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From: "Dmitry A. Kazakov" <>
Subject: Re: Broadcast / iterate to all Connection objects via Simple Components?
Date: Mon, 13 Feb 2023 12:57:19 +0100	[thread overview]
Message-ID: <tsd8iu$23ce9$> (raw)
In-Reply-To: <>

On 2023-02-13 12:07, Emmanuel Briot wrote:
> On Monday, February 13, 2023 at 11:55:10 AM UTC+1, Dmitry A. Kazakov wrote:
>> Well, if there is Linux kernel level support why it is not used in
>> socket select as it is in epoll? I would expect them do that at some
>> point or drop epoll... (:-))
> Because in practice the linux developers don't get to modify such APIs, which
> are mandated by Posix, or Unix, or some RFC.
> So the API for select and poll will *never* change.

Well, the API does not really prescribe the actual implementation of 
fd_set. If you need that many elements in the set then using a bitmask 
and not having some bookkeeping to balance load will bit you at some 
point anyway.

> epoll is definitely the modern approach on linux, until of course someone finds
> something even better.  epoll is fully thread safe too, which is very nice when
> used from Ada.
> Using select() is totally outdated at this point, and means you can never handle
> more than 1000 simultaneous clients, and that only if you do not have other
> file descriptors open (database, files,...)

Well, it is indicative how outdated Linux always was. Asynchronous I/O 
was old news long *before* Linus even started his project... (:-))

> The person who developed GNAT.Sockets has left AdaCore a while ago, so "they" (which
> I assume is what your message was referring to) are actually unlikely to update that.

Yes, that is what I expect, a face lifting of Linux implementation of 

> They also have strong concerns about platform-agnostic support, and epoll is linux-specific
> at this point (likely also BSD).

GNAT.Sockets is no thin bindings, I see little problem here. AFAIK BSD 
allows increasing FD_SETSIZE, but I am not sure.

> There exists multiple libraries out there that provide an API
> common to multiple platforms, and that use epoll on linux.  Maybe that's what would make
> sense, but nowadays with Alire, I would expect someone to build a crate there rather than
> AdaCore modify GNAT.Sockets.

That is an option too. However presently I cannot use Alire because last 
time I looked it did not support automated uploading, versioning and 
target dependencies through the GPR.

>> I'd like to have special Ada "tasks" acting as co-routines on top of
>> proper tasks yielding when the socket buffer is empty or full.
> This is an approach we had discussed at AdaCore before I left.  There are multiple drawbacks
> here: the limited stack size for tasks by default (2MB), the fact that entries cannot return indefinite
> types, the fact that currently those tasks are assigned to OS threads (so too many of them does
> impact resource usage),...

My idea is to have these as pseudo-tasks scheduled by the Ada run-time 
and not mapped onto any OS threads. A proper thread would pick up such a 
task and run it until it yields. The crucial point is to use the stack 
of the pseudo-task in place of the thread's stack or backing it up and 
cleaning the portion of the stack at the point of yielding, whatever.

> A colleague had found an external library that would provide several stacks and thus let people
> implement actual co-routines.  We did not do much more work on that, but it was a nice proof
> of concept, and efficient.  I think things are mostly blocked now, as the ARG has been discussing
> these topics for quite a few years now.

I have an impression that ARG's view on co-routines totally ignores the 
use case of communication stacks and other cases state machines show 
their ugly faces...

Dmitry A. Kazakov

  reply	other threads:[~2023-02-13 11:57 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-07 20:29 Broadcast / iterate to all Connection objects via Simple Components? A.J.
2023-02-08  8:55 ` Dmitry A. Kazakov
2023-02-08  9:55 ` Jeffrey R.Carter
2023-02-13  7:28   ` Emmanuel Briot
2023-02-13  8:30     ` Dmitry A. Kazakov
2023-02-13  8:44       ` Emmanuel Briot
2023-02-13 10:55         ` Dmitry A. Kazakov
2023-02-13 11:07           ` Emmanuel Briot
2023-02-13 11:57             ` Dmitry A. Kazakov [this message]
2023-02-13 13:22               ` Niklas Holsti
2023-02-13 15:10                 ` Dmitry A. Kazakov
2023-02-13 16:26                   ` Niklas Holsti
2023-02-13 19:48                     ` Dmitry A. Kazakov
2023-02-15  9:54                       ` Niklas Holsti
2023-02-15 10:57                         ` Dmitry A. Kazakov
2023-02-15 18:37                           ` Niklas Holsti
2023-02-19  1:27                             ` A.J.
2023-02-19  8:29                               ` Dmitry A. Kazakov
2023-02-19 14:37                               ` Niklas Holsti
2023-02-13 15:43                 ` J-P. Rosen
2023-02-13 16:40             ` Jeremy Grosser <>
2023-02-13 20:33 ` Daniel Norte de Moraes
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