Portable Compare And Swap (atomic operations) C/C++ library?

Question

OPA (Open Portable Atomics) could be a good fit for your needs. https://trac.mcs.anl.gov/projects/openpa/

It provides a consistent C API to common atomic operations across multiple platforms under an MIT-style license. The library is small and certainly meets your size requirements. The current platform list is:

• GCC inline assembly for x86, x86_64, ia64, PPC 440, and MIPS 5K processors. Several compilers with GCC-compatible-ish front-ends are also supported on the same architectures, such as icc, PGI, and IBM's xlc.
• GCC atomic intrinsics, so most GCC-4.1+ installations are supported.
• The SUN Solaris atomic operations library.
• Windows NT intrinsics (although you currently have to do a little bit of extra work to build on Windows).
• Two pseudo-platforms, pthread mutex based emulation for portability to otherwise unsupported platforms (while sacrificing some performance), and an "unsafe" implementation for use in code that is conditionally compiled to be single-threaded code.

I've never used it in a C++ program, although it ought to work with little or no changes. I'd be happy to tweak it if you run into trouble (just mail [email protected]).

The boost interprocess library might be what you are after -- the Atomic.hpp include file contains compare-and-swap implementations for a variety of platforms and compilers.

Intel Threading Building Blocks has a nice portable atomic<T> template which does what you want. But whether it is a small library or not can of course be debated..

You might be interested in Glib's Atomic Operations functions,

g_atomic_int_compare_and_exchange()

implements the CAS semantics for various architectures. The implementation itself is relatively easy to understand and can be used stand-alone without too much effort, you can find it at svn.gnome.org/viewvc/ under glib/trunk/glib/gatomic.{c,h}. Hope this helps!