08.12.2015 16:41, Dimitry Sibiryakov wrote:
> 08.12.2015 15:31, Vlad Khorsun wrote:
>> This code is not the same as code that you blamed and it is not correct
>> at all.
>
> At first, I don't blame your code. It is robust and fast enough. It is
> just a little
Good to know, i had another opinion before ;)
> confusing at first glance and leave some more room for threads racing if you
> take into
> consideration other possible flags.
I see no races there. Especially considering another flags.
> At second, this code is correct because cleanSweepFlags() will clear both
> flags anyway.
No. Code you show is from Database::allowSweepThread() (and i discuss that
code):
while (true)
{
AtomicCounter::counter_type old = dbb_flags;
if ((old & (DBB_sweep_in_progress | DBB_sweep_starting)) ||
(dbb_ast_flags & DBB_shutdown))
return false;
if (dbb_flags.compareExchange(old, old | DBB_sweep_starting))
break;
}
This code must not set DBB_sweep_starting flag if it not going to start
sweep thread.
I.e. if sweep thread:
- already starting
- already started
- not allowed due to database shutdown
With your proposed simplification, code will set DBB_sweep_starting flag in
any case,
even if this thread will not continue. Thus your code is not equal to code
above and
not correct.
Note, cleanSweepFlags() is never called after Database::allowSweepThread().
It is called after
another method - Database::allowSweepRun()
Regards,
Vlad
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