Lazy copies of domains

[xbrukner]

It is usual, that when copy of some object is created, the copy might not be modified during its lifetime. In that case it would be great if the copy of object was only created if needed, otherwise call method of original instance (or return an attribute).

[karelklic]

The Qt library uses copy-on-write for their classes. It's described in http://doc.qt.digia.com/qt/implicit-sharing.html.

Here is their copy-on-write pointer: http://doc.qt.digia.com/qt/qshareddatapointer.html

[karelklic]

Current performance of master branch (no copy on write), super_ptr branch (cow limited to some domains?), and shared_data_pointer branch:

/usr/bin/time -v tool/canal tests/wc.s -e run -e quit

master
        User time (seconds): 88.92
        System time (seconds): 1.33
        Elapsed (wall clock) time (h:mm:ss or m:ss): 1:30.38
        Maximum resident set size: 1 287 MB
super_ptr
        User time (seconds): 32.50
        System time (seconds): 0.13
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:32.70
        Maximum resident set size (kbytes): 60,3 MB
shared_data_pointer
        User time (seconds): 30.01
        System time (seconds): 0.03
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:30.06
        Maximum resident set size (kbytes): 31,1 MB

[karelklic]

Hehe, optimization on domain comparison operators, shared_data_pointer branch:

Before:

/usr/bin/time -v tool/canal tests/wc.s -e run -e quit
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:30.06

After:

/usr/bin/time -v tool/canal tests/wc.s -e run -e quit
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.82

[xbrukner]

Oh crap, mine is slower :D 5.76s and 60MB on wc.

[sutamatej]

:thumbsup:

[karelklic]

Fixed in e7adf61f45ff0d2d47532e1e0b1013df151e6aa4.