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. Regards, Ken _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) 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 arch...@mail-archive.com
