[Tilesathome] optimizePNGs threading speedup patch

[Rene Wunderlich]

Hi t at h list,

thanks to all t at h members for the big work on osm ;)


and now a bit work from me for u all


WARNIG THIS PATCH IS EXPERIMENTELL!!!!!!!!!!!!!!!!!!!!!!!
do not use it on a unwatched client!


i write a smal patch to add multithreading to the optimizePNGs funktion in 
lib/Compress.pm

threads is a part from perl and not a external thing i hope this sold not a 
prblem say for other systems or archs (not tested)

(fork have to many overhead on 2000 files hehe)


i tested it on a debian sid system with a (AMD Phenom(tm) 9750 Quad-Core Processor).

her my results from

$ time perl tilesGen.pl upload

## patched version ##
## workdir on hardisk
real    3m19.684s
user    7m10.559s
sys     0m35.603s

## workdir on ramdisk
real    1m32.576s
user    5m3.701s
sys     0m21.485s


## svn version ##
## workdir on hardisk
real    12m7.316s
user    10m1.932s
sys     0m24.168s

## workdir on ramdisk
real    9m58.699s
user    9m33.277s
sys     0m20.775s


the map data have i rendered via
perl tilesGen.pl xy some cords of a big city


u can see this give the project many time for real work ;)

i hope i have not make a big error. please test it firt realy hard ;)

please give me feadback and bug reports so i can fix it



René W.

ps: sorry for my bad englich
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