Txn.executeRead(dataset, {
>> Txn.executeWrite(dataset, {
>> // Whatever
>> }
>> }
>> }
>>
>> the txn.begin(ReadWrite.WRITE) is not called and therefore it might be
>> leading to unexepected behaviours for the txn.commit().
>>
>> could you give some hints on how this is handle internally? Before fully
>> modify the code I have, it might be easier to replicate the txn
>> behaviour ;) but I would like to know the above (if possible).
>>
>> As always, thanks in advanced
>> Jorge
>>
>> [1]: jena/jena-arq/src/main/java/org/apache/jena/system/Txn.java
>>
>
>
>
