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Asked: 2026-06-18T08:17:24+00:00

I had a question about reader/writer threads and I didn’t want to over-complicate things

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I had a question about reader/writer threads and I didn’t want to over-complicate things so I came here for some advice.

I have an array that will ultimately be read by 4 threads and written to by 3. (1 reader 3 read/write). My goal was to somehow not have any read operation block another thread while having any write operation block all threads until finished. I’m pretty sure I know how to do this with one semaphore per thread but is there any way to accomplish this with just one binary, counting, or mutex semaphore (or something less than 1 semaphore per thread). I will be using the VxWorks semaphore library.

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  1. Editorial Team

    Unless VxWorks supports some kind of shared/rwlock like the POSIX one, I am afraid it is going to be a bit more complicated than just simple.

    I would suggest using POSIX pthread_rwlock_t, if you have it. If you don’t and VxWorks does not offer any equivalent alternative, you will have to build one using other primitives. It is possible to build a rwlock on top of 2 semaphores and 3 mutexes and two integer variables. See Concurrent Control with “Readers” and “Writers”; P.J. Courtois, F. Heymans, and D.L. Parnas; MBLE Research Laboratory; Brussels, Belgium.

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