[PATCH] D28220: provide Win32 native threading

[Shoaib Meenai via Phabricator via cfe-commits]

smeenai added inline comments.


================
Comment at: include/__threading_support:300-305
+int __libcpp_recursive_mutex_init(__libcpp_mutex_t *__m)
+{
+  InitializeSRWLock(__m);
+  return 0;
+}
+
----------------
majnemer wrote:
> 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`...
Yeah, CRITICAL_SECTION is 24 bytes vs 4 bytes for a SRWLOCK.


Repository:
  rL LLVM

https://reviews.llvm.org/D28220