On Sat, May 17, 2014 at 6:33 AM, Michael Haggerty <mhag...@alum.mit.edu> wrote:
> On 05/16/2014 07:37 PM, Ronnie Sahlberg wrote:
>> Change create_branch to use a ref transaction when creating the new branch.
>> ref_transaction_create will check that the ref does not already exist and 
>> fail
>> otherwise meaning that we no longer need to keep a lock on the ref during the
>> setup_tracking. This simplifies the code since we can now do the transaction
>> in one single step.
>>
>> If the forcing flag is false then use ref_transaction_create since this will
>> fail if the ref already exist. Otherwise use ref_transaction_update.
>
> s/exist/exists/
>
> And the references to ref_transaction_create() in the commit message are
> obsolete.
>

Thanks. Fixed typo and deleted obsolete text.

>>
>> This also fixes a race condition in the old code where two concurrent
>> create_branch could race since the lock_any_ref_for_update/write_ref_sha1
>> did not protect against the ref already existing. I.e. one thread could end 
>> up
>> overwriting a branch even if the forcing flag is false.
>>
>> Reviewed-by: Jonathan Nieder <jrnie...@gmail.com>
>> Signed-off-by: Ronnie Sahlberg <sahlb...@google.com>
>> ---
>>  branch.c | 29 +++++++++++++++--------------
>>  1 file changed, 15 insertions(+), 14 deletions(-)
>>
>> diff --git a/branch.c b/branch.c
>> index 660097b..8bf7588 100644
>> --- a/branch.c
>> +++ b/branch.c
>> @@ -226,7 +226,6 @@ void create_branch(const char *head,
>>                  int force, int reflog, int clobber_head,
>>                  int quiet, enum branch_track track)
>>  {
>> -     struct ref_lock *lock = NULL;
>>       struct commit *commit;
>>       unsigned char sha1[20];
>>       char *real_ref, msg[PATH_MAX + 20];
>> @@ -285,15 +284,6 @@ void create_branch(const char *head,
>>               die(_("Not a valid branch point: '%s'."), start_name);
>>       hashcpy(sha1, commit->object.sha1);
>>
>> -     if (!dont_change_ref) {
>> -             lock = lock_any_ref_for_update(ref.buf, NULL, 0, NULL);
>> -             if (!lock)
>> -                     die_errno(_("Failed to lock ref for update"));
>> -     }
>> -
>> -     if (reflog)
>> -             log_all_ref_updates = 1;
>> -
>>       if (forcing)
>>               snprintf(msg, sizeof msg, "branch: Reset to %s",
>>                        start_name);
>> @@ -301,13 +291,24 @@ void create_branch(const char *head,
>>               snprintf(msg, sizeof msg, "branch: Created from %s",
>>                        start_name);
>>
>> +     if (reflog)
>> +             log_all_ref_updates = 1;
>> +
>> +     if (!dont_change_ref) {
>> +             struct ref_transaction *transaction;
>> +             struct strbuf err = STRBUF_INIT;
>> +
>> +             transaction = ref_transaction_begin();
>> +             if (!transaction ||
>> +                 ref_transaction_update(transaction, ref.buf, sha1,
>> +                                        null_sha1, 0, !forcing, &err) ||
>> +                 ref_transaction_commit(transaction, msg, &err))
>> +                     die("%s", err.buf);
>> +     }
>> +
>>       if (real_ref && track)
>>               setup_tracking(ref.buf + 11, real_ref, track, quiet);
>>
>> -     if (!dont_change_ref)
>> -             if (write_ref_sha1(lock, sha1, msg) < 0)
>> -                     die_errno(_("Failed to write ref"));
>> -
>>       strbuf_release(&ref);
>>       free(real_ref);
>>  }
>>
>
>
> --
> Michael Haggerty
> mhag...@alum.mit.edu
> http://softwareswirl.blogspot.com/
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