[storm] Consistent multithreaded operations

[Jamu Kakar]

Hi,

NeedBenzyn NeedBenzyn wrote:
> I'd like to know what would be the proper way in storm to execute that 
> kind of code on a multithreaded server (acessing MySql server InnoDb 
> tables):
> 
>     def bankOperation():
> 
>         account = store.find(BankAccount,BankAccount.id == 1).one()
>         if account == None:
>             return
> 
>         #Simulate some processing
>         waittime = random.random()*4
>         time.sleep(waittime)
> 
>         account.value = account.value + 100
> 
>         store.flush()        
>         store.commit()
> 
> ==> If I have more than one thread executing that code data become 
> inconsistent.

You need to make sure you use one Store per-thread.  Something like
this (untested) code should work:

def bank_operation(store, id):
     account = store.find(BankAccount, BankAccount.id == id).one()
     if account:
         account.value += 100


def run_thread():
     store = Store(create_database(...))
     try:
         bank_operation(store, 1)
     except:
         store.rollback()
         raise
     else:
         store.commit()

Storm automatically uses transactions, so you shouldn't have to
worry about locking tables and such (though this may not be true for
SQLite).

Thanks,
J.