On Sun, 02 Jun 2024 15:14:51 +0200
Bruno Haible wrote:
> Hi Takashi Yano,
>
> > The result is as follows (submitted as v4 patch).
> >
> > int
> > pthread::once (pthread_once_t *once_control, void (*init_routine) (void))
> > {
> > /* Sign bit of once_control->state is used as done flag.
> > Similary, the next significant bit is used as destroyed flag. */
> > const int done = INT_MIN; /* 0b1000000000000000 */
> > const int destroyed = INT_MIN >> 1; /* 0b1100000000000000 */
> > if (once_control->state & done)
> > return 0;
> >
> > /* The type of &once_control->state is int *, which is compatible with
> > LONG * (the type of the pointer argument of InterlockedXxx()). */
> > if ((InterlockedIncrement (&once_control->state) & done) == 0)
> > {
> > pthread_mutex_lock (&once_control->mutex);
> > if (!(once_control->state & done))
> > {
> > init_routine ();
> > InterlockedOr (&once_control->state, done);
> > }
> > pthread_mutex_unlock (&once_control->mutex);
> > }
> > InterlockedDecrement (&once_control->state);
> > if (InterlockedCompareExchange (&once_control->state,
> > destroyed, done) == done)
> > pthread_mutex_destroy (&once_control->mutex);
> > return 0;
> > }
> > ...
> > I believe both codes are equivalent. Could you please check?
>
> Yes, they are equivalent. This code is free of race conditions. (Let's
> hope I am not making a mistake again.)
>
> For legibility I would write the constant values as bit masks:
> 0x80000000
> 0xc0000000
> and - following the habit that constant integers should have names in
> upper case - I would rename
> done → DONE
> destroyed → DESTROYED
Thanks for checking. I'll push the patch after the modification.
--
Takashi Yano <takashi.y...@nifty.ne.jp>
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