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digitalmars.D.learn - Quick int pointer allocation question

reply "monarch_dodra" <monarchdodra gmail.com> writes:
This is going to be quick: Is it possible to allocate and 
initialize an int in the same line?

int* p = new int(5);

I haven't found a way to 1 liner it. Is it possible?
Do I have to two liner it?

int* p = new int();
*p = 5;

Thanks.
Sep 14 2012
next sibling parent reply "monarch_dodra" <monarchdodra gmail.com> writes:
On Friday, 14 September 2012 at 09:20:03 UTC, monarch_dodra wrote:

 This is going to be quick: Is it possible to allocate and 
 initialize an int in the same line?

 int* p = new int(5);

 I haven't found a way to 1 liner it. Is it possible?
 Do I have to two liner it?

 int* p = new int();
 *p = 5;

 Thanks.


Or dup a pointer to an int for that matter:

int* p1 = ... ;
int* p2 = p1.dup;

?
Sep 14 2012
parent reply "monarch_dodra" <monarchdodra gmail.com> writes:
On Friday, 14 September 2012 at 09:22:09 UTC, monarch_dodra wrote:

 On Friday, 14 September 2012 at 09:20:03 UTC, monarch_dodra 
 wrote:

 This is going to be quick: Is it possible to allocate and 
 initialize an int in the same line?

 int* p = new int(5);

 I haven't found a way to 1 liner it. Is it possible?
 Do I have to two liner it?

 int* p = new int();
 *p = 5;

 Thanks.


 Or dup a pointer to an int for that matter:

 int* p1 = ... ;
 int* p2 = p1.dup;

 ?


Whilst I'm on the subject of questions, how does one allocate, 
but bypassing the extra memcpy of T.init? Is this possible?
Sep 14 2012
parent reply David <d dav1d.de> writes:
 Whilst I'm on the subject of questions, how does one allocate, but
 bypassing the extra memcpy of T.init? Is this possible?


int x = void;

http://dpaste.dzfl.pl/24c1baa9
Sep 14 2012
parent reply "monarch_dodra" <monarchdodra gmail.com> writes:
On Friday, 14 September 2012 at 10:33:47 UTC, David wrote:

 Whilst I'm on the subject of questions, how does one allocate, 
 but
 bypassing the extra memcpy of T.init? Is this possible?


 int x = void;

 http://dpaste.dzfl.pl/24c1baa9


Hum, but that is a stack allocated variable.

What about:

--------
struct S { }
void main()
{
     S* ps = new S(void); //? doesn't work
}

On Friday, 14 September 2012 at 10:37:56 UTC, Jonathan M Davis 
wrote:

 On Friday, September 14, 2012 11:20:16 monarch_dodra wrote:

 This is going to be quick: Is it possible to allocate and
 initialize an int in the same line?
 
 int* p = new int(5);
 
 I haven't found a way to 1 liner it. Is it possible?


 Nope. Though I think that it should be.


 Do I have to two liner it?
 
 int* p = new int();
 *p = 5;


 Yep. Though I have a pull request which will make it so that 
 you can do

 auto p = makeNew!int(5);

 https://github.com/D-Programming-Language/phobos/pull/756

 - Jonathan M Davis


Thanks. Glad we have a library solution, but that's the kind of 
thing that should work out of the box I think.
Sep 14 2012
parent reply Jacob Carlborg <doob me.com> writes:
On 2012-09-14 12:52, monarch_dodra wrote:


 int x = void;

 http://dpaste.dzfl.pl/24c1baa9


 Hum, but that is a stack allocated variable.


Perhaps using GC.malloc?

-- 
/Jacob Carlborg
Sep 14 2012
parent reply "monarch_dodra" <monarchdodra gmail.com> writes:
On Friday, 14 September 2012 at 11:17:55 UTC, Jacob Carlborg 
wrote:

 On 2012-09-14 12:52, monarch_dodra wrote:


 int x = void;

 http://dpaste.dzfl.pl/24c1baa9


 Hum, but that is a stack allocated variable.


 Perhaps using GC.malloc?


Hum, apparently, there is a second (default aka-hidden) argument 
that is a bitmask applied to the allocated memory. So not much 
gain there.

I'm allocating an array of 500_000 ulongs, and afterwards, I'm 
initializing them all "by hand", making the default allocation 
useless.

I'm not going to lose any sleep over this, but there is no way in 
D to get (garbage collected) un-initialized memory/allocations?
Sep 14 2012
next sibling parent "Simen Kjaeraas" <simen.kjaras gmail.com> writes:
On Fri, 14 Sep 2012 16:27:55 +0200, monarch_dodra <monarchdodra gmail.com>  
wrote:


 On Friday, 14 September 2012 at 11:17:55 UTC, Jacob Carlborg wrote:

 On 2012-09-14 12:52, monarch_dodra wrote:


 int x = void;

 http://dpaste.dzfl.pl/24c1baa9


 Hum, but that is a stack allocated variable.


 Perhaps using GC.malloc?


 Hum, apparently, there is a second (default aka-hidden) argument that is  
 a bitmask applied to the allocated memory. So not much gain there.

 I'm allocating an array of 500_000 ulongs, and afterwards, I'm  
 initializing them all "by hand", making the default allocation useless.

 I'm not going to lose any sleep over this, but there is no way in D to  
 get (garbage collected) un-initialized memory/allocations?


What's wrong with GC.malloc? The bitmask is there to... well, many things.
Pass it BlkAttr.NO_SCAN to ensure memory is not initialized. I think that's
all what's needed.

-- 
Simen
Sep 14 2012
prev sibling next sibling parent reply "bearophile" <bearophileHUGS lycos.com> writes:
monarch_dodra:


 I'm allocating an array of 500_000 ulongs, and afterwards, I'm 
 initializing them all "by hand", making the default allocation 
 useless.


In std.array there are two functions to avoid a double 
initialization, mostly to be used for nonreference data.

Bye,
bearophile
Sep 14 2012
parent "Chris Cain" <clcain uncg.edu> writes:
On Friday, 14 September 2012 at 18:14:54 UTC, bearophile wrote:

 monarch_dodra:


 I'm allocating an array of 500_000 ulongs, and afterwards, I'm 
 initializing them all "by hand", making the default allocation 
 useless.


 In std.array there are two functions to avoid a double 
 initialization, mostly to be used for nonreference data.

 Bye,
 bearophile


http://dlang.org/phobos/std_array.html#uninitializedArray

and

http://dlang.org/phobos/std_array.html#minimallyInitializedArray
Sep 14 2012
prev sibling parent reply "monarch_dodra" <monarchdodra gmail.com> writes:
On Friday, 14 September 2012 at 14:27:43 UTC, monarch_dodra wrote:

 On Friday, 14 September 2012 at 11:17:55 UTC, Jacob Carlborg 
 wrote:

 Perhaps using GC.malloc?


 Hum, apparently, there is a second (default aka-hidden) 
 argument that is a bitmask applied to the allocated memory. So 
 not much gain there.

 I'm allocating an array of 500_000 ulongs, and afterwards, I'm 
 initializing them all "by hand", making the default allocation 
 useless.

 I'm not going to lose any sleep over this, but there is no way 
 in D to get (garbage collected) un-initialized 
 memory/allocations?


Never mind, I misread the doc. The bitmask is not memcopied, it 
is actually just a mask of options, so GC works perfectly.

Anybody know what the attribute "FINALIZE" (Finalize the data in 
this block on collect) means?

On Friday, 14 September 2012 at 18:14:54 UTC, bearophile wrote:

 monarch_dodra:


 I'm allocating an array of 500_000 ulongs, and afterwards, I'm 
 initializing them all "by hand", making the default allocation 
 useless.


 In std.array there are two functions to avoid a double 
 initialization, mostly to be used for nonreference data.

 Bye,
 bearophile


I was looking for those actually, but I was looking in 
std.algorithm...

Thanks
Sep 14 2012
parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Fri, 14 Sep 2012 15:23:40 -0400, monarch_dodra <monarchdodra gmail.com>  
wrote:


 Anybody know what the attribute "FINALIZE" (Finalize the data in this  
 block on collect) means?


Don't use it.

It specifies that the block is a D class instance, and so has a vtable  
with a finalizer referenced therein.

Obviously an int does not have that.

-Steve
Sep 14 2012
prev sibling next sibling parent Jonathan M Davis <jmdavisProg gmx.com> writes:
On Friday, September 14, 2012 11:20:16 monarch_dodra wrote:

 This is going to be quick: Is it possible to allocate and
 initialize an int in the same line?
 
 int* p = new int(5);
 
 I haven't found a way to 1 liner it. Is it possible?


Nope. Though I think that it should be.


 Do I have to two liner it?
 
 int* p = new int();
 *p = 5;


Yep. Though I have a pull request which will make it so that you can do

auto p = makeNew!int(5);

https://github.com/D-Programming-Language/phobos/pull/756

- Jonathan M Davis
Sep 14 2012
prev sibling next sibling parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Fri, 14 Sep 2012 05:20:16 -0400, monarch_dodra <monarchdodra gmail.com>  
wrote:


 This is going to be quick: Is it possible to allocate and initialize an  
 int in the same line?

 int* p = new int(5);

 I haven't found a way to 1 liner it. Is it possible?
 Do I have to two liner it?

 int* p = new int();
 *p = 5;


int *p = [5].ptr;

-Steve
Sep 14 2012
parent reply "monarch_dodra" <monarchdodra gmail.com> writes:
On Friday, 14 September 2012 at 14:33:51 UTC, Steven 
Schveighoffer wrote:

 On Fri, 14 Sep 2012 05:20:16 -0400, monarch_dodra 
 <monarchdodra gmail.com> wrote:


 This is going to be quick: Is it possible to allocate and 
 initialize an int in the same line?

 int* p = new int(5);

 I haven't found a way to 1 liner it. Is it possible?
 Do I have to two liner it?

 int* p = new int();
 *p = 5;


 int *p = [5].ptr;

 -Steve


Fancy!

Thankyou.
Sep 14 2012
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
monarch_dodra:


 int *p = [5].ptr;

 -Steve




But see this benchmark:


void main() {
     auto pointers = new int*[1_000_000];
     foreach (int i, ref p; pointers)
         p = [i].ptr;
     foreach (i; 0U .. 4_000_000_000U) {}
}


On my 32 bit system its RAM commit is about 23 MB. The pointers 
array takes about 4 MB. This means each "int" takes about 19 
bytes of heap RAM instead of 4. Each int allocates some data 
(capacity) to extend the array.

Bye,
bearophile
Sep 14 2012
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Fri, 14 Sep 2012 13:03:37 -0400, bearophile <bearophileHUGS lycos.com>  
wrote:


 monarch_dodra:


 int *p = [5].ptr;

 -Steve




 But see this benchmark:


 void main() {
      auto pointers = new int*[1_000_000];
      foreach (int i, ref p; pointers)
          p = [i].ptr;
      foreach (i; 0U .. 4_000_000_000U) {}
 }


 On my 32 bit system its RAM commit is about 23 MB. The pointers array  
 takes about 4 MB. This means each "int" takes about 19 bytes of heap RAM  
 instead of 4. Each int allocates some data (capacity) to extend the  
 array.


That has nothing to do with using array literals -- it has to do with the  
fact that the minimum heap block is 16-bytes (or 4 ints wide).  Extra 3  
bytes is probably for overhead and static data.

If instead of p = [i].ptr; you did p = new int; *p = i;

You would get the same exact behavior.

No way around this, unless you want to do custom allocators.

-Steve
Sep 14 2012
parent "bearophile" <bearophileHUGS lycos.com> writes:
Steven Schveighoffer:


 it has to do with the fact that the minimum heap block is 
 16-bytes
 (or 4 ints wide).  Extra 3 bytes is probably for overhead and 
 static data.

 If instead of p = [i].ptr; you did p = new int; *p = i;

 You would get the same exact behavior.

 No way around this, unless you want to do custom allocators.


Right, maybe you told me the same thing lot of time ago. Thank 
you for saying such things again. 16 bytes are a lot, so there's 
not a lot of point in creating very small trees nodes :-)

Bye,
bearophile
Sep 14 2012
prev sibling parent "Maxim Fomin" <maxim maxim-fomin.ru> writes:
On Friday, 14 September 2012 at 09:20:03 UTC, monarch_dodra wrote:

 This is going to be quick: Is it possible to allocate and 
 initialize an int in the same line?

 int* p = new int(5);

 I haven't found a way to 1 liner it. Is it possible?
 Do I have to two liner it?

 int* p = new int();
 *p = 5;

 Thanks.


Firstly I thought this thread is purely about syntax. However, 
after rereading I think it is about problem of allocation on GC 
heap without default initialization. If I understood it right, 
possible solution is:

struct S
{
    ulong[500_000] array = void;
    void load(ulong value)
    {
       foreach (i, ref ulong v; array)
       {
          array[i] = value;
       }
    }
}

void main()
{
    // int* p = new int, x = ((*p=5) == 5) ? null : null;
    // assert(*p == 5);
    auto s = new S;
    s.load(5);
}
Sep 14 2012