Currently QDoc parses all sources sequentially. This can be improved via (at least partial) parallelization.

There are multiple design choices/patterns that obstruct this so they need to be addressed.

QDoc generates a pre-compiled header (.pch) currently to speed up subsequent processing of C++ source files. This step takes a significant chunk of runtime for an average-sized module and cannot be easily parallelized; Investigate the impact of running QDoc with vs without .pch when parsing is done in parallel.

Address other significant inefficiencies that affect performance.