[D-runtime] Precise garbage collection

[Michel Fortin]

Le 8-août-2013 à 0:54, Rainer Schuetze <r.sagitario at gmx.de> a écrit :

> On 08.08.2013 03:05, Michel Fortin wrote:
>> Funny problem. But there's no ambiguity really because you can't
>> create using "new" a memory block that'll only contain a reference to
>> an object. You can thus be sure that if the root type of a memory
>> block is a TypeInfo_Class it truly is an object of that class; and if
>> a*variable*  has TypeInfo_Class then it's a reference.
> 
> That's what my code currently assumes. But that doesn't work if std.emplace is used to create a class instance into the memory of a struct instance. How can you distinguish that the memory is used as a reference or an instance of that class.

More importantly, how would emplace signal the GC that it is instantiating an object of a certain type in "void[]" memory in the first place? For all you know, with emplace one could construct and destruct and reconstruct objects of different classes, or things other than classes, in the same block of memory. If emplace is calling a specific function to add a root of a certain type, you can create a special flag or separate function for "in-place objects" and make emplace call this function.

> The same happens with classes generated into the data segment by the compiler, e.g. TypeInfo_Class objects. These currently don't have mutable references that could point into GC allocated memory, but a recent change also allows creating user defined class instances to be built into the data segment.

I can't really comment on this because I have no idea how you're getting any typeinfo for the data segment.

-- 
Michel Fortin
michel.fortin at michelf.ca
http://michelf.ca