标签
PostgreSQL , 10.0 , atomic , spinlock
背景
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.de
10.0 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。
参考
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=b64d92f1a
