On Wed, Jan 6, 2010 at 3:09 PM, Sean Kelly <span dir="ltr"><<a href="mailto:kelly.sean@apple.com">kelly.sean@apple.com</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="im">On Jan 6, 2010, at 11:52 AM, Sean Kelly wrote:<br>
><br>
> In cases 1 and 2, all we really need to worry about is the assignment to x. On recent x86 we should be able to use 8 byte CAS to do it in one shot, but on other architectures the algorithm seems more complicated. I'd need to poke around to see if there's a published algorithm for updating two values together, but here's a shot at it that uses a special value assigned to the array pointer as a sentinel<br>
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</div>I just thought of a better approach. Simply set the '1' bit of the pointer to indicate that an update is taking place, since it really will never be set under normal circumstances.<br>
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</div></div></blockquote></div><br>But be sure to tell the GC that pointers can now look like (ptr % 4 == 1) as well as (ptr % 4 == 0). Otherwise a conservative GC might toss your object.<br><br>Kevin<br><br>