Both are atomic, but the cmpxchg has memory ordering hints. We
give this acquire semantics.
NOTE: The unlock in libc_r is implemented by a "normal" assign
statement. This is not correct on ia64 due to the memory ordering
characteristics of the architecture. We need release semantics
for an unlock.
completeness and doesn't get us a working libc_r there because libc_r
uses setjmp() and setjmp() cannot be used for context switches on ia64
as-is (or sparc64). Rather than making setjmp/longjmp behave like
the *context() calls, it would be far better to make libc_r use *context()
directly which is what they are for.
Obtained from: marcel
