Jonas Maebe wrote:
If you'd want to limit the length to 2GB on 64 bit systems. I also don't
know whether all 64 bit CPUs support atomic operations on 32 bit
entities (for the reference count).
Something might be said for "compatibility" towards 32 bit
implementations that the maximum length is the same, but I don't really
have an opinion on whether this is actually a good idea (limiting the
size for compatibility reason).
At least Intel and PowerPC do have atomic operations on smaller sizes.
Intel: system programming guide vol 3 section 8.1.1 says byte, word,
doubleword, quadword (since Pentium) are all atomic if they are
naturally aligned. (word = 16 bits) 8.1.2.2 notes that LOCK is also best
to be used on naturally aligned boundaries for 8/16/32/64 bit accesses
for best performance.
PowerPC: pem64, 2005mar, section 5.1.2 says byte, halfword, word,
doubleword (64 bit only) are atomic if they are naturally aligned. (word
= 32 bits). lwarx/stwcx still exists on 64 bit implementations.
So both guarantee smaller reads/writes are atomic.
Micha
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