[PATCH] D28220: provide Win32 native threading

[David Majnemer via Phabricator via cfe-commits]

majnemer added inline comments.


================
Comment at: include/__threading_support:300-305
+int __libcpp_recursive_mutex_init(__libcpp_mutex_t *__m)
+{
+  InitializeSRWLock(__m);
+  return 0;
+}
+
----------------
compnerd wrote:
> majnemer wrote:
> > I don't think you can use slim rw locks for recursive locks. I think we will need to use `CRITICAL_SECTION` for those. std::recursive_mutex can't be used with std::condition_variable AFAIK so all you need (I think) is recursive versions of `__libcpp_mutex_...`
> > 
> > Recursive locks should be used far less frequently which makes it valuable, IMO, to use slim rw locks for the non-recursive mutex implementation.
> You are absolutely right.  That was something that I looked at originally and went with the CS.  However, the overhead of a tagged struct is 5 or 9 bytes (sizeof(void *) + 1) bytes (ignoring padding for MS ABI).  Going with that should give the benefits of always being able to properly initialize the CS instead of the kludge.
Er, isn't the overhead much more than that? IIRC, `CRITICAL_SECTION` is quite large. You'd be making all the users of `std::mutex` pay for the space of `std::recursive_mutex`...


Repository:
  rL LLVM

https://reviews.llvm.org/D28220