Re: [PATCH v3 17/19] refs.c: change update_ref to use a transaction

From: Ronnie Sahlberg <sahlberg@google.com>
Date: Apr 28, 2014, 18:33 UTC
Message-ID: <CAL=YDWkk9aqDmAA4OAYd-eFNkdKoEdp8gS=n4VyMqAFpknU3Bg@mail.gmail.com>
In-Reply-To: <535AEFAF.9000908@alum.mit.edu>

Thanks.

On Fri, Apr 25, 2014 at 4:28 PM, Michael Haggerty <mhagger@alum.mit.edu> wrote:

Show 27 quoted lines

> On 04/25/2014 06:14 PM, Ronnie Sahlberg wrote:
>> Change the update_ref helper function to use a ref transaction internally.
>>
>> Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
>> ---
>>  refs.c | 23 +++++++++++++++++++----
>>  1 file changed, 19 insertions(+), 4 deletions(-)
>>
>> diff --git a/refs.c b/refs.c
>> index 1557c3c..95df4a9 100644
>> --- a/refs.c
>> +++ b/refs.c
>> @@ -3397,11 +3397,26 @@ int update_ref(const char *action, const char *refname,
>>              const unsigned char *sha1, const unsigned char *oldval,
>>              int flags, enum action_on_err onerr)
>>  {
>> -     struct ref_lock *lock;
>> -     lock = update_ref_lock(refname, oldval, flags, NULL, onerr);
>> -     if (!lock)
>> +     struct ref_transaction *t;
>> +     char *err = NULL;
>> +
>> +     t = ref_transaction_begin();
>> +     if ((!t ||
>> +         ref_transaction_update(t, refname, sha1, oldval, flags,
>> +                                !!oldval)) ||
>> +         (ref_transaction_commit(t, action, &err) && !(t = NULL))) {

This is transient code to just show how ugly this pattern becomes when ref_transaction_commit() implicitly also frees the transaction.

Later patches toward the end of the series will replace this with something nicer. Currently in this patch series I pass a pointer to pointer for the transaction to _commit() but that is perhaps not optimal either. I will try and see how it would look if _commit would not free the transaction at all and the caller would always have to call ref_transaction_free() explicitely.

I am thinking of something like this :

   t = ref_transaction_begin();
   if ((!t ||
       ref_transaction_update(t, ...)) ||
       ref_transaction_commit(t, ...)) {
          ...something...
   }
   ref_transaction_free(t);

Show 13 quoted lines

>
> You seem to have extra parentheses around the first || subexpression.
>
> You also don't need the parentheses around the && expression because &&
> binds more tightly than ||.
>
> But using "!(t = NULL)" in the middle of a conditional expression is
> pretty obscure.  I think you will change this in a later patch, so I
> will defer my comments.
>
>> +          const char *str = "update_ref failed for ref '%s': %s";
>
> Indentation error.

Fixed.

Show 23 quoted lines

>
>> +
>> +             ref_transaction_rollback(t);
>> +             switch (onerr) {
>> +             case UPDATE_REFS_MSG_ON_ERR: error(str, refname, err); break;
>> +             case UPDATE_REFS_DIE_ON_ERR: die(str, refname, err); break;
>> +             case UPDATE_REFS_QUIET_ON_ERR: break;
>> +             free(err);
>> +             }
>>               return 1;
>> -     return update_ref_write(action, refname, sha1, lock, NULL, onerr);
>> +     }
>> +     return 0;
>>  }
>>
>>  static int ref_update_compare(const void *r1, const void *r2)
>>
>
>
> --
> Michael Haggerty
> mhagger@alum.mit.edu
> http://softwareswirl.blogspot.com/