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Date: Wed, 17 May 2023 12:37:33 +0200
From: "alice" <alice@...ya.dev>
To: <musl@...ts.openwall.com>
Subject: Re: Question：Why musl call a_barrier in __pthread_once?
On Wed May 17, 2023 at 12:07 PM CEST, =?gb18030?B?ODQ3NTY3MTYx?= wrote:
> Hi,
>
> Why musl add a_barrier() in if branch here?
> 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 == 2) {
> a_barrier();
> return 0;
> }
> return __pthread_once_full(control, init);
> }
>
> https://gitee.com/openharmony/third_party_musl/blob/master/src/thread/pthread_once.c#L44
>
>
> Chuang Yin
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