From: Pedro Giffuni <pfg@FreeBSD.org>
To: Felix Fietkau <nbd@openwrt.org>, musl@lists.openwall.com
Subject: Re: FreeBSD's Google Summer of Code 2016
Date: Mon, 7 Mar 2016 08:10:21 -0500 [thread overview]
Message-ID: <56DD7DBD.6010703@FreeBSD.org> (raw)
In-Reply-To: <56DD3C91.2070403@openwrt.org>
On 03/07/16 03:32, Felix Fietkau wrote:
> On 2016-03-06 01:25, Rich Felker wrote:
>> On Sat, Mar 05, 2016 at 07:14:34PM -0500, Pedro Giffuni wrote:
... <snip>
>>> Of course I ahould have meant "based on regular FreeBSD kernel services".
>>>
>>>>> http://thread.gmane.org/gmane.linux.debian.ports.bsd/11702
>>>>>
>>>>> I am certain this will require more research but it would be useful
>>>>> for other ports as well.
>>>>
>>>
>>> We could ask Petr Salinger for the details, but I am pretty sure
>>> FreeBSD has the required functionality natively.
>>>
>>>> Glibc/NPTL has a lot of what I'd call "gratuitous abstraction" (like
>>>> the lll stuff) in their pthread primitives which makes this
>>>> "possible". I call it gratuitous because it's really really hard to
>>>> achieve correct implementations of the pthread sync primitives that
>>>> don't have serious corner-case bugs, and it's unlikely that their
>>>> abstractions actually suffice to make correct alternate
>>>> implementations.
>>>>
>>>> musl does not have any such abstraction. We require a compare-and-swap
>>>> operation or equivalent on which arbitrary atomic operations can be
>>>> constructed, a futex or equivalent operation that's roughly
>>>> while(*addr==expected) sleep(), and implement all the sync primitives
>>>> just once on top of these.
>>>>
>>>
>>> I am not a threading expert (or even a CS guy), but it sounds like
>>> mutex(9) with condvar(9) would do [1]:
>>
>> No, they don't satisfy the needs of musl; they have their own
>> additional storage requirements and are probably not AS-safe. It might
>> be possible to use them to implement a userspace-emulated futex queue
>> (only if they are AS-safe), but I don't see a way to extend that to
>> the process-shared case.
> What about umtx? It's supposed to be just like linux futex.
>
Yes, that's it.
It is not well documented beyond the <sys/umtx.h> header but it
is indeed used to implement the linux abi futex and the native
libthr on FreeBSD.
Pedro.
prev parent reply other threads:[~2016-03-07 13:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-05 20:11 Pedro Giffuni
2016-03-05 21:25 ` Rich Felker
2016-03-05 22:41 ` Pedro Giffuni
2016-03-05 23:32 ` Rich Felker
2016-03-06 0:14 ` Pedro Giffuni
2016-03-06 0:25 ` Rich Felker
2016-03-06 0:31 ` Rich Felker
2016-03-06 1:11 ` Pedro Giffuni
2016-03-06 0:59 ` Pedro Giffuni
2016-03-06 1:08 ` Rich Felker
2016-03-07 8:32 ` Felix Fietkau
2016-03-07 13:06 ` Szabolcs Nagy
2016-03-07 14:22 ` Pedro Giffuni
2016-03-07 13:10 ` Pedro Giffuni [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=56DD7DBD.6010703@FreeBSD.org \
--to=pfg@freebsd.org \
--cc=musl@lists.openwall.com \
--cc=nbd@openwrt.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).