[Tuxmath-devel] Further performance improvement with more caching mechanisms

[Wenyuan G. <guo...@gm...>]

Hi all,

With more careful profiling of the program, I found my earlier theory
to be wrong: I thought the delay when switching resolution mainly came
from HDD delay. This component turns out to be minor, thanks to OS
caching. The following two components are much more significant:

1. Surprisingly, the librsvg function that determines the dimension of
an input SVG image file takes substantial time. I had thought that it
ought to be as simple as to locate the relevant strings from the SVG
file involving only minimum parsing efforts. In any case, I have build
an in-memory caching table to store dimensions of SVG files seen
before to minimize this performance penalty to once per file for each
session.

2. The PNG function to parse input file into SDL surface is the second
contributor to the delay, although smaller than 1. I have built
another in-memory caching mechanism for these SDL surfaces, with
reference copying instead of actual data copying. This assumes that
all loaded SDL surfaces are never modified, which seem to be the case
for tuxmath. This is faster and more memory efficient.

With the additional caching, pressing F10 to switch resolution takes
only 0.5s, compared with about 2s before. Given this small delay, I
have scratched the multithreading mechanism implemented before, which
is no longer necessary. Moreover, the multithreading functions still
have mysterious bugs. There are too many rendering functions that have
global variable and I/O conflicts. It is extremely difficult to
identify all race conditions between them at this point.

Cheers
Wenyuan