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digitalmars.D - arrays of const, postblit and RefCounted

reply "monarch_dodra" <monarchdodra gmail.com> writes:
I investigating some weird behavior regarding arrays of const 
object. I'm not 100% sure what I'm observing, but it would appear 
that when adding objects to a const array, objects are not 
postblit-ed? Is this the expected behavior?

In this program, "S" is a struct that just prints when postblit 
is called:
//----
void main()
{
     S[] arr;
     foreach (i; 0 .. 5)
     {
         writeln(i);
         arr ~= S(i);
     }
}
//----
0
post
1
post
2
post
3
post
post
post
post
4
post
//----
Here, we can clearly see each element being postblit inserted. We 
can also see the array re-locating.

However, if we change "S[] arr;" to "const(S)[] arr;", then the 
output becomes:
//----
0
1
2
3
4
//----

Strange... right?

I was actually investigating the issue when trying to do a const 
array of refcounted. It was behaving scary weird...:

//----
alias RCI = RefCounted!(int, RefCountedAutoInitialize.no);
void main()
{
     const(RCI)[] arr;
     foreach (i; 0 .. 3)
     {
         foreach (j; 0 .. i)
             writefln("pay[%s]: %s", j, arr[j].refCountedPayload);

         auto a = const(RCI)(i);
         writefln("declared a: %s", a.refCountedPayload);

         foreach (j; 0 .. i)
             writefln("pay[%s] before: %s", j, 
arr[j].refCountedPayload);

         arr ~= a;

         foreach (j; 0 .. i + 1)
             writefln("pay[%s] after: %s", j, 
arr[j].refCountedPayload);
         writeln();
     }
     writeln("after");
     foreach (i; 0 .. 3)
         writeln("pay: ", arr[i].refCountedPayload);
}
//----
declared a: 0
pay[0] after: 0

pay[0]: 0
declared a: 1
pay[0] before: 1
pay[0] after: 1
pay[1] after: 1

pay[0]: 0
pay[1]: 0
declared a: 2
pay[0] before: 2
pay[1] before: 2
pay[0] after: 2
pay[1] after: 2
pay[2] after: 2

after
pay: 0
pay: 0
pay: 0
//----

See!?

The sole fact of declaring a on the stack modifies the values of 
all the elements in the array... And as soon as it goes out of 
scope, they all become 0 :/

The weirdest part (IMO), is that since "RefCountedAutoInitialize 
== no", the value "0" is not a result of an auto initialize: It 
is the actual allocated value of the RCI that is changing...

Changing it to non const "fixes" this, but I really don't even 
begin to fathom what is happening...

Thoughts?
Nov 29 2012
next sibling parent reply "monarch_dodra" <monarchdodra gmail.com> writes:
On Thursday, 29 November 2012 at 15:14:51 UTC, monarch_dodra 
wrote:

 Thoughts?


I give up:

//----
     RCI[] arr3 = [RCI(0), RCI(1)];
     foreach(i; 0 .. 2)
         assert(arr3[i] == i);
//----

This asserts '-_-

The worst part is that I can *see* in the constructor that the 
refcounted store points to an memory location, and that that 
memory location's value gets changed to 0...
Nov 29 2012
parent Dmitry Olshansky <dmitry.olsh gmail.com> writes:
11/29/2012 8:16 PM, monarch_dodra пишет:

 On Thursday, 29 November 2012 at 15:14:51 UTC, monarch_dodra wrote:

 Thoughts?


 I give up:

 //----
      RCI[] arr3 = [RCI(0), RCI(1)];
      foreach(i; 0 .. 2)
          assert(arr3[i] == i);
 //----


I think I've seen it before. The problem is in the array literal.
http://d.puremagic.com/issues/show_bug.cgi?id=8740


 This asserts '-_-

 The worst part is that I can *see* in the constructor that the
 refcounted store points to an memory location, and that that memory
 location's value gets changed to 0...



-- 
Dmitry Olshansky
Nov 29 2012
prev sibling next sibling parent "bearophile" <bearophileHUGS lycos.com> writes:
monarch_dodra:


 However, if we change "S[] arr;" to "const(S)[] arr;", then the 
 output becomes:
 //----
 0
 1
 2
 3
 4
 //----

 Strange... right?


I think it's a known problem of the postblit. It was discussed 
recently.

Bye,
bearophile
Nov 29 2012
prev sibling parent reply "Maxim Fomin" <maxim maxim-fomin.ru> writes:
On Thursday, 29 November 2012 at 15:14:51 UTC, monarch_dodra 
wrote:

 I investigating some weird behavior regarding arrays of const 
 object. I'm not 100% sure what I'm observing, but it would 
 appear that when adding objects to a const array, objects are 
 not postblit-ed? Is this the expected behavior?

 <skipped>


In windows it acts like you describe (no postblit for 
const(S)arr[]), but in linux it calls postblit 
http://dpaste.dzfl.pl/e63e5aa3.
Nov 29 2012
parent "monarch_dodra" <monarchdodra gmail.com> writes:
On Thursday, 29 November 2012 at 18:42:17 UTC, Maxim Fomin wrote:

 On Thursday, 29 November 2012 at 15:14:51 UTC, monarch_dodra 
 wrote:

 I investigating some weird behavior regarding arrays of const 
 object. I'm not 100% sure what I'm observing, but it would 
 appear that when adding objects to a const array, objects are 
 not postblit-ed? Is this the expected behavior?

 <skipped>


 In windows it acts like you describe (no postblit for 
 const(S)arr[]), but in linux it calls postblit 
 http://dpaste.dzfl.pl/e63e5aa3.


Well shit.

It also correctly runs my "RCI[] arr = [RCI(0), RCI(1)];" test.

http://dpaste.dzfl.pl/6baa678d

Gonna see what's in the bug reports then.
Nov 29 2012