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From: iyzsong@member.fsf.org (=?utf-8?B?5a6L5paH5q2m?=)
Subject: Re: [WIP][PATCH] download: Don't report the progress too fast
Date: Thu, 14 Sep 2017 22:20:10 +0800
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In-Reply-To: <877ex6456z.fsf@gnu.org> ("Ludovic
	\=\?utf-8\?Q\?Court\=C3\=A8s\=22'\?\=
	\=\?utf-8\?Q\?s\?\= message of "Sun, 10 Sep 2017 23:25:08 +0200")
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To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Cc: guix-devel@gnu.org

ludo@gnu.org (Ludovic Court=C3=A8s) writes:

> [...]
>> Date: Fri, 8 Sep 2017 22:49:03 +0800
>> Subject: [PATCH] download: Report the progress asynchronously in another
>>  thread.
>>
>> * guix/utils.scm (<progress-reporter>): New record type.
>> (call-with-progress-reporter): New procedure.
>> * guix/build/download.scm (dump-port*, progress-reporter/file): New
>> procedures.
>> (ftp-fetch, http-fetch): Use them.
>> (progress-proc): Remove procedure.
>> * guix/scripts/substitute.scm (progress-report-port): Rewrite in terms of
>> <progress-reporter>.
>> (process-substitution): Adjust accordingly.
>
> Impressive!
>
> I have a couple of concerns though:
>
>   1. Using a thread =E2=80=9Cjust=E2=80=9D for progress reporting seems q=
uite
>      heavyweight, though maybe that=E2=80=99s OK.

Yes..
>
>   2. As per POSIX, we cannot mix =E2=80=98fork=E2=80=99 and threads, so p=
rograms that
>      use =E2=80=98primitive-fork=E2=80=99 should not also use threads.  O=
ne such program
>      is (guix scripts substitute), via =E2=80=98decompressed-port=E2=80=
=99.  Guile
>      rightfully emits a warning when a multithreaded program calls
>      =E2=80=98primitive-fork=E2=80=99:
>
>        https://git.savannah.gnu.org/cgit/guile.git/tree/libguile/posix.c#=
n1224

Oh, thanks for pointing it out!
>
>    3. =E2=80=9CAtomic boxes=E2=80=9D are a Guile 2.2 feature, but we stil=
l support 2.0.
>
> To address these, I would use =E2=80=98abort-to-prompt=E2=80=99 & co., po=
ssibly with
> =E2=80=9Csuspendable ports=E2=80=9D, but this is a 2.2 feature.  (It may =
be that we
> should use Fibers directly.)

Sure, I=E2=80=99d like to try fibers.  When we can drop the support of Guile
2.0?  (I guess one sign is that 2.2 is in the debian stable.)

>
> Tricky!  Not sure what to do here.
>
> Thoughts?

How about replace the use of thread from =E2=80=98progress-reporter/file=E2=
=80=99 by a
=E2=80=98rate-limited=E2=80=99 render procedure, and then change the elapse=
d time to
ETA, which is okay without updating in seconds?