• Mike Hearn <mike plan99.net> Nov 18 2009
• Walter Bright <newshound1 digitalmars.com> Nov 18 2009

Mike Hearn <mike plan99.net> writes:

 Mixing D's gc world with manually managed memory isn't 
 hard, as long as  the following rules are followed:
 
 1. don't allocate in one language and expect to free in another
 2. keep a 'root' to all gc allocated data in the D side of the fence 
 (otherwise it may get collected)


Yes it's the second that's the tough part. For instance consider the case of
passing a callback (delegate) to the RPC system written in c++. How do you keep
the associated data rooted without causing leaks? You'd need to remember to
manually add it to the gc roots when the callback object is created and then
unroot them when it's invoked. So this needs some kind of glue/binding system.

I'm not saying it's impossible or even hard. Just that I've seen such things
done before and they were non-trivial.

Walter Bright <newshound1 digitalmars.com> writes:

Mike Hearn wrote:
 Mixing D's gc world with manually managed memory isn't hard, as
 long as  the following rules are followed:
 
 1. don't allocate in one language and expect to free in another 2.
 keep a 'root' to all gc allocated data in the D side of the fence 
 (otherwise it may get collected)


 Yes it's the second that's the tough part. For instance consider the
 case of passing a callback (delegate) to the RPC system written in
 c++. How do you keep the associated data rooted without causing
 leaks? You'd need to remember to manually add it to the gc roots when
 the callback object is created and then unroot them when it's
 invoked. So this needs some kind of glue/binding system.
 
 I'm not saying it's impossible or even hard. Just that I've seen such
 things done before and they were non-trivial.


Most of the time, nothing needs to be done because the reference is on 
the parameter stack that calls the C function.

For the callback object, manually adding/removing the root (there are 
calls to the gc to do this) shouldn't be any more onerous than manually 
managing memory for it, which is done in C/C++ anyway.