Libstdc++-v3 use to provide a locked implementation of classes for sizes
which didn't have lock-free support. That was removed for this release
as it caused a program compiled with a specific version of GCC to be
locked into that implementation. The design criteria for the new
__atomic builtins required that when the compiler cannot provide a lock
free routine for some object, a call to an external library would be
made. This allows legacy code to be "upgraded" at a later date by
providing a new library with improved support. It will also facilitate
a standard library to be used for C1x as well without requiring C++.
The desire is that this library *not* be an integral part of the
compiler, but be provided by the OS or some application layer. Until
this has been around a while and the library standardized/accepted there
isn't going to be such a generally available library. Until one is
available, there should be something which is easily accessible which
can be built as required.
I've made a rough initial implementation of libatomic which can built
and linked in to a program which satisfies all the ABI requirements of
http://gcc.gnu.org/wiki/Atomic/GCCMM/LIbrary
My question is, what do I do with it :-P The thoughts that first come
to mind are:
- It could be added into the gcc build tree, and optionally configured
and built so that if anyone needs it, its there.
- It could be a separate project hosted outside the gcc source tree.
Where would the best place be?
- simply make it a part of libgcc for now and worry about separating it
later.
- It could just be a source file available for download from the GCC
wiki, or elsewhere.
I imagine there are other options too...
Thoughts?
Andrew
PS. Reflecting upon it, I wonder if it could be a part of the gcc
libraries like libgomp or libitm are. During configuration we could
check to see if there is an existing libatomic in the system, and if
there is NOT, enable building libatomic... Maybe that would be
best? then it would "just work" for all gcc users. Or at least the
vast majority.
A bit late in the game for this release, so an easily downloadable
source file would probably have to do this time around for anyone that
happens to need it for non-lockfree atomics...
