D2 weak references

[Jason House]

grauzone Wrote:

> > Is it possible for druntime to expose an option as to whether or not the 
> > sweep phase / finalizers should run while all threads are suspended?
> 
> But then you can only do boring stuff in the finalizer. Calling any C or 
> library function must be avoided, because it can lead to deadlocks. At 
> the same time, your code is called at arbitrary times, and anything you 
> do will cause race conditions by default. It's like a UNIX signal 
> handler: programming in it sucks so much.

I've never had this kind of issue with finalizers, so I have limited appreciation for the argument. In the application I'm working on, I have no need for any functionality in this area except weak reference support.
 
> Maybe the finalizer register function could take two callbacks: one 
> called before threads are resumed, and one after threads are resumed. 
> You could use the first callback to zero out the weak reference, while 
> the second takes care of advanced functionality, like notifying someone 
> that the reference has been collected.

Wouldn't that implicitly require two sweep phases? In my last post, I suggested the possibiluty of a callback in the mark phase. At the moment, I'm thinking one callback at the start of collection and another callback when marking a weakly referenced object would do the trick. Any weakly referenced object not marked after the last collection is invalid