From: Iain Sandoe <iain@sandoe.co.uk>
To: "Nicolas König" <koenigni@student.ethz.ch>,
"Thomas Koenig" <tkoenig@netcologne.de>
Cc: Fortran List <fortran@gcc.gnu.org>, dhumieres.dominique@free.fr
Subject: Re: Update on shared memory coarrays
Date: Sun, 3 Jan 2021 10:46:11 +0000 [thread overview]
Message-ID: <5683F724-2723-4EE4-AC50-83FDB598D238@sandoe.co.uk> (raw)
In-Reply-To: <191C9834-F907-4CF0-B652-16E04A42B7AB@sandoe.co.uk>
Iain Sandoe <iain@sandoe.co.uk> wrote:
> Iain Sandoe <iain@sandoe.co.uk> wrote:
>
>> Nicolas König <koenigni@student.ethz.ch> wrote:
>> [IIUC what you mean by double-mapping] Allocating the same thing twice
>> seems likely to be an accident waiting to happen :) ..
>
> So the intent is:
>
> shm_allocate
>
> size the shm
>
> mmap the shm
>
> resize the shm
Actually, it’s not the second mapping that’s failing - it’s the attempt to
resize the shm by using ftruncate() a second time with a larger value.
A quick test says Linux seems to accept the resize, Darwin doesn’t (maybe
this is a Darwin bug - not sure if the ability to resize via this mechanism
is a Posix SUSv3 requirement - need to read the Posix info).
[aside: I tried various other permutations, such as duping the fd and then
attempting to modify the dup, also using fcntl with F_PREALLOCATE]
Anyway, the attempt to resize appears to render the fd invalid, and then
any subsequent use of it fails (which is what the second mmap is reporting).
Without doing the resize, a second mmap succeeds (AFAICT).
> will poke some more if I have a chance.
There is an alternate shm interface on Darwin that allows manipulation of
the shm object more directly (and mapping/unmapping etc).
It’s not clear if that mechanism will allow the shm object to be resized,
it doesn’t say in the man page that one cannot - but it doesn’t say one can
either.
If I have a chance, I’ll try to recode the testcase to use that interface
and see if it works.
OTOH, perhaps you already have an idea about how to side-step the issue -
as noted before it seems possible that the resize would involve a
reallocation (I note that the sucessful second mmap on Linux does have a
different starting address - but that doesn’t prove it was copied, of
course).
Iain
next prev parent reply other threads:[~2021-01-03 10:46 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-29 19:09 dhumieres.dominique
2020-11-30 6:21 ` Thomas Koenig
2020-11-30 15:41 ` dhumieres.dominique
2020-11-30 22:13 ` Thomas Koenig
2020-12-02 17:41 ` dhumieres.dominique
2020-12-03 7:27 ` Thomas Koenig
2020-12-21 12:24 ` dhumieres.dominique
2020-12-21 13:04 ` Thomas Koenig
2020-12-22 12:28 ` dhumieres.dominique
2020-12-22 15:10 ` Thomas Koenig
2020-12-22 16:12 ` Paul Richard Thomas
2020-12-23 9:09 ` Thomas Koenig
2020-12-23 9:38 ` Paul Richard Thomas
2020-12-23 10:47 ` Thomas Koenig
2020-12-26 12:10 ` Paul Richard Thomas
2020-12-26 13:01 ` Thomas Koenig
2020-12-27 15:38 ` Thomas Koenig
2020-12-23 16:42 ` Nicolas König
2020-12-23 17:25 ` dhumieres.dominique
2020-12-27 17:10 ` Nicolas König
2021-01-01 13:51 ` dhumieres.dominique
2021-01-01 16:16 ` Thomas Koenig
2021-01-01 16:41 ` dhumieres.dominique
2021-01-02 20:45 ` Thomas Koenig
2021-01-02 20:55 ` Iain Sandoe
2021-01-02 21:43 ` Thomas Koenig
2021-01-02 22:37 ` Nicolas König
2021-01-02 21:44 ` Iain Sandoe
2021-01-02 22:09 ` Iain Sandoe
2021-01-03 10:46 ` Iain Sandoe [this message]
2021-01-03 14:54 ` Iain Sandoe
2021-01-03 15:42 ` Iain Sandoe
2021-01-03 21:53 ` Thomas Koenig
2021-01-04 2:34 ` Iain Sandoe
2021-01-04 18:54 ` Nicolas König
2021-01-05 13:11 ` Iain Sandoe
2021-01-05 13:23 ` Iain Sandoe
2021-01-05 13:27 ` Thomas Koenig
2021-01-05 13:34 ` Iain Sandoe
2021-01-05 14:54 ` Nicolas König
2021-01-05 14:28 ` Iain Sandoe
2021-01-05 15:45 ` Nicolas König
[not found] ` <BAD6EA1D-BB9F-4905-ADD1-76FA1D6B9591@sandoe.co.uk>
2021-01-05 17:11 ` Nicolas König
2021-01-06 16:56 ` Iain Sandoe
-- strict thread matches above, loose matches on Subject: below --
2020-11-29 13:10 Nicolas König
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