In an effort to sustain momentum going into the semester, I was tentatively scheduled to give a talk about KOAP for our research group Tuesday afternoon. KAOP is my tool for developing OpenCL applications using the C host API. I took the opportunity yesterday afternoon to change a few of the things that were bugging me about KOAP.
First, a little bit about how KOAP works internally (well, how it worked until Tuesday). KOAP takes an input file containing C code, OpenCL code, and KOAP directives as input. KOAP expands the directives into OpenCL API calls and combines all of the OpenCL code into a string for compilation at runtime. KOAP does not use formal parsing methods. The parsing takes place over multiple passes and is very ad-hoc. KOAP reads the input into a single string. KOAP processes comments and KOAP includes (like C preprocessor includes) in this first step. KOAP then separates the OpenCL source from the C source and breaks the source strings into double-ended queues (STL deque) of strings, using newline characters as delimiters. KOAP expands directives one line at a time, building a deque of output lines as it goes.
Why STL deques you ask? At one point, that was the only STL container that supported the methods I needed (or thought I needed). My first modification Tuesday was to replace all deques with STL vectors. Vectors support all of the needed operations, and are better suited to the problem (I’m mostly using the element access operator  and the push_back method). KOAP has been released for over two years now, and I’ve spent two years thinking it was dumb that KOAP used double-ended queues. That’s not bugging me anymore.
My other modification is actually user visible. KOAP understands a handful of arguments for things like setting the flags passed to the OpenCL compiler, setting the device type to be used (OpenCL works on CPUs, GPUs, and other accelerators), and a few other things. All of the command line arguments came in pairs (-argname argument). I had written a very dumb bit of code to parse the command line arugments and set the necessary internal flags. My old parser required that the KOAP file for processing be the last argument, and would only process one KOAP file. I’ve rewritten the argument parser to be more general. The new parser is smarter about how it parses the arguments and accepts as many KOAP input files as you wish to give it.
The queues and the argument parser were the two things that bugged me the most about KOAP. Now that they’re fixed, I’m reasonably satisfied with how KOAP is structured internally. I’m not quite to the point of being proud of the codebase, but at least now there’s nothing in KOAP that I find embarrassing.