Why are threads discouraged?

[p5pRT]

Migrated from rt.perl.org#125106 (status was 'open')

Searchable as RT125106$

[p5pRT]

From @ikegami

threads.pm says​:

The use of interpreter-based threads in perl is officially discouraged.

Why is that? Is it just because they're rather heavy? If so, why not just
say so and let the user decide whether he wants to use them or not? After
all, heavy threads aren't a problem if you reuse them (as in a worker
model).

[p5pRT]

From @ribasushi

On 05/05/2015 05​:23 PM, Eric Brine (via RT) wrote​:

# New Ticket Created by "Eric Brine"
# Please include the string​: [perl #125106]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=125106 >

threads.pm says​:

The use of interpreter-based threads in perl is officially discouraged.

Why is that? Is it just because they're rather heavy? If so, why not just
say so and let the user decide whether he wants to use them or not?

+1

[p5pRT]

The RT System itself - Status changed from 'new' to 'open'

[p5pRT]

From @leonerd

On Tue, 5 May 2015 08​:23​:15 -0700
"Eric Brine" (via RT) <perlbug-followup@​perl.org> wrote​:

# New Ticket Created by "Eric Brine"
# Please include the string​: [perl #125106]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=125106 >

threads.pm says​:

The use of interpreter-based threads in perl is officially
discouraged.

Why is that? Is it just because they're rather heavy? If so, why not
just say so and let the user decide whether he wants to use them or
not? After all, heavy threads aren't a problem if you reuse them (as
in a worker model).

Or people could help me finish writing/editing the perlconcurrency doc,
so one day it will explain in more detail​:

  http​://www.leonerd.org.uk/code/perlconcurrency.pod

--
Paul "LeoNerd" Evans

leonerd@​leonerd.org.uk
http​://www.leonerd.org.uk/ | https://metacpan.org/author/PEVANS

[p5pRT]

From @rcaputo

On May 5, 2015, at 11​:23, Eric Brine <perlbug-followup@​perl.org> wrote​:

# New Ticket Created by "Eric Brine"
# Please include the string​: [perl #125106]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=125106 >

threads.pm says​:

The use of interpreter-based threads in perl is officially discouraged.

Why is that? Is it just because they're rather heavy? If so, why not just
say so and let the user decide whether he wants to use them or not? After
all, heavy threads aren't a problem if you reuse them (as in a worker
model).

If your documentation is anything like mine, the paragraph before that statement tries to explain why. Perhaps the discouragement should begin with "Because of this, the use of...." to hint that the reader may have skipped something important and to discourage people from taking a provocative statement out of context.

The discouragement was added on Mar 2, 2014 after an intense deliberation on perl5-porters​:

"RFC​: add discouragement warning to perl threads documentation"
http​://www.gossamer-threads.com/lists/perl/porters/305035

The RFC was a product of an observation in irc.perl.org #p5p that most people in the Perl community, when asked for help with threads in Perl, will harshly denounce their viability and recommend that the problematic program be gutted and rewritten with almost anything but.

The #p5p IRC discussion began on Feb 19, 2014, with "Perl's threads are socially weird. They exist and are supported, but they (and their users) are heavily deprecated in the community."

Or it began with an observation about 90 minutes earlier in a #p5p discussion with/about a Perl novice​:

right, because most channels don't answers threads questions
because most channels are full of people who don't use threads.pm
because 'use threads;' almost always indicates brain damage

--
Rocco Caputo <rcaputo@​pobox.com>

[p5pRT]

From @ikegami

On Tue, May 5, 2015 at 1​:49 PM, Rocco Caputo <rcaputo@​pobox.com> wrote​:

On May 5, 2015, at 11​:23, Eric Brine <perlbug-followup@​perl.org> wrote​:

# New Ticket Created by "Eric Brine"
# Please include the string​: [perl #125106]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=125106 >

threads.pm says​:

The use of interpreter-based threads in perl is officially discouraged.

Why is that? Is it just because they're rather heavy? If so, why not just
say so and let the user decide whether he wants to use them or not? After
all, heavy threads aren't a problem if you reuse them (as in a worker
model).

If your documentation is anything like mine, the paragraph before that
statement tries to explain why. Perhaps the discouragement should begin
with "Because of this, the use of...." to hint that the reader may have
skipped something important and to discourage people from taking a
provocative statement out of context.

One might think that, except that the word "discouraged" is linked to a
definition that means something quite different than "not to be used
without understanding what it means that Perl threads are heavy". It
actually defines "discouraged" as "we'd like to get rid of them, but we're
not doing it now"

  - *discouraged*

  From time to time, we may mark language constructs and features which we
  consider to have been mistakes as *discouraged*. Discouraged features
  aren't currently candidates for removal, but we may later deprecate them if
  they're found to stand in the way of a significant improvement to the Perl
  core.

[p5pRT]

From @xsawyerx

On 05/10/2016 10​:22 PM, Eric Brine wrote​:

On Tue, May 5, 2015 at 1​:49 PM, Rocco Caputo <rcaputo@​pobox.com
<mailto​:rcaputo@​pobox.com>>wrote​:

> On May 5\, 2015\, at 11&#8203;:23\, Eric Brine \<perlbug\-followup@&#8203;perl\.org
\<mailto&#8203;:perlbug\-followup@&#8203;perl\.org>> wrote&#8203;:
>
> \# New Ticket Created by  "Eric Brine"
> \# Please include the string&#8203;:  \[perl \#125106\]
> \# in the subject line of all future correspondence about this issue\.
> \# \<URL&#8203;: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=125106
\<https://rt-archive.perl.org/perl5/Ticket/Display.html?id=125106>>
>
>
> threads\.pm \<http&#8203;://threads\.pm>says&#8203;:
>
> The use of interpreter\-based threads in perl is officially
discouraged\.
>
>
> Why is that? Is it just because they're rather heavy? If so\, why
not just
> say so and let the user decide whether he wants to use them or
not? After
> all\, heavy threads aren't a problem if you reuse them \(as in a
worker
> model\)\.

If your documentation is anything like mine\, the paragraph before
that statement tries to explain why\.  Perhaps the discouragement
should begin with "Because of this\, the use of\.\.\.\." to hint that
the reader may have skipped something important and to discourage
people from taking a provocative statement out of context\.

One might think that, except that the word "discouraged" is linked to
a definition that means something quite different than "not to be used
without understanding what it means that Perl threads are heavy". It
actually defines "discouraged" as "we'd like to get rid of them, but
we're not doing it now"

* *discouraged*

From time to time\, we may mark language constructs and features
which we consider to have been mistakes as \*discouraged\*\.
Discouraged features aren't currently candidates for removal\, but
we may later deprecate them if they're found to stand in the way
of a significant improvement to the Perl core\.

I agree this is a confusing description.

I also like Rocco's comments on describing *why* something is the way it
is, even if briefly. I found an example in the thread Rocco linked[1],
by Aristotle, on how to explain things briefly and clearly​:

"complex data structures are hard to share properly"

The quote is out of context and does not constitute as the patch I would
envision, but it's an example of how to describe something complicated
succinctly. Perhaps we can form a patch describing what we mean by
"discouraged". Having context might excuse us from trying to find a
better term for this than "discouraged".

[1] Thanks, Rocco!

[p5pRT]

From @leonerd

On Wed, 11 May 2016 19​:54​:37 +0200
Sawyer X <xsawyerx@​gmail.com> wrote​:

I agree this is a confusing description.

I also like Rocco's comments on describing *why* something is the way
it is, even if briefly. I found an example in the thread Rocco
linked[1], by Aristotle, on how to explain things briefly and clearly​:

"complex data structures are hard to share properly"

The quote is out of context and does not constitute as the patch I
would envision, but it's an example of how to describe something
complicated succinctly. Perhaps we can form a patch describing what
we mean by "discouraged". Having context might excuse us from trying
to find a better term for this than "discouraged".

[1] Thanks, Rocco!

If we have some better wording I could put it into perlconcurrency.pod
as well...

--
Paul "LeoNerd" Evans

leonerd@​leonerd.org.uk
http​://www.leonerd.org.uk/ | https://metacpan.org/author/PEVANS

[p5pRT]

From choroba@matfyz.cz

The documentation of threads.pm says that perl threads are
"discouraged". This causes lots of confusion, as the term is defined
in perlpolicy in the following way​:

  discouraged
  From time to time, we may mark language constructs and
  features which we consider to have been mistakes as
  discouraged. Discouraged features aren't currently candidates
  for removal, but we may later deprecate them if they're found
  to stand in the way of a significant improvement to the Perl
  core.

See also #125106, which seems to lead nowhere, maybe because it was
too ambitious. This patch provides just the minimal change.

See also http​://www.perlmonks.org/?node_id=1107534 .

Perl Info

Flags:
     category=library
     severity=medium
     module=threads

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[p5pRT]

From choroba@matfyz.cz

0001-Remove-the-word-discouraged-from-threads.patch

From deedc55618b1f84d03e39a88fc89cf4dfb01744d Mon Sep 17 00:00:00 2001
From: "E. Choroba" <choroba@still.ms.mff.cuni.cz>
Date: Sat, 24 Mar 2018 16:46:50 +0100
Subject: [PATCH] Remove the word "discouraged" from threads

Its meaning is defined in perlpolicy and means something else. See
also #125106.
---
 dist/threads/lib/threads.pm | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/dist/threads/lib/threads.pm b/dist/threads/lib/threads.pm
index 1b99567ef2..5e5016e3d7 100644
--- a/dist/threads/lib/threads.pm
+++ b/dist/threads/lib/threads.pm
@@ -143,8 +143,8 @@ system for multitasking that one might expect or hope for.  Threads are
 implemented in a way that make them easy to misuse.  Few people know how to
 use them correctly or will be able to provide help.
 
-The use of interpreter-based threads in perl is officially
-L<discouraged|perlpolicy/discouraged>.
+Therefore, the use of interpreter-based threads in perl is officially
+not recommended.
 
 =head1 SYNOPSIS
 
-- 
2.13.6

[p5pRT]

From @Grinnz

On Sat, Mar 24, 2018 at 12​:31 PM, E. Choroba <perlbug-followup@​perl.org>
wrote​:

# New Ticket Created by "E. Choroba"
# Please include the string​: [perl #133021]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=133021 >

-----------------------------------------------------------------
[Please describe your issue here]

The documentation of threads.pm says that perl threads are
"discouraged". This causes lots of confusion, as the term is defined
in perlpolicy in the following way​:

discouraged
From time to time, we may mark language constructs and
features which we consider to have been mistakes as
discouraged. Discouraged features aren't currently candidates
for removal, but we may later deprecate them if they're found
to stand in the way of a significant improvement to the Perl
core.

See also #125106, which seems to lead nowhere, maybe because it was
too ambitious. This patch provides just the minimal change.

See also http​://www.perlmonks.org/?node_id=1107534 .

'not recommended' seems too lenient. 'strongly recommended against'?

-Dan

[p5pRT]

The RT System itself - Status changed from 'new' to 'open'

[p5pRT]

From @dur-randir

On Sat, 24 Mar 2018 09​:31​:06 -0700, choroba@​matfyz.cz wrote​:

 From time to time\, we may mark language constructs and
 features which we consider to have been mistakes as
 discouraged\. 

Threads in their current implementation are arguable a mistake. You loose ~30% of performance and who-measured-how-much memory by just using perl build with threads. And most of XS CPAN is up to some degree threads-unsafe (pure-perl CPAN is safe, so the goals for threads is reached, but still).

Discouraged features aren't currently candidates
 for removal\, but we may later deprecate them if they're found
 to stand in the way of a significant improvement to the Perl
 core\.

Threads are not going anywhere by this definition. Just discouraged.

[p5pRT]

From @iabyn

On Sun, Mar 25, 2018 at 04​:20​:13PM -0700, Sergey Aleynikov via RT wrote​:

Threads in their current implementation are arguable a mistake. You
loose ~30% of performance and who-measured-how-much memory by just using
perl build with threads.

The test suite on blead on my system runs 17% slower under ithreads, but
that includes running a bunch of ithreads-only tests too. So I think 30%
is overstating it.

I'm not aware that a normal single-threaded process uses significantly
more memory under ithreads.

--
Hofstadter's Law​: It always takes longer than you expect, even when you
take into account Hofstadter's Law.

[p5pRT]

From @wchristian

Since this change doesn't have a ticket attached to it, i figured it would be useful to provide the context of what led to its creation.

This discouragement was introduced by rjbs in commit 10a4597. I've extracted some of the chat log that led to it.

https://gist.github.com/wchristian/97525932a89d0785e07371c60d84209c

And here's the p5p mailing list thread that followed afterwards​:

https://www.nntp.perl.org/group/perl.perl5.porters/2014/03/msg213382.html

It's a lot of material, but i hope it'll help understand the context here.