[PATCH] D37677: [libc++] implement future synchronization using atomic_flag

[Eric Fiselier via Phabricator via cfe-commits]

EricWF requested changes to this revision.
EricWF added a comment.
This revision now requires changes to proceed.

I agree with the general consensus that we should only make this change if it's significantly faster, and only after we have a test that demonstrates this.

Unfortunately I don't recall exactly why I wrote that TODO in the first place, but I'm sure I meant changing `__state_`, and not the lock. I suspect it had to do with http://llvm.org/PR24692 .



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Comment at: include/future:538
+
+    mutable class __spin_lock
+    {
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It seems this change is ABI breaking, since `mutex` and `__spin_lock` don't have the same layout. The change will need to be guarded behind a `_LIBCPP_ABI_FOO` macro. See `__config` for examples.


https://reviews.llvm.org/D37677