[gclist] Destructor functions and GC

[Dave Lloyd]

Some of the revent posts on GC and OO have reminded me of a problem that 
occurred to me some years ago: how does a GC interact with destructor 
functions? Algol 68 doesn't provide these, but I have often felt a twinge of 
need for them (and then promptly done the same manually). A good example from 
recent events is the use of system-supplied semaphores which must be returned 
(closed) when finished with.  However with the normal free scheme, you know 
exactly when these functions will get called, what is in scope, the state of 
any external IO, etc - and most uses I think of for destructor functions are 
definitely NOT context-free.

With the sort of heap I run, it is not even easy to spot objects that are no 
longer accessible (I only see words that are inaccessible). I doubt this need
be a problem if the original allocation blocks are tagged someway. But the 
question is, what do you do about the context in which destructor functions are
called?

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Dave Lloyd                            Email: Dave@occl-cam.demon.co.uk
Oxford and Cambridge Compilers Ltd    Phone: (44) 1223 572074
55 Brampton Rd, Cambridge CB1 3HJ, UK