Le 9 déc. 2011 à 10:36, Jean-Daniel Dupas a écrit : > > Le 9 déc. 2011 à 08:47, Ken Thomases a écrit : > >> On Dec 9, 2011, at 1:11 AM, Uli Kusterer wrote: >> >>> On 09.12.2011, at 07:55, Ken Thomases wrote: >>>> >>>> Double-checked locking is broken. It is an anti-pattern in many >>>> languages, including the C family under most common implementations. >>>> Don't use it. Google it if you want to confirm. One reference: >>>> <http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html>. >>> >>> Is this an issue that just exists when you want to write against ANSI C, or >>> is this an actual, practical concern when writing on the Mac, for MacOS or >>> iOS? >> >> It is an actual, practical concern. The compilers can re-order memory >> accesses. The CPU can, too. >> >> The second and subsequent threads through the double-checked lock can see >> the singleton pointer as non-nil, but the pointed-to object may not be >> valid. Its content may not have been written to memory, yet. >> > > It was a real concern on PPC, but on Intel platform AFAIK.
I mean but NOT on Intel plateform. > Memory barriers are noop on x86, as it does not perform out of order > execution of memory operations. > > http://locklessinc.com/articles/singleton_pattern/ > > That said,avoiding this pattern in the future may be a good thing. > > -- Jean-Daniel > > > > > _______________________________________________ > > Cocoa-dev mailing list ([email protected]) > > Please do not post admin requests or moderator comments to the list. > Contact the moderators at cocoa-dev-admins(at)lists.apple.com > > Help/Unsubscribe/Update your Subscription: > http://lists.apple.com/mailman/options/cocoa-dev/devlists%40shadowlab.org > > This email sent to [email protected] -- Jean-Daniel _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
