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6 hours ago
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Writing your own standard library is all fun and games until someone (which is to say yourself) asks the important question: could this be actually used for real? Theories and opinions can be thrown about the issue pretty much forever, but the only way to actually know for sure is to do it.
Thus I converted CapyPDF, which is a fairly compact 15k LoC codebase from the C++ standard library to Pystd, which is about 4k lines. All functionality is still the same, which is to say that the test suite passes, there are most likely new bugs that the tests do not catch. For those wanting to replicate the results themselves, clone the CapyPDF repo, switch to the pystdport branch and start building. Meson will automatically download and set up Pystd as a subproject. The code is fairly bleeding edge and only works on Linux with GCC 15.1.
One of the original reasons for starting Pystd was being annoyed at STL compile times. Let's see if we succeeded in improving on them. Build times when using only one core in debug look like this.
When optimizations are enabled the results look like this:
In both cases the Pystd version compiles in about a quarter of the time.
C++ gets a lot of valid criticism for creating bloated code. How much of that is due to the language as opposed to the library?
That's quite unexpected. The debug info for STL types seems to take an extra 20 megabytes. But how about the executable code itself?
STL is still 200 kB bigger. Based on observations most of this seems to come from stdlibc++'s implementation of variant. Note that if you try this yourself the Pystd version is probably 100 kB bigger, because by default the build setup links against libsubc++, which adds 100+ kB to binary sizes whereas linking against the main C++ runtime library does not.
Ok, fine, so we can implement basic code to build faster and take less space. Fine. But what about performance? That is the main thing that matters after all, right? CapyPDF ships with a simple benchmark program. Let's look at its memory usage first.
Apologies for the Y-axis does not starting at zero. I tried my best to make it happen, but LibreOffice Calc said no. In any case the outcome itself is expected. Pystd has not seen any performance optimization work so it requiring 10% more memory is tolerable. But what about the actual runtime itself?
This is unexpected to say the least. A reasonable result would have been to be only 2x slower than the standard library, but the code ended up being almost 25% faster. This is even stranger considering that Pystd's containers do bounds checks on all accesses, the UTF-8 parsing code sometimes validates its input twice, the hashing algorithm is a simple multiply-and-xor and so on. Pystd should be slower, and yet, in this case at least, it is not.
I have no explanation for this. It is expected that Pystd will start performing (much) worse as the data set size grows but that has not been tested.
