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SubjectRe: [v2] Updated locking documentation for transaction_t
Date
Thanks, Ted, for your feedback!
I'll submit a modified version.

- Alex

On 07.04.19 18:52, Theodore Ts'o wrote:
> On Mon, Mar 18, 2019 at 07:42:37PM +0100, Alexander Lochmann wrote:
>> /*t
>> - * Where in the log does this transaction's commit start? [no locking]
>> + * Where in the log does this transaction's commit start?
>> + * [journal_t.j_state_lock]
>> */
>> unsigned long t_log_start;
>
> Well, technically, that's not quite right. It's only assigned in one
> location, and we hold j_state_lock, yes. But that's because we need
> to access journal->j_head. At the point where we set t_log_start, the
> transaction has already been locked down (transaction->t_state >
> T_LOCKED).
>
> Similarly, we happen to be holding j_state where it is currently being
> accessed, but it's not because we needed the lock in order to access
> t_log_start safely.
>
>> /*
>> - * When transaction started
>> + * When transaction started [journal_t.j_state_lock]
>> */
>> unsigned long t_start;
>
> And again, not really. The primary place where t_start is set is when
> the transaction is firstt created, before it's visible anywhere else.
> after that, it is used exclusively by the commit thread, and so no
> locking is necessary. It's true that in the places where it is used,
> j_state_lock happens to be taken, but it's strictly not necessary.
>
>>
>> /*
>> - * When commit was requested
>> + * When commit was requested [journal_t.j_state_lock]
>> */
>> unsigned long t_requested;
>
> Yes, that appears to be correct.
>
>>
>> /*
>> - * Checkpointing stats [j_checkpoint_sem]
>> + * Checkpointing stats [journal_t.j_list_lock]
>> */
>> struct transaction_chp_stats_s t_chp_stats;
>>
>
> This appears to be correct.
>
> - Ted
>

--
Technische Universität Dortmund
Alexander Lochmann PGP key: 0xBC3EF6FD
Otto-Hahn-Str. 16 phone: +49.231.7556141
D-44227 Dortmund fax: +49.231.7556116
http://ess.cs.tu-dortmund.de/Staff/al

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