From: Michael Haggerty <mhagger@alum.mit.edu>
To: Junio C Hamano <gitster@pobox.com>
Cc: "Stefan Beller" <sbeller@google.com>,
"Ronnie Sahlberg" <ronniesahlberg@gmail.com>,
"Jonathan Nieder" <jrnieder@gmail.com>,
"Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>,
"Git Mailing List" <git@vger.kernel.org>
Subject: Re: [PATCH v2 04/12] ref_transaction_update(): remove "have_old" parameter
Date: Fri, 13 Feb 2015 18:15:33 +0100 [thread overview]
Message-ID: <54DE3135.7070902@alum.mit.edu> (raw)
In-Reply-To: <CAPc5daX80Mk2cRNAijTckHZ-EFJhiF4GHWMxBK4wYJYSwaEe0w@mail.gmail.com>
On 02/12/2015 06:32 PM, Junio C Hamano wrote:
> On Thu, Feb 12, 2015 at 3:12 AM, Michael Haggerty <mhagger@alum.mit.edu> wrote:
>> Instead, verify the reference's old value if and only if old_sha1 is
>> non-NULL.
>>
>> ...
>> @@ -3664,9 +3664,6 @@ int ref_transaction_update(struct ref_transaction *transaction,
>> if (transaction->state != REF_TRANSACTION_OPEN)
>> die("BUG: update called for transaction that is not open");
>>
>> - if (have_old && !old_sha1)
>> - die("BUG: have_old is true but old_sha1 is NULL");
>> -
>
> In the old world, old_sha1 here used to be one of
> (1) NULL, (2) null_sha1[], or (3) a real object name.
> What is the rule in the new world?
The new world is explained in the docstring in refs.h, which was updated
in this same commit:
If old_sha1 is non-NULL, then it the value
that the reference should have had before the update, or null_sha1
if it must not have existed beforehand.
The docstring is further revised later in the patch series to
old_sha1 is the value that the reference must have
before the update, or null_sha1 if it must not have existed
beforehand. The old value is checked after the lock is taken to
prevent races. If the old value doesn't agree with old_sha1, the
whole transaction fails. If old_sha1 is NULL, then the previous
value is not checked.
The new rule is extended to ref_transaction_delete() in the subsequent
commit. I like the new semantics because it removes redundancy in the
interpretation of parameters.
Is that explanation adequate?
Michael
--
Michael Haggerty
mhagger@alum.mit.edu
next prev parent reply other threads:[~2015-02-13 17:15 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-12 11:12 [PATCH v2 00/12] Allow reference values to be checked in a transaction Michael Haggerty
2015-02-12 11:12 ` [PATCH v2 01/12] refs: move REF_DELETING to refs.c Michael Haggerty
2015-02-12 11:12 ` [PATCH v2 02/12] refs: remove the gap in the REF_* constant values Michael Haggerty
2015-02-12 11:12 ` [PATCH v2 03/12] struct ref_update: move "have_old" into "flags" Michael Haggerty
2015-02-12 18:08 ` Stefan Beller
2015-02-12 19:15 ` Junio C Hamano
2015-02-17 14:37 ` Michael Haggerty
2015-02-17 15:52 ` Junio C Hamano
2015-02-12 11:12 ` [PATCH v2 04/12] ref_transaction_update(): remove "have_old" parameter Michael Haggerty
2015-02-12 17:32 ` Junio C Hamano
2015-02-13 17:15 ` Michael Haggerty [this message]
2015-02-13 18:27 ` Junio C Hamano
2015-02-12 11:12 ` [PATCH v2 05/12] ref_transaction_delete(): " Michael Haggerty
2015-02-12 11:12 ` [PATCH v2 06/12] commit: add tests of commit races Michael Haggerty
2015-02-12 18:13 ` Stefan Beller
2015-02-17 14:44 ` Michael Haggerty
2015-02-12 19:36 ` Junio C Hamano
2015-02-17 15:06 ` Michael Haggerty
2015-02-12 11:12 ` [PATCH v2 07/12] commit: avoid race when creating orphan commits Michael Haggerty
2015-02-12 19:36 ` Junio C Hamano
2015-02-12 11:12 ` [PATCH v2 08/12] ref_transaction_create(): check that new_sha1 is valid Michael Haggerty
2015-02-12 11:12 ` [PATCH v2 09/12] ref_transaction_delete(): check that old_sha1 is not null_sha1 Michael Haggerty
2015-02-12 11:12 ` [PATCH v2 10/12] ref_transaction_verify(): new function to check a reference's value Michael Haggerty
2015-02-12 18:21 ` Stefan Beller
2015-02-12 11:12 ` [PATCH v2 11/12] update_ref(): improve documentation Michael Haggerty
2015-02-12 11:12 ` [PATCH v2 12/12] refs.h: Remove duplication in function docstrings Michael Haggerty
2015-02-12 19:44 ` [PATCH v2 00/12] Allow reference values to be checked in a transaction Junio C Hamano
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