22.09.2014 0:28, Peter Popov:
[...]
So, for classes which are reference counted, store the reference count @
the highest two bytes of the class instance (which in practice is a
pointer to the VMT). This would let you ref-count up to 2^16. You need to
mask it out from the rest of the pointer when accessing VMT. No need for
additional changes to the RTTI, just mask the highest two bytes when using
the class.
This would look aesthetically horid at least. Somehow reminds of
segment:offset ugliness of 8086 ;-)
Besides, thinking about a magnificent brand new pointer type, and as
long as certain performance penalties can be tolerated, one might want
to also consider providing some path for heap defragmentation, for the
sake of completeness (Not that I know how to properly do it, but still
my $0.02).
Regards,
Nikolai
Peter
On Sun, 21 Sep 2014 23:03:43 +0300, Boian Mitov <mi...@mitov.com> wrote:
This is not true. Ref pointer is exactly the same size as non ref
pointer. the counter is in the instance not in the pointer to the
instance ;-) .
You can study the interface implementations or the String
implementations they are done the same way.
With best regards,
Boian Mitov
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Mitov Software
www.mitov.com
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-----Original Message----- From: Peter Popov
Sent: Sunday, September 21, 2014 12:29 PM
To: fpc-devel@lists.freepascal.org ; Sven Barth
Subject: Re: [fpc-devel] Suggestion: reference counted objects
Sven,
based on your comments a bizarre thought came to me. Currently, class
instances are pointers. What you propose will somehow create a special
pointer type (referenced class).
Should this be done, I have a request: create a 4 byte "compressed" class
reference which expands into an 8 byte pointer type prior to usage:
1. Most architectures align data.
2. 64 bit comps align pointers on 8 byte boundaries, meaning that the 3
leftmost bits are 0.
3. You could store a class pointer as a 4 byte integer and, prior to
usage, expand it to 8 bytes a leftshift 3.
In this way you will have 64GB of data available to your program and your
pointers will occupy twice less. If, for example one uses large amount of
pointers, this could be ... aesthetically pleasing ...
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