Race condition generating PIO headers

[Gadgetoid]

When building MicroPython from source including our C++ modules that include PIO headers, and typically with -j2 (or more) to parallelize the build tasks, it seems files depending on PIO headers are compiled before pioasm has even finished building 😬

It seems like a race condition relating to pico_generate_pio_header but I have yet to encounter it on non-MicroPython builds, so there might be something unique about our setup that's causing issues. EG:

[ 30%] Building CXX object CMakeFiles/pioasm.dir/pio_disassembler.cpp.o
[ 40%] Building CXX object CMakeFiles/pioasm.dir/gen/lexer.cpp.o
[ 50%] Building CXX object CMakeFiles/pioasm.dir/gen/parser.cpp.o
[ 60%] Building CXX object CMakeFiles/pioasm.dir/c_sdk_output.cpp.o
[ 70%] Building CXX object CMakeFiles/pioasm.dir/python_output.cpp.o
[ 80%] Building CXX object CMakeFiles/pioasm.dir/hex_output.cpp.o
[ 90%] Building CXX object CMakeFiles/pioasm.dir/ada_output.cpp.o
In file included from /home/runner/work/pimoroni-pico/pimoroni-pico/pimoroni-pico-f0975778f6a614886aa516a7d513625bfc194598/micropython/modules/picographics/picographics.cpp:1:
/home/runner/work/pimoroni-pico/pimoroni-pico/pimoroni-pico-f0975778f6a614886aa516a7d513625bfc194598/micropython/modules/../../drivers/st7789/st7789.hpp:14:10: fatal error: st7789_parallel.pio.h: No such file or directory
   14 | #include "st7789_parallel.pio.h"
      |          ^~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
In file included from /home/runner/work/pimoroni-pico/pimoroni-pico/pimoroni-pico-f0975778f6a614886aa516a7d513625bfc194598/micropython/modules/picographics/../../../drivers/st7789/st7789.cpp:1:
/home/runner/work/pimoroni-pico/pimoroni-pico/pimoroni-pico-f0975778f6a614886aa516a7d513625bfc194598/micropython/modules/picographics/../../../drivers/st7789/st7789.hpp:14:10: fatal error: st7789_parallel.pio.h: No such file or directory
   14 | #include "st7789_parallel.pio.h"
      |          ^~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
[100%] Linking CXX executable pioasm
[100%] Built target pioasm
[  4%] No install step for 'PioasmBuild'
[  4%] Completed 'PioasmBuild'
[  4%] Built target PioasmBuild
[  4%] Generating bs2_default.bin
[  4%] Generating bs2_default_padded_checksummed.S
[  4%] Built target bs2_default_padded_checksummed_asm
[  4%] Generating cyw43_bus_pio_spi.pio.h
[  4%] Built target cyw43_driver_picow_cyw43_bus_pio_spi_pio_h
[  4%] Generating st7789_parallel.pio.h
[  4%] Built target usermod_picographics_st7789_parallel_pio_h
[  4%] Generating apa102.pio.h
[  4%] Built target usermod_plasma_apa102_pio_h
[  4%] Generating ws2812.pio.h
[  4%] Built target usermod_plasma_ws2812_pio_h
[  5%] Generating pwm_cluster.pio.h
[  5%] Built target usermod_pwm_pwm_cluster_pio_h
[  5%] Generating encoder.pio.h
[  5%] Built target usermod_encoder_encoder_pio_h