PostgreSQL , 10.0 , atomic , spinlock
起源
Add a basic atomic ops API abstracting away platform/architecture details. author Andres Freund <andres@anarazel.de> Fri, 26 Sep 2014 05:49:05 +0800 (23:49 +0200) committer Andres Freund <andres@anarazel.de> Fri, 26 Sep 2014 05:49:05 +0800 (23:49 +0200) commit b64d92f1a5602c55ee8b27a7ac474f03b7aee340 tree 2ac33fb70d31585297ae8baeb674ef757544a1d7 tree | snapshot parent 9111d46351e8c3d82452a7454e43ccbf1991b3dc commit | diff Add a basic atomic ops API abstracting away platform/architecture details. Several upcoming performance/scalability improvements require atomic operations. This new API avoids the need to splatter compiler and architecture dependent code over all the locations employing atomic ops. For several of the potential usages it'd be problematic to maintain both, a atomics using implementation and one using spinlocks or similar. In all likelihood one of the implementations would not get tested regularly under concurrency. To avoid that scenario the new API provides a automatic fallback of atomic operations to spinlocks. All properties of atomic operations are maintained. This fallback - obviously - isn't as fast as just using atomic ops, but it's not bad either. For one of the future users the atomics ontop spinlocks implementation was actually slightly faster than the old purely spinlock using implementation. That's important because it reduces the fear of regressing older platforms when improving the scalability for new ones. The API, loosely modeled after the C11 atomics support, currently provides 'atomic flags' and 32 bit unsigned integers. If the platform efficiently supports atomic 64 bit unsigned integers those are also provided. To implement atomics support for a platform/architecture/compiler for a type of atomics 32bit compare and exchange needs to be implemented. If available and more efficient native support for flags, 32 bit atomic addition, and corresponding 64 bit operations may also be provided. Additional useful atomic operations are implemented generically ontop of these. The implementation for various versions of gcc, msvc and sun studio have been tested. Additional existing stub implementations for * Intel icc * HUPX acc * IBM xlc are included but have never been tested. These will likely require fixes based on buildfarm and user feedback. As atomic operations also require barriers for some operations the existing barrier support has been moved into the atomics code. Author: Andres Freund with contributions from Oskari Saarenmaa Reviewed-By: Amit Kapila, Robert Haas, Heikki Linnakangas and Álvaro Herrera Discussion: CA+TgmoYBW+ux5-8Ja=Mcyuy8=VXAnVRHp3Kess6Pn3DMXAPAEA@mail.gmail.com, 20131015123303.GH5300@awork2.anarazel.de, 20131028205522.GI20248@awork2.anarazel.de10.0 新增64bit atomic支持
Improve 64bit atomics support. author Andres Freund <andres@anarazel.de> Sat, 8 Apr 2017 05:44:47 +0800 (14:44 -0700) committer Andres Freund <andres@anarazel.de> Sat, 8 Apr 2017 05:48:11 +0800 (14:48 -0700) commit e8fdbd58fe564a29977f4331cd26f9697d76fc40 tree 7ac78010b4ad51730fe948a79e7c5d7e5f461981 tree | snapshot parent 28afad5c85b436f19d9f2c0e3197c7db960fef6f commit | diff Improve 64bit atomics support. When adding atomics back in b64d92f1a, I added 64bit support as optional; there wasn't yet a direct user in sight. That turned out to be a bit short-sighted, it'd already have been useful a number of times. Add a fallback implementation of 64bit atomics, just like the one we have for 32bit atomics. Additionally optimize reads/writes to 64bit on a number of platforms where aligned writes of that size are atomic. This can now be tested with PG_HAVE_8BYTE_SINGLE_COPY_ATOMICITY. Author: Andres Freund Reviewed-By: Amit Kapila Discussion: https://postgr.es/m/20160330230914.GH13305@awork2.anarazel.de这个patch的讨论，详见邮件组，本文末尾URL。
PostgreSQL社区的作风非常严谨，一个patch可能在邮件组中讨论几个月甚至几年，根据大家的意见反复的修正，patch合并到master已经非常成熟，所以PostgreSQL的稳定性也是远近闻名的。
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=e8fdbd58fe564a29977f4331cd26f9697d76fc40
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=b64d92f1a
