Add option for strict write barriers #1008
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joncham
reviewed
Aug 9, 2018
| @@ -198,13 +198,15 @@ create_domain_objects (MonoDomain *domain) | |||
| mono_error_assert_ok (&error); | |||
| mono_field_static_set_value (string_vt, string_empty_fld, empty_str); | |||
| domain->empty_string = empty_str; | |||
| mono_gc_wbarrier_generic_nostore (&domain->empty_string); | |||
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Not sure it matters, but would replacing assignment above with mono_gc_wbarrier_generic_store be better?
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yeah, guess that is nicer. Will change and then merge.
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It may make merge conflicts with upstream more frequent. Just wondering what practical difference is if anything.
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there should be no practical difference
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Looking at it, I decided not to change it. The functionality is identical, and the code did not look nicer by merging the assignment and the write barrier, as lines become very long. Merged as is.
joncham
approved these changes
Aug 9, 2018
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#958 added support for incremental Boehm GC by adding write barriers to mono.
Incremental Boehm requires only one write barrier call on any pointer within an object even if multiple references in the object have changed, as the object is then considered as dirty, and rescanned.
However, our technique for validating correct use of write barriers (by verifying that all found references have been set through a write barrier call) is not that tolerant (And potentially, neither are future Boehm replacements). So, to get a good test coverage for write barrier use to work, we need an option to set write barriers on all reference writes. Mono has some functions which touch whole blocks of managed memory (which may contain references). This PR adds a "strict write barrier" mode, which will set write barriers for each potential reference in those functions.
This needs to land in order to get test coverage on write barrier use in Unity to run.