[Lldb-commits] [PATCH] D48393: Make DWARFParsing more thread-safe

[Pavel Labath via Phabricator via lldb-commits]

labath added a comment.

I am not sure this will actually solve the problems you are seeing. This may avoid corrupting the internal DenseMap data structures, but it will not make the algorithm using them actually correct.
For example the pattern in `ParseTypeFromDWARF` is:

1. check the "already parsed map". If the DIE is already parsed then you're done.
2. if the map contains the magic "DIE_IS_BEING_PARSED" key, abort (recursive dwarf references)
3. otherwise, insert the  "DIE_IS_BEING_PARSED" key into the map
4. do the parsing, which potentially involves recursive `ParseTypeFromDWARF` calls
5. insert the parsed type into the map

What you do is make each of the steps (1), (3), (5) atomic individually. However, the whole algorithm is not correct unless the whole sequence is atomic as a whole. Otherwise, if you have two threads trying to parse the same DIE (directly or indirectly), one of them could see the intermediate DIE_IS_BEING_PARSED and incorrectly assume that it encountered recursive types.

So, I think that locking at a higher level would be better. Doing that will certainly be tricky though...


https://reviews.llvm.org/D48393