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digitalmars.D.announce - Interview with InformIT part 2/3

reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
http://www.informit.com/articles/article.aspx?p=1622265

Andrei
Aug 18 2010
next sibling parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
On 08/18/2010 05:13 AM, Andrei Alexandrescu wrote:
 http://www.informit.com/articles/article.aspx?p=1622265

 Andrei

Now on reddit: http://www.reddit.com/r/programming/comments/d2j8n/d_programming_language_interview_with_andrei/ Thanks davebrk! Andrei
Aug 18 2010
next sibling parent reply bearophile <bearophileHUGS lycos.com> writes:
Andrei Alexandrescu:
 http://www.reddit.com/r/programming/comments/d2j8n/d_programming_language_interview_with_andrei/

I will need time to digest this interesting second part of your interview, you say many complex things. In the meantime that Reddit thread is one of the worst I've seen on that usually interesting site. Some C++ programmers seem to hate D a lot. Each new programming language is built on different values. Maybe D2 is not targeted to most of the experienced C++ programmers. Maybe D2 is more fit for other kinds of programmers, after all. I don't know. Among all the comments written by axilmar, I agree that D tuples are not in good shape at all. There are two of them, one is limited (no way to return them) and auto-flattening, the other has no compiler support despite some syntax sugar helps a lot here. Regarding this you have written in Reddit:
Even moving classes should be fine with precautions, as moving garbage
collectors have shown.<

Currently in the D2 GC there is no notion of pinned/unpinned class instances, but eventually an attribute as pinned may be added to D3, plus its related semantics. It adds complexity to the language and it needs to interact with the GC, so it will get useful as the D GC becomes more modern (with different zones for newly allocated objects, etc). Bye, bearophile
Aug 18 2010
next sibling parent reply Walter Bright <newshound2 digitalmars.com> writes:
bearophile wrote:
 Currently in the D2 GC there is no notion of pinned/unpinned class instances,
 but eventually an attribute as  pinned may be added to D3, plus its related
 semantics. It adds complexity to the language and it needs to interact with
 the GC, so it will get useful as the D GC becomes more modern (with different
 zones for newly allocated objects, etc).

There is no need for a pin attribute, the gc can determine if a class needs pinning or not.
Aug 18 2010
next sibling parent reply Walter Bright <newshound2 digitalmars.com> writes:
Leandro Lucarella wrote:
 Walter Bright, el 18 de agosto a las 10:08 me escribiste:
 bearophile wrote:
 Currently in the D2 GC there is no notion of pinned/unpinned class instances,
 but eventually an attribute as  pinned may be added to D3, plus its related
 semantics. It adds complexity to the language and it needs to interact with
 the GC, so it will get useful as the D GC becomes more modern (with different
 zones for newly allocated objects, etc).

class needs pinning or not.

As long as the precise heap scanning patch is applied (and much better if we can manage to scan the static data precisely too). Otherwise you simply just can't move stuff around because you don't know what is a pointer and what is not (thus you can't update pointer that point to moved stuff).

Hence the objects with ambiguous references to them get automatically pinned by the gc. I've implemented such a gc before, it works fine. It's called a "mostly copying collector". Besides, any scheme where you have to manually mark pinnable objects is doomed to have disastrously subtle and hard-to-find bugs.
Aug 18 2010
parent Walter Bright <newshound2 digitalmars.com> writes:
Leandro Lucarella wrote:
 With the precise heap scanning patch for DMD the GC can automatically
 pin memory, because it has enough information to differentiate between
 real pointers and words which types are not really known, so a block can
 be moved *only* if is only pointed to by real pointers, otherwise is
 pinned because we can't update the words with unknown type if we moved
 that block.

I know. That's how a mostly copying collector works.
Aug 19 2010
prev sibling parent reply bearophile <bearophileHUGS lycos.com> writes:
Walter Bright:

 There is no need for a pin attribute, the gc can determine if a class needs 
 pinning or not.

The same is probably true for pure functions too, the compiler can determine what functions are pure and what are not pure. But the purpose of a pinned is that: 1) The default becomes unpinned. This is good for the GC, because moving memory around is good to compact the heap, etc. 2) The programmer states hir/her/his purpose, this is documentation, but it's an alive documentation because as with pure the compiler is able to determine if the attribute is used wrongly, and give a compile time error in such case. Bye, bearophile
Aug 18 2010
parent Walter Bright <newshound2 digitalmars.com> writes:
bearophile wrote:
 Walter Bright:
 
 There is no need for a pin attribute, the gc can determine if a class needs
  pinning or not.

The same is probably true for pure functions too, the compiler can determine what functions are pure and what are not pure. But the purpose of a pinned is that: 1) The default becomes unpinned. This is good for the GC, because moving memory around is good to compact the heap, etc. 2) The programmer states hir/her/his purpose, this is documentation, but it's an alive documentation because as with pure the compiler is able to determine if the attribute is used wrongly, and give a compile time error in such case.

The other problem with a pinned/notpinned object is the object itself cannot control who or how someone is pointing to it.
Aug 18 2010
prev sibling next sibling parent Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
On 08/18/2010 11:59 AM, bearophile wrote:
 Andrei Alexandrescu:
 http://www.reddit.com/r/programming/comments/d2j8n/d_programming_language_interview_with_andrei/


interview, you say many complex things. In the meantime that Reddit thread is one of the worst I've seen on that usually interesting site. Some C++ programmers seem to hate D a lot. Each new programming language is built on different values. Maybe D2 is not targeted to most of the experienced C++ programmers. Maybe D2 is more fit for other kinds of programmers, after all. I don't know.

I'm not seeing much hatred in that thread, and in fact overall the reception of D on reddit has improved enormously since e.g. six months ago. There are of course those exhausting bullet points, which look like reverse engineering of an argument starting from conclusion. That's fine, and it seems like not many fell for it. Andrei
Aug 18 2010
prev sibling next sibling parent "Nick Sabalausky" <a a.a> writes:
"bearophile" <bearophileHUGS lycos.com> wrote in message 
news:i4h3hf$31eh$1 digitalmars.com...
 In the meantime that Reddit thread is one of the worst I've seen on that 
 usually interesting site.

That seemed to mainly just be that one guy (the one that kept making a bunch of absurd and self-contradictory statements).
Aug 18 2010
prev sibling parent ponce <contact g1a2m3es4f5r6om7m8ars.fr> writes:
 In the meantime that Reddit thread is one of the worst I've seen on that
usually interesting site. Some C++ programmers seem to hate D a lot.

In my experience, convincing someone who have personally invested a lot in C++ is _hard_. People who care about big teams are not convinced at all by language features, and need to be told more about the safety concerns, gettting less bugs, improved productivity.
Aug 19 2010
prev sibling parent Jonathan M Davis <jmdavisprog gmail.com> writes:
On Wednesday, August 18, 2010 09:59:27 bearophile wrote:
 Andrei Alexandrescu:
 http://www.reddit.com/r/programming/comments/d2j8n/d_programming_language
 _interview_with_andrei/

I will need time to digest this interesting second part of your interview, you say many complex things. In the meantime that Reddit thread is one of the worst I've seen on that usually interesting site. Some C++ programmers seem to hate D a lot. Each new programming language is built on different values. Maybe D2 is not targeted to most of the experienced C++ programmers. Maybe D2 is more fit for other kinds of programmers, after all. I don't know.

Every language has those who like it and those who don't. And everyone who uses a language has their own reasons for liking it or disliking. In many ways, D is striking the spot between C++ and Java/C#. It's trying to have the power and efficiency of C++ while having the saftey of Java and C#. As such, it will attract people from both camps, but there are going to be people from both camps who aren't going to like it, if nothing else because it goes too far towards the other end of the spectrum for them. And when you like one language and are well aware of its pros and cons and then go and look at another language, it's very easy to see things that don't match what you like about the language that you know, and without really working with it, you're not really going to be well enough of all of its pros and cons to really decide whether those differences are worth it. I'm both a C++ and Java programmer, and I love D. In many ways, it's exactly what I'm looking for in a language, which is why I'm so excited about it, but there are plenty of things in D which can be very annoying - like the lack of struct default constructors (or as you mentioned, the state of tuples). Ultimately, the folks who are most likely to be interested in D are those who aren't entirely happy with the language that they're using and find D's feature set to be an attractive alternative - that and the folks who are forced to use it because that's what's being used on the project that they're working on, but that's likely fairly rare at this point. In any case, I'm certain that there are a lot of C++ programmers who will love D and a lot who will hate it. - Jonathan M Davis
Aug 18 2010
prev sibling next sibling parent reply "Vladimir Panteleev" <vladimir thecybershadow.net> writes:
On Wed, 18 Aug 2010 13:13:25 +0300, Andrei Alexandrescu  
<SeeWebsiteForEmail erdani.org> wrote:

 http://www.informit.com/articles/article.aspx?p=1622265

Thanks, that was an interesting read. It's possible that I'm missing something, but I think that C++'s default constructors + reference-type structs/classes allow a pattern which isn't easily translatable to D. For example, in C++... class A { /* a class with a default constructor */ }; struct B { A a; /* ... */ }; struct C { B b; /* ... */ }; Now, instantiating C will invoke A's constructors. In order for this to work, the compiler automatically generates hidden constructors for B and C. However, D doesn't have default constructors for structs (and, according to TDPL, never will)? D does seem to generate hidden postblit constructors and destructors, though. If I had to port a C++ project to D which made heavy use of this pattern, what would be the best way to do it? The only ways I see is either rewriting the code to use classes (which means writing constructors with explicit instantiation, more dereferences and heap usage leading to worse performance...), or implementing and calling pseudo-constructors in both B and C, and (most importantly) all places which "instantiate" C. Did I miss anything? -- Best regards, Vladimir mailto:vladimir thecybershadow.net
Aug 18 2010
parent Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
On 08/18/2010 06:46 AM, Vladimir Panteleev wrote:
 On Wed, 18 Aug 2010 13:13:25 +0300, Andrei Alexandrescu
 <SeeWebsiteForEmail erdani.org> wrote:

 http://www.informit.com/articles/article.aspx?p=1622265

Thanks, that was an interesting read. It's possible that I'm missing something, but I think that C++'s default constructors + reference-type structs/classes allow a pattern which isn't easily translatable to D. For example, in C++... class A { /* a class with a default constructor */ }; struct B { A a; /* ... */ }; struct C { B b; /* ... */ }; Now, instantiating C will invoke A's constructors. In order for this to work, the compiler automatically generates hidden constructors for B and C. However, D doesn't have default constructors for structs (and, according to TDPL, never will)? D does seem to generate hidden postblit constructors and destructors, though.

Don't forget that non-default constructors are fair game though. I agree that for this idiom it would be nice to have the default constructor guarantee execution of certain initializations.
 If I had to port a C++ project to D which made heavy use of this
 pattern, what would be the best way to do it? The only ways I see is
 either rewriting the code to use classes (which means writing
 constructors with explicit instantiation, more dereferences and heap
 usage leading to worse performance...), or implementing and calling
 pseudo-constructors in both B and C, and (most importantly) all places
 which "instantiate" C. Did I miss anything?

One simple technique I use is to write and use factory functions. They are particularly handy when C is also a template struct. Andrei
Aug 18 2010
prev sibling next sibling parent Michel Fortin <michel.fortin michelf.com> writes:
On 2010-08-18 06:13:25 -0400, Andrei Alexandrescu 
<SeeWebsiteForEmail erdani.org> said:

 http://www.informit.com/articles/article.aspx?p=1622265
 
 Andrei

Quoting: """ The most difficult scenario here is a class that has a struct as a member. If the struct has a destructor, it will be run non-deterministically—or possibly not at all. """ Or cause a race condition: <http://d.puremagic.com/issues/show_bug.cgi?id=4624> -- Michel Fortin michel.fortin michelf.com http://michelf.com/
Aug 18 2010
prev sibling next sibling parent Leandro Lucarella <luca llucax.com.ar> writes:
Walter Bright, el 18 de agosto a las 10:08 me escribiste:
 bearophile wrote:
Currently in the D2 GC there is no notion of pinned/unpinned class instances,
but eventually an attribute as  pinned may be added to D3, plus its related
semantics. It adds complexity to the language and it needs to interact with
the GC, so it will get useful as the D GC becomes more modern (with different
zones for newly allocated objects, etc).

There is no need for a pin attribute, the gc can determine if a class needs pinning or not.

As long as the precise heap scanning patch is applied (and much better if we can manage to scan the static data precisely too). Otherwise you simply just can't move stuff around because you don't know what is a pointer and what is not (thus you can't update pointer that point to moved stuff). -- Leandro Lucarella (AKA luca) http://llucax.com.ar/ ---------------------------------------------------------------------- GPG Key: 5F5A8D05 (F8CD F9A7 BF00 5431 4145 104C 949E BFB6 5F5A 8D05) ---------------------------------------------------------------------- Hoy estuvimos en el museo de antropología, pero yo voy a volver para estar por lo menos un día ahí adentro... es una locura, como Disney pero de indigenas -- Carla Lucarella (10/2008 contando de su viaje a México)
Aug 18 2010
prev sibling next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
Andrei Alexandrescu Wrote:

 http://www.informit.com/articles/article.aspx?p=1622265
 
 Andrei

I see you've mentioned the library function move() in the interview. I might have found an issue with move(), unless I missunderstood how it works. See my post here: http://news.gmane.org/gmane.comp.lang.d.general/cutoff=35852 Can't wait for part 3! :)
Aug 18 2010
prev sibling next sibling parent Leandro Lucarella <luca llucax.com.ar> writes:
Walter Bright, el 18 de agosto a las 12:25 me escribiste:
 Leandro Lucarella wrote:
Walter Bright, el 18 de agosto a las 10:08 me escribiste:
bearophile wrote:
Currently in the D2 GC there is no notion of pinned/unpinned class instances,
but eventually an attribute as  pinned may be added to D3, plus its related
semantics. It adds complexity to the language and it needs to interact with
the GC, so it will get useful as the D GC becomes more modern (with different
zones for newly allocated objects, etc).

class needs pinning or not.

As long as the precise heap scanning patch is applied (and much better if we can manage to scan the static data precisely too). Otherwise you simply just can't move stuff around because you don't know what is a pointer and what is not (thus you can't update pointer that point to moved stuff).

Hence the objects with ambiguous references to them get automatically pinned by the gc. I've implemented such a gc before, it works fine. It's called a "mostly copying collector".

Even when you say is true, the GC can automatically determine if something should be pinned when *EVERYTHING* is pinned, it's not very useful :)
 Besides, any scheme where you have to manually mark pinnable objects
 is doomed to have disastrously subtle and hard-to-find bugs.

I'm not arguing in favor of manual pinning, I completely agree is a bad idea. I'm just saying that, as things are, in D you can't implement a moving collector, because *ALL* the memory is pinned because if fully conservative. With the precise heap scanning patch for DMD the GC can automatically pin memory, because it has enough information to differentiate between real pointers and words which types are not really known, so a block can be moved *only* if is only pointed to by real pointers, otherwise is pinned because we can't update the words with unknown type if we moved that block. -- Leandro Lucarella (AKA luca) http://llucax.com.ar/ ---------------------------------------------------------------------- GPG Key: 5F5A8D05 (F8CD F9A7 BF00 5431 4145 104C 949E BFB6 5F5A 8D05) ---------------------------------------------------------------------- Hey you, out there in the cold Getting lonely, getting old Can you feel me?
Aug 19 2010
prev sibling next sibling parent Leandro Lucarella <luca llucax.com.ar> writes:
Walter Bright, el 18 de agosto a las 15:31 me escribiste:
 bearophile wrote:
Walter Bright:

There is no need for a pin attribute, the gc can determine if a class needs
 pinning or not.

The same is probably true for pure functions too, the compiler can determine what functions are pure and what are not pure. But the purpose of a pinned is that: 1) The default becomes unpinned. This is good for the GC, because moving memory around is good to compact the heap, etc. 2) The programmer states hir/her/his purpose, this is documentation, but it's an alive documentation because as with pure the compiler is able to determine if the attribute is used wrongly, and give a compile time error in such case.

The other problem with a pinned/notpinned object is the object itself cannot control who or how someone is pointing to it.

Exactly, manually pinning is really completely unpractical, the analogy between pure and pinned makes very little sense. I can see some very very weird use case where you want to arbitrarily mark some block pinned, but I think manual unpinning is just to dangerous to be useful. And for the former, you can easily force pinning by having a pointer to it in a portion of memory that is scanned conservatively. -- Leandro Lucarella (AKA luca) http://llucax.com.ar/ ---------------------------------------------------------------------- GPG Key: 5F5A8D05 (F8CD F9A7 BF00 5431 4145 104C 949E BFB6 5F5A 8D05) ---------------------------------------------------------------------- Y2K <Aztech_> hmm, nothing major has happend, what an anticlimax <CaPS> yeah <CaPS> really sucks <CaPS> I expected for Australia to sink into the sea or something <CaPS> but nnoooooooo
Aug 19 2010
prev sibling parent Leandro Lucarella <luca llucax.com.ar> writes:
Walter Bright, el 19 de agosto a las 13:08 me escribiste:
 Leandro Lucarella wrote:
With the precise heap scanning patch for DMD the GC can automatically
pin memory, because it has enough information to differentiate between
real pointers and words which types are not really known, so a block can
be moved *only* if is only pointed to by real pointers, otherwise is
pinned because we can't update the words with unknown type if we moved
that block.

I know. That's how a mostly copying collector works.

If you know, I guess you agree on the utility of the patch and the impossibility of implementing a mostly moving collector in D, so I hope you apply the patch eventually =) -- Leandro Lucarella (AKA luca) http://llucax.com.ar/ ---------------------------------------------------------------------- GPG Key: 5F5A8D05 (F8CD F9A7 BF00 5431 4145 104C 949E BFB6 5F5A 8D05) ---------------------------------------------------------------------- Hey you, standing in the road always doing what you're told, Can you help me?
Aug 19 2010