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Editorial Team
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Asked: 2026-06-02T12:07:17+00:00

My application makes heavy use of GCD, and almost everything is split up in

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My application makes heavy use of GCD, and almost everything is split up in small tasks handled by dispatches. However, the underlying data model is mostly read and only occasionally written.

I currently use locks to prevent changes to the critical data structures while reading. But after looking into locks some more today, I found NSConditionLock and some page about read-write locks. The latter is exactly what I need.

I found this implementation: http://cocoaheads.byu.edu/wiki/locks . My question is, will this implementation work with GCD, seeing that it uses PThreads?

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  1. Editorial Team

    It will still work. pthreads is the threading API which underlies all of the other thread-using APIs on Mac OS X. (Under that there’s Mach thread activations, but that’s SPI, not API.) Anyway, the pthreads locks don’t really require that you use pthreads threads.

    However, GCD offers a better alternative as of iOS 5: dispatch_barrier_async(). Basically, you have a private concurrent queue. You submit all read operations to it in the normal fashion. You submit write operations to it using the barrier routines. Ta-da! Read-write locking.

    You can learn more about this if you have access to the WWDC 2011 session video for Session 210 – Mastering Grand Central Dispatch.

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