Helen McCall writes:
> My experience is that the performance penalty is not all one suffers
> with automatic garbage collection in POPLOG.
See Steve Knight's contributions on whether there is penalty or gain...
> POPLOG may well collect up garbage and free the memory for it's own
> use, but it does not appear to be very altruistic with respect to
> other processes running on the machine. When making a garbage
> collection, POPLOG actually INCREASES the total amount of memory it is
> using, so forcing other processes running on the machine into an "out
> of swap space" situation and crashing them.
I have never experienced this on any machine I have used Poplog on,
including my laptop... Clearly it is a matter of system configuration, and
I have always used Unix systems configured for people with elephantine
processes (many lisps are far worse). It is true of course that Poplog is
expensive to have around in swap-space as in other things. The non-copying
collector is probably quite a good idea for many purposes.
> Further to this; I have found that POPLOG's own behaviour becomes
> somewhat unpredictable and irrational when swap space runs low, with a
> distinct tendency for conditional branches to default to the else path
> regardless of the evaluation performed, and without signalling any
> error.
This has to be a case of blaming the victim. You don't say which operating
system is involved, but it -must- be the fault of the operating system
if a user process exhibits any behaviour like this in response to a
condition like low swap space.
Certainly I have experienced GC trouble with POPLOG running under A/UX,
which was at the time an apology for a Unix (I don't know what it is like
now). The trouble did clear up when I turned off the copying collector.
But it was quite clear that A/UX was the villain.
> Allowing the programmer to manage the utilisation of resources
> herself, can save an awful lot of heartache!
Well indeed - why don't you throw away the operating system too, and keep
hands on control of all those nice glossy devices?
Robin
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