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bh=ECQFOnr+SPNk5oNtdA5LpXi0Ou2QOo0JN7g25E4Pr/4=; b=EoQAyc68P0eume8BTj7dJSrAuHzAUGwW4uBHVNbmRIu8fMXrcogsGN7iEGc49Qz41j WLAKYJjHE4Ffp4y0k4hABmEnErU4U4hW5rNff9j4VnP1D4bu+jSssAYBbn74emW55cPz kG4iLQDDX8CXJlI7LhUglAIwrpQ0aFpKjxgQj5KMN9UPIQiNDAcutzYyJGbEYAq7xhUX lhxdN3/IjAtswyy4n2BvRvZf1tFrPTYl9uuOwkDiAW6yq0H3Wu4lTUfQnqvrNMogFTw8 gBSlu60kPSuMxWRL4eOgYjt9Iv11tiCex5lwOTcRhc+dOMnroVOdVJELDnbKlTuNW+oY QJAg== X-Gm-Message-State: AOAM5320JlNDPttPnmGhfhvXIAkVagJKpYeE9gyxA3IU2DKgnWUDF9ud lEB0ZvbnITVBCohgQT1Jn5IB4k1M1XU= X-Google-Smtp-Source: ABdhPJzIJ7yDH+bIC7xOjTdx5hRkIfCQsHpgV8ZfbS2h+qwvYZ/S6G6Q8a0dtNgTzF0lfK/t2W79uA== X-Received: by 2002:ac8:361b:: with SMTP id m27mr10582626qtb.60.1590066924003; Thu, 21 May 2020 06:15:24 -0700 (PDT) Received: from [192.168.1.4] ([177.194.48.209]) by smtp.googlemail.com with ESMTPSA id n68sm4420653qkb.58.2020.05.21.06.15.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 May 2020 06:15:23 -0700 (PDT) Subject: Re: [PATCH 2/2] manual: Document __libc_single_threaded To: Szabolcs Nagy References: <2c218c9ed9586ed5491f6fa08045d1e883b126c3.1589998207.git.fweimer@redhat.com> <724ecd59-d6e4-9f52-f425-8a4ff795114f@linaro.org> <20200521130927.GF14130@arm.com> Autocrypt: addr=adhemerval.zanella@linaro.org; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200521130927.GF14130@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Adhemerval Zanella via Libc-alpha Reply-To: Adhemerval Zanella Cc: libc-alpha@sourceware.org Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" On 21/05/2020 10:09, Szabolcs Nagy wrote: > The 05/21/2020 09:50, Adhemerval Zanella via Libc-alpha wrote: >> On 20/05/2020 15:12, Florian Weimer via Libc-alpha wrote: >> >>> +@smallexample >>> +if (__libc_single_threaded) >>> + atomic_fetch_add (&reference_count, 1, memory_order_relaxed); >>> +else >>> + atomic_fetch_add (&reference_count, 1, memory_order_acq_rel); >>> +@end smallexample >> >> Shouldn't the access to __libc_single_threaded be atomic itself >> (at least with relaxed semantic)? > > not if we guarantee that this object can only be > written while the process is single threaded. > > (e.g. an exiting detached thread cannot update it > even if only one thread left.. because that may > concurrently read it) > OK, so I think we should outline that atomic operations are not required to acess this object and that once __libc_single_threaded is set 0 it will continue to indicate non-single thread even thread are jointed or detached thread finishes.