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digitalmars.D - A Tango Fibers question and a functional programming anecdote.

reply downs <default_357-line yahoo.de> writes:
Here's a question to the tango devs.
I've been developing my own stackthreads (Fibers basically) library for
a while now, and finally got it working a few days ago.

Then we did some speed tests and discovered that it was about twice as
slow as Tango's Fiber implementation.

This prompted me to dig into the Fibers sourcecode, where I discovered
that Fibers doesn't backup ECX/EDX on context switch, and the FP
registers only on windows.

Now I am confused.

Could a knowledgeable tango dev kindly shed light on this issue? Why
isn't it necessary to save all registers on a context switch?

----
Now for the anecdote.
Today, at five in the morning, I wrote what I believe to be the first
purely functional D code with as little redundancy as possible in the
language.


 ["Load ", "Prefetch ", "Prefetch "] /zip/ ([0, 1, 2] /map/ (&info



&concat!(string) /zip/ [&update, &prefetch /fix/ (currentStrip-1),
&prefetch /fix/ (currentStrip-2)] /map/ &Pool.addTask;



So I looked at it, and for some _strange_ reason my eyes suddenly
started bleeding heavily.
That's when I knew I had overdone it on the templates again.
:)


PS: Here's the same code with some line breaks. But where's the fun in that?


 ["Load ", "Prefetch ", "Prefetch "] /zip/ (
   [0, 1, 2] /map/ (
     &info /rfix/ currentComic /fix/ (
       &subtract!(int) /fix/ currentStrip
       )
     )
   )
   /map/ &concat!(string) /zip/ [
     &update,
     &prefetch /fix/ (currentStrip-1),
     &prefetch /fix/ (currentStrip-2)
   ] /map/ &Pool.addTask;






 Oct 27 2007



 next sibling parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com>  writes:


"downs" <default_357-line yahoo.de> wrote in message 
news:fg15ev$12uh$1 digitalmars.com...

 Here's a question to the tango devs.
 I've been developing my own stackthreads (Fibers basically) library for
 a while now, and finally got it working a few days ago.

 Then we did some speed tests and discovered that it was about twice as
 slow as Tango's Fiber implementation.

 This prompted me to dig into the Fibers sourcecode, where I discovered
 that Fibers doesn't backup ECX/EDX on context switch, and the FP
 registers only on windows.

 Now I am confused.

 Could a knowledgeable tango dev kindly shed light on this issue? Why
 isn't it necessary to save all registers on a context switch?



I'm not knowledgeable, but you said ECX/EDX and it triggered something in my 
brain.  Sure enough, according to the D 1.0 ABI, "EAX, ECX, EDX are scratch 
registers and can be destroyed by a function."  So they don't have to be 
preserved because you're allowed to do anything with them.

As for nothing but ST(0-7) being preserved on Windows.. no clue.


 ["Load ", "Prefetch ", "Prefetch "] /zip/ ([0, 1, 2] /map/ (&info



 &concat!(string) /zip/ [&update, &prefetch /fix/ (currentStrip-1),
 &prefetch /fix/ (currentStrip-2)] /map/ &Pool.addTask;




 ["Load ", "Prefetch ", "Prefetch "] /zip/ (
   [0, 1, 2] /map/ (
     &info /rfix/ currentComic /fix/ (
       &subtract!(int) /fix/ currentStrip
       )
     )
   )
   /map/ &concat!(string) /zip/ [
     &update,
     &prefetch /fix/ (currentStrip-1),
     &prefetch /fix/ (currentStrip-2)
   ] /map/ &Pool.addTask;






Why/how do you write code like this?  Is it some kind of thing in your brain 
that makes you think about everything inside out?  Stop it.  Please.  For 
all our brains' sakes. 



 Oct 27 2007



  parent reply downs <default_357-line yahoo.de>  writes:


Jarrett Billingsley wrote:

 I'm not knowledgeable, but you said ECX/EDX and it triggered something in my 
 brain.  Sure enough, according to the D 1.0 ABI, "EAX, ECX, EDX are scratch 
 registers and can be destroyed by a function."  So they don't have to be 
 preserved because you're allowed to do anything with them.
 



Removed the push for ECX and EDX ( the others are used internally ). It
seems to work. Many thanks! :)

Still runs somewhat slower than Fibers, though. I can't imagine why.
Also, oddly, GDC doesn't allow me to push EBP in -O mode and D inline
assembly. Works in native GCC assembly. *Very* odd.


 As for nothing but ST(0-7) being preserved on Windows.. no clue.
 



Aww. Still thanks for answering. I'm sure somebody will know it.


 ["Load ", "Prefetch ", "Prefetch "] /zip/ ([0, 1, 2] /map/ (&info



 &concat!(string) /zip/ [&update, &prefetch /fix/ (currentStrip-1),
 &prefetch /fix/ (currentStrip-2)] /map/ &Pool.addTask;




 ["Load ", "Prefetch ", "Prefetch "] /zip/ (
   [0, 1, 2] /map/ (
     &info /rfix/ currentComic /fix/ (
       &subtract!(int) /fix/ currentStrip
       )
     )
   )
   /map/ &concat!(string) /zip/ [
     &update,
     &prefetch /fix/ (currentStrip-1),
     &prefetch /fix/ (currentStrip-2)
   ] /map/ &Pool.addTask;






 Why/how do you write code like this?  Is it some kind of thing in your brain 
 that makes you think about everything inside out?  Stop it.  Please.  For 
 all our brains' sakes. 
 
 



:evil cackle:
Braaaaaaaaaaaaaaains!


Actually, it started out with a piece of code that looked like this


 Pool.addTask("Load "~info(), &update);
 Pool.addTask("Prefetch "~info(), &update);
 Pool.addTask("Prefetch "~info(), &update);



Clearly, the addTask is redundant here.
I replaced it with


 [stuple("Load "~info(), &update), stuple...] /map/ &Pool.addTask;



Somebody in IRC pointed out that the stuple was redundant.
He must feel horrible for indirectly causing this.


 ["Load "~info, ...] /zip/ [&update, ...] /map/ &Pool.addTask;



Then I noticed the info calls were also redundant. It went kinda out of
control after that. You know the result. :)

 --downs



 Oct 28 2007



 next sibling parent  Daniel Keep <daniel.keep.lists gmail.com>  writes:


downs wrote:

 Jarrett Billingsley wrote:

 ...
 As for nothing but ST(0-7) being preserved on Windows.. no clue.



 Aww. Still thanks for answering. I'm sure somebody will know it.



I think this might be it (from the ABI):

"The FPU stack must be empty when calling a function."

So when it calls the function, the caller will have emptied the FP
stack, so there's nothing *in* ST(0-7) to save.


 ...
 

 ["Load "~info, ...] /zip/ [&update, ...] /map/ &Pool.addTask;



 Then I noticed the info calls were also redundant. It went kinda out of
 control after that. You know the result. :)
 
  --downs



You're my hero, downs.

	-- Daniel



 Oct 28 2007



prev sibling  parent  "Jarrett Billingsley" <kb3ctd2 yahoo.com>  writes:


"downs" <default_357-line yahoo.de> wrote in message 
news:fg1qhp$22m6$1 digitalmars.com...


 Actually, it started out with a piece of code that looked like this


 Pool.addTask("Load "~info(), &update);
 Pool.addTask("Prefetch "~info(), &update);
 Pool.addTask("Prefetch "~info(), &update);






There's an idea for a language feature (off-the-wall and will never get in, 
but regardless!)

class Pool
{
    void addTask(char[][] names..., void delegate() dgs...)
    {
        // names and dgs should be the same length
        // pairs are in names[i] and dgs[i]
    }
}

Pool.addTask("Load " ~ info(), &update, "Prefetch " ~ info(), &update);

Heee.

I don't see, though, why you couldn't do

void addTask(void delegate()[char[]] tasks) { ... }

Pool.addTask(["Load " ~ info() : &update, "Prefetch " ~ info() : &update]);


 Clearly, the addTask is redundant here.
 I replaced it with


 [stuple("Load "~info(), &update), stuple...] /map/ &Pool.addTask;



 Somebody in IRC pointed out that the stuple was redundant.
 He must feel horrible for indirectly causing this.


 ["Load "~info, ...] /zip/ [&update, ...] /map/ &Pool.addTask;



 Then I noticed the info calls were also redundant. It went kinda out of
 control after that. You know the result. :)



Redundancy is not much to worry about, especially if the result of removing 
it is entirely unreadable. 



 Oct 28 2007



prev sibling next sibling parent  Don Clugston <dac nospam.com.au>  writes:


downs wrote:

 Here's a question to the tango devs.
 I've been developing my own stackthreads (Fibers basically) library for
 a while now, and finally got it working a few days ago.
 
 Then we did some speed tests and discovered that it was about twice as
 slow as Tango's Fiber implementation.
 
 This prompted me to dig into the Fibers sourcecode, where I discovered
 that Fibers doesn't backup ECX/EDX on context switch, and the FP
 registers only on windows.
 
 Now I am confused.
 
 Could a knowledgeable tango dev kindly shed light on this issue? Why
 isn't it necessary to save all registers on a context switch?
 
 ----
 Now for the anecdote.
 Today, at five in the morning, I wrote what I believe to be the first
 purely functional D code with as little redundancy as possible in the
 language.
 

 ["Load ", "Prefetch ", "Prefetch "] /zip/ ([0, 1, 2] /map/ (&info



 &concat!(string) /zip/ [&update, &prefetch /fix/ (currentStrip-1),
 &prefetch /fix/ (currentStrip-2)] /map/ &Pool.addTask;
 
 So I looked at it, and for some _strange_ reason my eyes suddenly
 started bleeding heavily.
 That's when I knew I had overdone it on the templates again.
 :)



In my best Hercules Grytpype-Thynne voice:
"You silly, twisted boy."

http://www.thegoonshow.net/quotes.asp



 Oct 28 2007



prev sibling next sibling parent reply Robert Fraser <fraserofthenight gmail.com>  writes:


downs Wrote:


 ["Load ", "Prefetch ", "Prefetch "] /zip/ ([0, 1, 2] /map/ (&info



 &concat!(string) /zip/ [&update, &prefetch /fix/ (currentStrip-1),
 &prefetch /fix/ (currentStrip-2)] /map/ &Pool.addTask;



Ewwww!

That whole create-your-own infix operator thing *is* cool, no doubt, but IMO,
it reduces readability. To me:

map(array, &func);

... is more readable than...

array /map/ &func;

... but maybe that's because I've never actually done any functional
programming.



 Oct 28 2007



  parent  Bill Baxter <dnewsgroup billbaxter.com>  writes:


Robert Fraser wrote:

 downs Wrote:
 

 ["Load ", "Prefetch ", "Prefetch "] /zip/ ([0, 1, 2] /map/ (&info



 &concat!(string) /zip/ [&update, &prefetch /fix/ (currentStrip-1),
 &prefetch /fix/ (currentStrip-2)] /map/ &Pool.addTask;



 Ewwww!
 
 That whole create-your-own infix operator thing *is* cool, no doubt, but IMO,
it reduces readability. To me:
 
 map(array, &func);
 
 ... is more readable than...
 
 array /map/ &func;
 
 ... but maybe that's because I've never actually done any functional
programming.



The use of infix operators is unrelated to functional programming.  Lisp 
doesn't have infix operators, for instance.  map(array, &func) is every 
bit as "functional" as  array /map/ &func.  Or array.map(&func) for that 
matter.  The functional style part comes from hiding the explicit 
procedural steps taken by the computer in functions like 'map', and by 
treating functions like 'func' more as data than code.

--bb



 Oct 28 2007



prev sibling next sibling parent reply BCS <ao pathlink.com>  writes:


Reply to Downs,


 ["Load ", "Prefetch ", "Prefetch "] /zip/ (
 [0, 1, 2] /map/ (
 &info /rfix/ currentComic /fix/ (
 &subtract!(int) /fix/ currentStrip
 )
 )
 )
 /map/ &concat!(string) /zip/ [
 &update,
 &prefetch /fix/ (currentStrip-1),
 &prefetch /fix/ (currentStrip-2)
 ] /map/ &Pool.addTask;






how the heck is that parsing?? Is the /map/ actualy this:

(A / B) / C; ??



 Oct 28 2007



  parent reply BCS <ao pathlink.com>  writes:


Reply to Benjamin,


 Reply to Downs,
 

 ["Load ", "Prefetch ", "Prefetch "] /zip/ (
 [0, 1, 2] /map/ (
 &info /rfix/ currentComic /fix/ (
 &subtract!(int) /fix/ currentStrip
 )
 )
 )
 /map/ &concat!(string) /zip/ [
 &update,
 &prefetch /fix/ (currentStrip-1),
 &prefetch /fix/ (currentStrip-2)
 ] /map/ &Pool.addTask;






 
 (A / B) / C; ??
 



BTW if that is what you are doing, I may be force to do something totally 
EVIL to reclaim some ground in the "does nasty things with D" ranking. I 
have a few ideas though....  }:-)  (BBBBWWWWAAAA HAA Haa haaa.....)



 Oct 28 2007



  parent reply Daniel Keep <daniel.keep.lists gmail.com>  writes:


BCS wrote:

 Reply to Benjamin,
 ...

 how the heck is that parsing?? Is the /map/ actualy this:

 (A / B) / C; ??



 BTW if that is what you are doing, I may be force to do something
 totally EVIL to reclaim some ground in the "does nasty things with D"
 ranking. I have a few ideas though....  }:-)  (BBBBWWWWAAAA HAA Haa
 haaa.....)



IIRC, map is basically defined like this:

struct map
{
  static map_ opDiv_r(T)(some_array_type!(T));
}

struct map_
{
  some_array_type!(T) opDiv(T)(some_delegate_type!(T));
}

Or something similar.

	-- Daniel



 Oct 28 2007



  parent reply downs <default_357-line yahoo.de>  writes:


Daniel Keep wrote:

 
 BCS wrote:

 Reply to Benjamin,
 ...

 how the heck is that parsing?? Is the /map/ actualy this:

 (A / B) / C; ??



 totally EVIL to reclaim some ground in the "does nasty things with D"
 ranking. I have a few ideas though....  }:-)  (BBBBWWWWAAAA HAA Haa
 haaa.....)






Looking forward to it! :)
The world needs more weird and disturbing things. Shake it up.


 
 IIRC, map is basically defined like this:
 
 struct map
 {
   static map_ opDiv_r(T)(some_array_type!(T));
 }
 
 struct map_
 {
   some_array_type!(T) opDiv(T)(some_delegate_type!(T));
 }
 
 Or something similar.
 
 	-- Daniel



Yes exactly; though I have all the ugliness packed around in a template.


Quote from the respective file:

 mixin(Operator!("map", "
   static if (is(ReturnType!(RHS)==void)) {
     foreach (ref entry; lhs) rhs(mixin(Value!(ElemType!(LHS), RHS,




   } else {
     auto res=new ReturnType!(RHS)[lhs.length];
     foreach (id, ref entry; res)




     return res;
   }
 "));






 Oct 28 2007



  parent reply Bill Baxter <dnewsgroup billbaxter.com>  writes:


downs wrote:

 Daniel Keep wrote:

 BCS wrote:

 Reply to Benjamin,
 ...

 how the heck is that parsing?? Is the /map/ actualy this:

 (A / B) / C; ??



 totally EVIL to reclaim some ground in the "does nasty things with D"
 ranking. I have a few ideas though....  }:-)  (BBBBWWWWAAAA HAA Haa
 haaa.....)






 Looking forward to it! :)
 The world needs more weird and disturbing things. Shake it up.
 

 IIRC, map is basically defined like this:

 struct map
 {
   static map_ opDiv_r(T)(some_array_type!(T));
 }

 struct map_
 {
   some_array_type!(T) opDiv(T)(some_delegate_type!(T));
 }

 Or something similar.

 	-- Daniel



 Yes exactly; though I have all the ugliness packed around in a template.



Does it compile down to the same code as just a plain call to a map() 
function?  (Or is there some other benefit that justifies the extra 
runtime cost and loss of readability?)

--bb



 Oct 29 2007



  parent  downs <default_357-line yahoo.de>  writes:


Bill Baxter wrote:

 
 Does it compile down to the same code as just a plain call to a map()
 function?  (Or is there some other benefit that justifies the extra
 runtime cost and loss of readability?)
 
 --bb



Loss of readability is debatable. Personally I like it better, or else I
wouldn't use it. :)
The runtime cost might not be as high as you expect. Let us do a test.


 module test12;
 import std.stdio;
 import tools.base, tools.functional, tools.log;

 int add(int a, int b) { return a+b; }

 mixin(Operator!("add3", "return lhs+rhs;"));

 void main() {
   const long count=1_000_000_000;
   long test;
   int delegate(int, int) add1=(int a, int b) { return add(a, b); };
   int function(int, int) add2=&add;
   logln("Function: ", time({ for (int i=0; i<count; ++i) test+=add(0,




   logln("Delegate function: ", time({ for (int i=0; i<count; ++i)




   logln("Function ... function: ", time({ for (int i=0; i<count; ++i)




   logln("Infix function: ", time({ for (int i=0; i<count; ++i) test+=0




 }



The results:


 gentoo-pc ~/d $ gdc test12.d -o test12 -O3 -frelease -Itools




 /--[ Main Thread ]------
 | Function: 0 -test 1000000000
 | Delegate function: 7234 -test 2000000000
 | Function ... function: 6415 -test -1294967296
 | Infix function: 1501 -test -294967296
 \-----------------------------



Hm ... interesting.
I had expected the infix function to be inlined as well as the straight
function. Ah well. Four times the speed of an un-inlined function is
good enough for me. :)



 Oct 29 2007



prev sibling  parent  bearophile <bearophile lycos.com>  writes:


downs Wrote:

 ["Load ", "Prefetch ", "Prefetch "] /zip/ ([0, 1, 2] /map/ (&info



 &concat!(string) /zip/ [&update, &prefetch /fix/ (currentStrip-1),
 &prefetch /fix/ (currentStrip-2)] /map/ &Pool.addTask;



I too have developed a large functional-style lib for D, but I think D needs a
bit more built-in support for it (the first class functions, allowing a better
syntax, etc) and you need to program in a more tidy way :-)

bearophile



 Oct 29 2007