From: Ronnie Sahlberg <sahlberg@google.com>
Date: Thu, 15 May 2014 18:26:10 GMT
Subject: Re: [PATCH v8 02/44] refs.c: allow passing NULL to ref_transaction_free
Message-ID: <CAL=YDW=5BjCkZ9A-En+mG9CcshC0tCP4j4ZWKSWK5NEfykWy8Q@mail.gmail.com>
In-Reply-To: <20140515181512.GC26471@google.com>

Thanks.

I used your improved text in the commit message.

On Thu, May 15, 2014 at 11:15 AM, Jonathan Nieder <jrnieder@gmail.com> wrote:
> Ronnie Sahlberg wrote:
>
>> Allow ref_transaction_free to be called with NULL and as a result allow
>> ref_transaction_rollback to be called for a NULL transaction.
>>
>> This allows us to write code that will
>>   if ( (!transaction ||
>>         ref_transaction_update(...))  ||
>>       (ref_transaction_commit(...) && !(transaction = NULL)) {
>>           ref_transaction_rollback(transaction);
>>           ...
>>   }
>>
>> In this case transaction is reset to NULL IFF ref_transaction_commit() was
>> invoked and thus the rollback becomes ref_transaction_rollback(NULL) which
>> is safe. IF the conditional triggered prior to ref_transaction_commit()
>> then transaction is untouched and then ref_transaction_rollback(transaction)
>> will rollback the failed transaction.
>
> I still think these last two paragraphs confuse more than enlighten
> here.  There's plenty of time to explain them in the patch that uses
> that code.
>
> I'd just say something like
>
>         Allow ref_transaction_free(NULL) and hence ref_transaction_rollback(NULL)
>         as no-ops.
>
>         This makes ref_transaction_rollback easier to use and more similar to
>         plain 'free'.
>
> And maybe:
>
>         In particular, it lets us rollback unconditionally as part of cleanup
>         code after setting 'transaction = NULL' if a transaction has been
>         committed or rolled back already.
>
> Thanks,
> Jonathan