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digitalmars.D.bugs - [Issue 3112] New: Specification on what operations call the GC is missing

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3112

           Summary: Specification on what operations call the GC is
                    missing
           Product: D
           Version: 1.045
          Platform: Other
        OS/Version: All
            Status: NEW
          Keywords: spec
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: llucax gmail.com
            Blocks: 677


There are several languages constructs that rely on the GC and use it, like
array concatenation and appending. This operations are not properly documented.

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Jun 29 2009
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3112


Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla digitalmars.com
         Resolution|                            |FIXED


--- Comment #1 from Walter Bright <bugzilla digitalmars.com> 2010-11-10
00:25:48 PST ---
http://www.dsource.org/projects/phobos/changeset/2153

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Nov 10 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Petr Janda <janda.petr gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |janda.petr gmail.com


--- Comment #2 from Petr Janda <janda.petr gmail.com> 2010-12-21 23:40:16 PST
---
Why are things such as array concat and appending relying on GC? It looks to me
as that a lot of them could be accomplished without it.

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Dec 21 2010
prev sibling parent d-bugmail puremagic.com writes:
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Jonathan M Davis <jmdavisProg gmx.com> changed:

           What    |Removed                     |Added
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                 CC|                            |jmdavisProg gmx.com


--- Comment #3 from Jonathan M Davis <jmdavisProg gmx.com> 2010-12-22 00:03:29
PST ---
They use the GC for two reasons of which I am aware:

1. They potentially have to reallocate. That means allocating memory which
normally means using the GC. And since there's no way to tell something like ~=
to use malloc() (and potentially free()) instead of the GC, it _has_ to use the
GC.

2. As I understand it, the GC does some sort of voodoo to determine whether an
array actually has the capacity to increase its size in place. That's likely
going to have to figure out whether _other_ arrays refer to the memory
immediately after the end of the array, which would somehow involve looking at
the other arrays, which would require the GC, since one malloc-ed item knows
nothing about another malloc-ed item. The fact that you have slicing likely
complicates things a fair bit.

It would probably be possible to do array concatenation and appending without
the GC if arrays were not designed to use the GC (after all, vectors in C++ are
able to reallocate without the GC), but since they _do_ use the GC, they have
to use the GC for operations which would result in reallocating memory.

Actually, I believe that Steven pointed out on the list recently that you _can_
use appending with non-GCed dynamic arrays but that you have to maintain
references to the original before you append so that you can free that memory
if you need to. So, it _is_ possible, but it doesn't work very well.

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