How to perform atomic operations on Linux?

Question

Every Modern OS provides today some atomic operations:

• Windows has Interlocked* API
• FreeBSD has <machine/atomic.h>
• Solaris has <atomic.h>
• Mac OS X has <libkern/OSAtomic.h>

Anything like that for Linux?

• I need it to work on most Linux supported platforms including: x86, x86_64 and arm.
• I need it to work on at least GCC and Intel Compiler.
• I need not to use 3rd par library like glib or qt.
• I need it to work in C++ (C not required)

Issues:

• GCC atomic builtins __sync_* are not supported on all platforms (ARM) and are not supported by the Intel compiler.
• AFAIK <asm/atomic.h> should not be used in user space and I haven't successfully used it at all. Also, I'm not sure if it would work with Intel compiler.

Any suggestions?

I know that there are many related questions but some of them point to __sync* which is not feasible for me (ARM) and some point to asm/atomic.h.

Maybe there is an inline assembly library that does this for GCC (ICC supports gcc assembly)?

Edit:

Very partial solution for add operations only (allows implementing atomic counter but not lock free-structures that require CAS):

If you use libstc++ (Intel Compiler uses libstdc++) then you can use __gnu_cxx::__exchange_and_add that defined in <ext/atomicity.h> or <bits/atomicity.h>. Depends on compiler version.

Answer 1

Darn. I was going to suggest the GCC primitives, then you said they were off limits. :-)

In that case, I would do an #ifdef for each architecture/compiler combination you care about and code up the inline asm. And maybe check for __GNUC__ or some similar macro and use the GCC primitives if they are available, because it feels so much more right to use those. :-)

You are going to have a lot of duplication and it might be difficult to verify correctness, but this seems to be the way a lot of projects do this, and I've had good results with it.

Some gotchas that have bit me in the past: when using GCC, don't forget "asm volatile" and clobbers for "memory" and "cc", etc.

Answer 2

Boost, which has a non intrusive license, and other frameworks already offer portable atomic counters -- as long as they are supported on the target platform.

Third party libraries are good for us. And if for strange reasons your company forbid you from using them, you can still have a look at how they proceed (as long as the licence permit it for your use) to implement what your are looking for.