so wait, I am confused... is this a deadlock situation?
or is it a JBoss passivation bug?
marc
|-----Original Message-----
|From: [EMAIL PROTECTED]
|[mailto:[EMAIL PROTECTED]]On Behalf Of Nortje, Andrew
|Sent: Wednesday, January 31, 2001 7:23 AM
|To: 'jBoss'
|Subject: RE: [jBoss-User] LOCKING-WAITING (TRANSACTION)
|
|
|Thanks Ole. Always something interesting to learn out there.
|
|> -----Original Message-----
|> From: Ole Husgaard [mailto:[EMAIL PROTECTED]]
|> Sent: Wednesday, January 31, 2001 8:00 AM
|> To: jBoss
|> Subject: Re: [jBoss-User] LOCKING-WAITING (TRANSACTION)
|>
|>
|> Hi,
|>
|> "Nortje, Andrew" wrote:
|> > OK I got it figured. I got the dead lock situation that Ole
|> sketched. BTW if
|> > anyone is dealing with accounts and account balances NEVER
|> update the
|> > account balance when you are inserting line items, you are
|> sure to get
|> > deadlock. Only update the balance once in a while, or when
|> necessary (e.g.
|> > when the customer wants to withdraw funds), from
|> information in the account
|> > line items.
|>
|> One way to get around such deadlocks is by
|> ordering access to you beans within
|> transactions.
|>
|> For example, if you have entity beans Account
|> and AccountLine, with instances account and
|> accountLine, you can get around the deadlock
|> if you always access account first when you need
|> to access both instances.
|>
|> The following two threads might deadlock:
|> 1: accountLine.getAmount(...);
|> account.updateBalance(...);
|> 2: account.getBalance(...);
|> accountLine.getAmount(...);
|>
|> But if Account is always accessed first, no
|> deadlock:
|> 1: account.getBalance(...);
|> accountLine.getAmount(...);
|> account.updateBalance(...);
|> 2: account.getBalance(...);
|> accountLine.getAmount(...);
|>
|> The extra call in thread 1 above ensures that
|> the account is locked first. And if the account
|> is always locked first when you need to lock
|> both account and accountLine, the deadlock
|> scenario I described cannot happen (at least
|> not between these two beans).
|>
|>
|> Best Regards,
|>
|> Ole Husgaard.
|>
|>
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