[meow_cat]

During my masters thesis in a chemistry lab, I got a side task to look at a data analysis script and make it run faster. It was a "C/C++" code (i.e. procedural C-style code using C++ stdlib for convenience) that read a file line by line and then fed it to a slow processing function, then aggregated the results. It took over a day to run.

Without even looking at the processing function, which I considered some sciency science, I set up pthreads and mutexes on the result array and such to reap almost perfectly linear scaling. So far, so good.

Then I ran a profiler to see what was actually taking so long.

... Uh, why are you spending all this time copying strings back and forth?

Turns out they passed all strings by value. Sprinkling in a few const & here and there got a 1000-fold speedup or such. I felt pretty stupid for my multithreading antics after that.