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Date: Thu, 23 Jul 2015 11:58:28 +0200
From: Jens Gustedt <jens.gustedt@...ia.fr>
To: musl@...ts.openwall.com
Subject: implement stdatomic.h library interface
Hello,
about half a year ago well already discussed this, and at that time
Joakim had a proposal for an implementation.
Looking back on this, I think that we had a bit of a wrong focus,
then. The point for musl wouldn't necessarily be to provide the
<stdatomic.h> header itself, but the stub functions that are needed if
the compiler isn't able to inline all operations.
Since I needed it, now, I just went for it and implemented it. For the
moment this isn't integrated to musl but standalone, and for a proper
integration into musl I'd still have some work to do.
At the moment I see three principal possibilities for improvement with
atomics in musl:
(1) Provide the library interfaces that gcc >= 4.8 and clang > 3.6 (?)
need. The interface is well documented, so let's just do it.
(2) Provide an interface to atomics for compilers that don't have it
yet. This can be done more or less easily up to some limits for
all compilers that implement the __sync builtins. gcc 4.8 is a bit
special since it implements the atomic operations but not the type
qualification.
For compilers that don't have __sync or __atomic we could provide
a minimal interface with lock-free _Atomic(int), _Atomic(void*)
and atomic_flag, say.
The limits for these platforms would be that code could only use
the _Atomic(bla) specification for the types and macro calls to
act upon them. But since for pre-C11 compilers this is just an
extension, that would be a start.
(3) Review the internal use of atomics. AFAIR, Rich has already
started to look into that, but in any case that part is probably
independent of the first two points.
In a later stage, once (1) and (2) are stable, we could then look
into using _Atomic(int) and the corresponding macros.
Jens
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