On Wednesday, 24 October 2012 at 18:26:48 UTC, Rob T wrote:
On Wednesday, 24 October 2012 at 12:21:03 UTC, Paulo Pinto
wrote:
Having dealt with systems programming in languages with GC
(Native Oberon, Modula-3), I wonder how much an optional GC
would really matter, if D's GC had better performance.
--
Paulo
Well, performnce is only part of the GC equation. There's
determinism, knowing when the GC is invoked and ability to
control it, and increased complexity introduced by a GC, which
tends to increase considerably when improving the GCs
performance and ability to manage it manually. All this means
there's a lot more potential for things going wrong, and this
cycle of fixing the fix may never end.
The cost of clinging onto a GC may be too high to be worth
relying on as heavily as is being done, and effectivly forcing
a GC on programmers is the wrong approach because not everyone
has the same requirements that require its use. When I say
"forcing", look at what had to be done to fix the performance
of the game in question, what was done to get rid of the GC was
a super-human effort and that is simply not a practical
solution by any stretch of the imagination.
A GC is both good and bad, not good for everyone and not bad
for everyone, with shades of gray in between, so it has to be
made fully optional, with good manual control, and easily so.
--rt
I do understand that.
But on the other hand there are operating systems fully developed
in such languages, like Blue Bottle,
http://www.ocp.inf.ethz.ch/wiki/Documentation/WindowManager
Or the real time system developed at ETHZ to control robot
helicopters,
http://static.usenix.org/events/vee05/full_papers/p35-kirsch.pdf
I surely treble at the thought of a full GC collection in plane
software. On the other hand I am old enough to remember the
complaints that C was too slow and one needed to write everything
in Assembly to have full control of the application code.
Followed by C++ was too slow and one should use C structs with
embedded pointers to have full control over the memory layout of
the object table, instead of strange compiler generated VMT
tables.
So I always take the assertions that manual memory management is
a must with a grain of salt.
--
Paulo
