On Feb 12, 9:16 am, Baz <[EMAIL PROTECTED]> wrote:
> May not be your best bet, but can't you start a transaction and retry until
> complete?
Well a transaction is good and useful, but it only contains writes, so
it still allows Thread B to come along and read the old position
values the instant before Thread A makes its UPDATEs. Then as Thread B
finishes its UPDATEs based on the now out-of-date values, it screws
things up.
Of course this is super rare and may take millions of tries. My
current app has 5 list items and one administrator, so not much of a
worry. But if you have a lot of concurrent users then it could
eventually happen.
> On Feb 12, 2008 7:49 AM, sbeam <[EMAIL PROTECTED]> wrote:
>
>
>
> > On Feb 12, 5:59 am, wirtsi <[EMAIL PROTECTED]> wrote:
> > > so I'll just go over to this thread with my problems :)
>
> > sorry for derailing your thread ;)
>
> > > ...
> > > function beforeSave()
> > > {
> > > $this->query("LOCK TABLE {$this->table} AS Framejob WRITE,
> > > {$this->table} WRITE,
> > > queues AS Queue WRITE,jobcolumns as Jobcolumn
> > > WRITE,storages as Storage WRITE,
> > > lenscolors as Lenscolor WRITE,framecolors as
> > > Framecolor WRITE,names as Name WRITE");
>
> > > }
>
> > > Any idea what to do?
>
> > I think you are describing a classic race condition.
> >http://en.wikipedia.org/wiki/Race_condition
>
> > A problem for sure, the list ordering may run perfectly for years and
> > then blow up one day while you are on vacation.
>
> > I don't think you will be able to fix it with LOCK TABLES in mySQL.
> > Hopefully you are using InnoDB anyway and it becomes irrelevant. LOCK
> > TABLES can't prevent Thread B from reading the table, which is what
> > you need to do.
>
> > In mySQL maybe you can try GET_LOCK()
>
> >http://dev.mysql.com/doc/refman/5.0/en/miscellaneous-functions.html#f...
>
> > So run "SELECT GET_LOCK('L1',10)" before you proceed. If Thread B
> > comes along and needs to wait until Thread A is finished doing it's
> > business, then it will (i think ---haven't tested)
>
> > how then to make it DB-agnostic is another issue. Anyone?
>
> > have fun
> > Sam
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