Date: Tue, 31 Oct 2000 11:23:16 -0800 (PST) From: Frank Mayhar <frank@exit.com> To: John Baldwin <jhb@FreeBSD.ORG> Cc: Cedric Berger <cedric@wireless-networks.com>, freebsd-smp@FreeBSD.ORG, Robert Watson <rwatson@FreeBSD.ORG> Subject: Re: Reference count invariants in a fine-grained threaded enviro Message-ID: <200010311923.e9VJNG309763@realtime.exit.com> In-Reply-To: <XFMail.001031111514.jhb@FreeBSD.org> from John Baldwin at "Oct 31, 2000 11:15:14 am"
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John Baldwin wrote: > They don't. The ia64 has a 'fetchadd' instruction, but x86 and alpha don't > have instructions for this, AFAIK. You can implement it using the > atomic_cmpset() functions however. Of course, what happens if you decrement > a reference and while you are freeing the object someone else obtains a > reference to it? Granted, this shouldn't be possible since if no one can > get to an object, no one should be able to find the object to allocate a > reference to it.... This kind of thing is indeed the gotcha. It takes thinking the problem out well and careful coding to avoid. Of course, avoiding a lock where possible is almost always a win. -- Frank Mayhar frank@exit.com http://www.exit.com/ Exit Consulting http://store.exit.com/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message
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