py/objtype: Implement __del__ data model method for user classes. #18005
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #18005 +/- ##
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Coverage 98.38% 98.39%
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Files 171 171
Lines 22296 22314 +18
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+ Hits 21937 21955 +18
Misses 359 359 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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Code size report: |
Cleans up 2423493, and fixes builds that include LFS but not MICROPY_ENABLE_FINALISER. Signed-off-by: Anson Mansfield <amansfield@mantaro.com>
Signed-off-by: Anson Mansfield <amansfield@mantaro.com>
Signed-off-by: Anson Mansfield <amansfield@mantaro.com>
Signed-off-by: Anson Mansfield <amansfield@mantaro.com>
Signed-off-by: Anson Mansfield <amansfield@mantaro.com>
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Remaining TODO:
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Other than for freeing resources obtained through FFI, what use case would it have in MicroPython? |
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Summary
This PR implements the required functionality to allow the garbage collector to run user-defined
__del__methods as finalisers.Testing
I've added full-coverage tests of this feature that I've tested for sensitivity across both the Unix port and my RP2040 and RP2350 boards. All tests pass on my RP2 boards, and with one very difficult exception noted below all tests also pass on unix.
tests/basics/class_del_postadded.pyonly passes on the unix builds I've built withDEBUG=1; but fails on myDEBUG=0builds. I suspect that this is an underlying garbage-collector bug, rather than a bug with this implementation of__del__specifically. So far I've failed to discover exactly why it is this occurs, though I've confirmed using the debugger on a non-debug non-stripped build that everything up to and including the call tomp_obj_malloc_var_with_finaliserdoes run as expected.Trade-offs and Alternatives
This PR claims two additional bits from the
mp_obj_type_t.flagsfield, forMP_TYPE_FLAG_IS_INSTANCEDandMP_TYPE_FLAG_HAS_FINALISER. The latter bit is required in order to track whether instances should be allocated using the_with_finaliserallocators, while the former is required to track whether or it's safe to allow the__del__method to be inserted into a class after-the-fact. It's possible thatMP_TYPE_FLAG_IS_INSTANCEDcould be eliminated by forbidding this type of insertion entirely.Alternatively, almost all of the code complexity in this PR could be eliminated by unconditionally allocating objects from user-defined classes with
mp_obj_malloc_var_with_finaliser; however the performance penalty that this would introduce on classes that don't use it leads me to favor this more-complex approach.