esp32/main: Store native code as linked list instead of list on GC heap. #15589
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projectgus
approved these changes
Aug 6, 2024
Finalisers that run during `gc_sweep_all()` may run native code, for example if an open file is closed and the underlying block device is implemented in native code, then the filesystem driver (eg FAT) may call into the native code. Therefore, native code must be freed after the call to `gc_sweep_all()`. That can only be achieved if the GC heap is not used to store the list of allocated native code blocks. Instead, this commit makes the native code blocks a linked list. Signed-off-by: Damien George <damien@micropython.org>
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Summary
Finalisers that run during
gc_sweep_all()may run native code, for example if an open file is closed and the underlying block device is implemented in native code, then the filesystem driver (eg FAT) may call into the native code.Therefore, native code must be freed after the call to
gc_sweep_all(). That can only be achieved if the GC heap is not used to store the list of allocated native code blocks. Instead, this commit makes the native code blocks a linked list.Testing
Tested on an ESP32C3, running the native tests as per #15551:
All the tests pass.
Note: requires #15573, #15575.
Trade-offs and Alternatives
This approach uses 4 bytes extra iRAM per native function, but keeps the code simple and understandable. An alternative would be to still use the GC heap to store the list of native memory blocks, and make
gc_sweep_all()only call the finalisers, not actually reclaim/clear memory. That's a complex change to make though.