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digitalmars.D - GCAllocator goodAllocSize?

reply Steven Schveighoffer <schveiguy yahoo.com> writes:
import std.experimental.allocator.gc_allocator;

void main()
{
    //GCAllocator.instance.goodAllocSize(3000); // error
    writeln(theAllocator.goodAllocSize(3000)); // 3008, should be 4096
}

This is known info, why is it not available? Is there a reason this 
needs to be inaccurate? I can create a PR if desired.

-Steve
Jan 29 2016
parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
On 1/29/16 9:52 PM, Steven Schveighoffer wrote:

 import std.experimental.allocator.gc_allocator;

 void main()
 {
     //GCAllocator.instance.goodAllocSize(3000); // error
     writeln(theAllocator.goodAllocSize(3000)); // 3008, should be 4096
 }

 This is known info, why is it not available? Is there a reason this
 needs to be inaccurate? I can create a PR if desired.


There's no need, I just put in reasonable conservative defaults. Please 
do follow up - thanks! -- Andrei
Jan 30 2016
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 1/30/16 12:41 PM, Andrei Alexandrescu wrote:

 On 1/29/16 9:52 PM, Steven Schveighoffer wrote:

 import std.experimental.allocator.gc_allocator;

 void main()
 {
     //GCAllocator.instance.goodAllocSize(3000); // error
     writeln(theAllocator.goodAllocSize(3000)); // 3008, should be 4096
 }

 This is known info, why is it not available? Is there a reason this
 needs to be inaccurate? I can create a PR if desired.


 There's no need, I just put in reasonable conservative defaults. Please
 do follow up - thanks! -- Andrei


OK, I'm making a PR for this.

Incidentally, you can do aligned allocation with GC (beyond just 
sizeof(real)). Just make sure your allocation requested is at least that 
many bytes (GC puts data into bins, each bin having the amount of bytes 
requested).

So for example, if you want a 16-byte allocation aligned to 32-bytes, 
just allocate 32 bytes and slice the first 16.

Followup questions:

1. How does one detect that automatic memory cleanup will occur? In 
GCAllocator, deallocate is implemented, so I can't tell that "no you 
don't need to call deallocate"

2. How does one allocate with an allocator for typed info? In other 
words, the GC will call the dtor, but only if it knows what type you put 
in there. With std.experimental.allocator, there isn't a way to do that.

3. I'm working on a library that (hopefully) takes an allocator for 
allocating a ubyte array for buffer space. If I use GCAllocator, this 
will mark the array as having pointers conservatively. It will also 
initialize all the data to 0 (needlessly in this case). How to do this 
correctly?

Thanks

-Steve
Jan 31 2016
next sibling parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 1/31/16 1:52 PM, Steven Schveighoffer wrote:


 OK, I'm making a PR for this.



https://github.com/D-Programming-Language/phobos/pull/3962

-Steve
Jan 31 2016
prev sibling parent reply Jakob Ovrum <jakobovrum gmail.com> writes:
On Sunday, 31 January 2016 at 18:52:48 UTC, Steven Schveighoffer 
wrote:

 2. How does one allocate with an allocator for typed info? In 
 other words, the GC will call the dtor, but only if it knows 
 what type you put in there. With std.experimental.allocator, 
 there isn't a way to do that.


std.allocator.{make, dispose} is the type-aware interface. They 
don't currently do anything with regards to GC, and I don't think 
they really can except for the simplest case where A is exactly 
GCAllocator. If GCAllocator is part of an allocator composition 
or hidden behind IAllocator I don't think `make` can do anything 
about it.

Maybe GCAllocator simply isn't that useful.
Feb 01 2016
parent Jakob Ovrum <jakobovrum gmail.com> writes:
On Tuesday, 2 February 2016 at 05:04:00 UTC, Jakob Ovrum wrote:

 On Sunday, 31 January 2016 at 18:52:48 UTC, Steven 
 Schveighoffer wrote:

 2. How does one allocate with an allocator for typed info? In 
 other words, the GC will call the dtor, but only if it knows 
 what type you put in there. With std.experimental.allocator, 
 there isn't a way to do that.


 std.allocator.{make, dispose} is the type-aware interface. They 
 don't currently do anything with regards to GC, and I don't 
 think they really can except for the simplest case where A is 
 exactly GCAllocator. If GCAllocator is part of an allocator 
 composition or hidden behind IAllocator I don't think `make` 
 can do anything about it.

 Maybe GCAllocator simply isn't that useful.


The issue of scanning is course also an issue when references to 
GC memory are stowed away in non-GC memory allocated with the 
standard allocator interface.
Feb 01 2016