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Date: Wed, 17 May 2023 12:37:33 +0200
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From: "alice" <alice@ayaya.dev>
To: <musl@lists.openwall.com>
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Subject: =?utf-8?q?Re:_[musl]_Question=EF=BC=9AWhy_musl_call=C2=A0a=5Fbarrier_in_?= =?utf-8?q?=5F=5Fpthread=5Fonce=3F?=

On Wed May 17, 2023 at 12:07 PM CEST, =3D?gb18030?B?ODQ3NTY3MTYx?=3D wrote:
> Hi,
>
> Why musl add&nbsp;a_barrier() in if branch here? =20
> What happend if we remove it? Could you give me more details?

see commit df37d3960abec482e17fad2274a99b790f6cc08b,
removing it would cause issues on weakly-ordered memory models.

>
> int __pthread_once(pthread_once_t *control, void (*init)(void))
> {
> 	/* Return immediately if init finished before, but ensure that
> 	 * effects of the init routine are visible to the caller. */
> 	if (*(volatile int *)control =3D=3D 2) {
> 		a_barrier();
> 		return 0;
> 	}
> 	return __pthread_once_full(control, init);
> }
>
> https://gitee.com/openharmony/third_party_musl/blob/master/src/thread/pth=
read_once.c#L44
>
>
> Chuang Yin