[PATCH] D54995: [MemoryBuffer] By default assume that all files are volatile to prevent unintended file locks

[Ilya Biryukov via Phabricator via cfe-commits]

ilya-biryukov added a subscriber: zturner.
ilya-biryukov added a comment.

cross-posting @zturner's comment from the mailing thread for the record:

> I’m afraid this is going to be too severe a performance regression if we change the default. So I don’t think this should be an LLVM-wide default

And yet, before proceeding further with this, could we figure out the exact cause of the issue? I.e.

- What are the combination of file open flags that force the files to be locked on windows?
- Is there a way to memory map a file on Windows without locking a file?
- What is the sequence of actions that trigger this in clang? Is it hard to notice because we keep files mmapped for small periods of time?
- Can we try to make a reliable repro? Even if it's infrequent, there are probably various hacky ways to make it more reproducible, e.g. adding sleeps into various points to keep the files locked for longer.




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https://reviews.llvm.org/D54995