Add tag for tracking if object is RAII'd or GC'd #25
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ltratt
reviewed
Sep 12, 2024
mark.c
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| GC_ASSERT(n_marks != 0); | ||
| clear_uncollectable_bit_from_hdr(hhdr, bit_no); | ||
| n_marks--; | ||
| hhdr -> hb_n_marks = n_marks; |
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Is there a reason for the "read into n_marks, then decrement it, then write it" dance? If I did something like:
GC_ASSERT(hhdr->hb_n_marks != 0);
clear_uncollectable_...
hhdr->hb_n_marks --;would this still be correct?
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I've looked into this and realised that I'd confused things here. We don't want to adjust the marks at all when hopping between collectable / uncollectable objects. I've pushed a fix here: c65972b
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Please squash. |
To support finalizer elison in Alloy, we need a new way to differentiate between RAII (non-GC'd) and GC'd objects such that this status can be changed dynamically. Currently in BDWGC, if we use GC_malloc and GC_malloc_uncollectable for this distinction, there is no way to change this after an object has been allocated. Using a spare bit in the mark header is a convenient way for us to tell the sweep phase whether or not an object should be considered garbage or whether it is uncollectable while allowing it to be changed in the future.
jacob-hughes
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Squashed |
Merged
via the queue into
softdevteam:master
with commit Sep 16, 2024
a1b1276
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To support finalizer elison in Alloy, we need a new way to differentiate between RAII (non-GC'd) and GC'd objects such that this status can be changed dynamically. Currently in BDWGC, if we use GC_malloc and GC_malloc_uncollectable for this distinction, there is no way to change this after an object has been allocated. Using a spare bit in the mark header is a convenient way for us to tell the sweep phase whether or not an object should be considered garbage or whether it is uncollectable while allowing it to be changed in the future.