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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