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digitalmars.D.learn - A question about the GC

reply Jarrod <qwerty ytre.wq> writes:
Hey all,

I have a C library that takes the address to a class and stores it, 
associating the address of the class with a cluster of data. That way, if 
I try to create a second class tied to the same data, it merely passes 
back the address of the first class. Also, if the data is destroyed, it 
explicitly calls the class destructor for me.

This is all well and good, but my concern is that the garbage collector 
may reallocate my class if it is a 'copying' gc (I'm not really sure what 
it really is, I can't see it mentioned anywhere). If my class is moved, 
what happens to the pointers in my C code? Will they be updated too? I 
doubt it.
Is this a cause for concern or is D's GC of the non-moving variety? If it 
does indeed move I guess I'll have to override new/delete.

Thanks,
Dec 23 2007
next sibling parent reply Kirk McDonald <kirklin.mcdonald gmail.com> writes:
Jarrod wrote:

 Hey all,
 
 I have a C library that takes the address to a class and stores it, 
 associating the address of the class with a cluster of data. That way, if 
 I try to create a second class tied to the same data, it merely passes 
 back the address of the first class. Also, if the data is destroyed, it 
 explicitly calls the class destructor for me.
 
 This is all well and good, but my concern is that the garbage collector 
 may reallocate my class if it is a 'copying' gc (I'm not really sure what 
 it really is, I can't see it mentioned anywhere). If my class is moved, 
 what happens to the pointers in my C code? Will they be updated too? I 
 doubt it.
 Is this a cause for concern or is D's GC of the non-moving variety? If it 
 does indeed move I guess I'll have to override new/delete.
 
 Thanks,


It is a non-moving GC. Also, the D GC won't see any pointers held by the 
C library, so be sure that you keep references to your GC-controlled 
classes in your D code, where the GC can see them.

-- 
Kirk McDonald
http://kirkmcdonald.blogspot.com
Pyd: Connecting D and Python
http://pyd.dsource.org
Dec 23 2007
parent reply Jarrod <qwerty ytre.wq> writes:
On Sun, 23 Dec 2007 20:27:59 -0800, Kirk McDonald wrote:
 

 It is a non-moving GC. Also, the D GC won't see any pointers held by the
 C library, so be sure that you keep references to your GC-controlled
 classes in your D code, where the GC can see them.


Yes, I use gc.addRoot with the class address before I pass it on..

Anyway, thanks a lot for your quick answer! I hope the GC remains non-
moving, it becomes a lot more confusing otherwise.
Dec 23 2007
parent 0ffh <frank frankhirsch.youknow.what.todo.net> writes:
Jarrod wrote:

 Anyway, thanks a lot for your quick answer! I hope the GC remains non-
 moving, it becomes a lot more confusing otherwise.


IIRMHOC, you have little to fear (at least for D1), because a moving
collector is not possible unless some other features are removed from
the language first (e.g. unions and void* types).

regards, frank
Dec 24 2007
prev sibling parent "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"Jarrod" <qwerty ytre.wq> wrote in message 
news:fkn8sd$sl0$1 digitalmars.com...


 This is all well and good, but my concern is that the garbage collector
 may reallocate my class if it is a 'copying' gc (I'm not really sure what
 it really is, I can't see it mentioned anywhere). If my class is moved,
 what happens to the pointers in my C code? Will they be updated too? I
 doubt it.


As Kirk pointed out, D's current collector is a non-moving collector, but in 
the event that a moving collector is implemented, most moving collectors 
provide a method to "pin" a piece of memory to disallow it from being moved.
Dec 23 2007