[gclist] User Visible GC

[Nick Kramer]

I've recently encountered several issues which involve a GC-like idea, but
which is visible to the user.  For instance, one example would be a pop-up
dialog when the user goes to save a compound document -- "This component is
no longer referenced from any document.  Would you like me to save it
anyway?"  I ended up writing what was essentially a trivial mark-and-sweep
GC to implement this.

A somewhat different example would be Emacs' undo list.  It keeps undo
information for at least the last N commands, but depending on when the
last garbage collection ran, it sometimes keeps more.

Both of these do something similar to garbage collection, but they do it on
user visible objects.  What's the best way to program these sorts of features?


-Nick Kramer