Re: AOO plugin for PD on SGI Irix

Thanks for checking!

> So I wrote a test that does an exclusive write lock/unlock and a couple of concurrent shared reader locks, it worked when just run without repetition. When repeating it a thousand times, I started to see once in a while when it seemingly randomly missed to get a reader lock.
I'm not sure I understand your test case. When you grab an exclusive 
lock, it is expected that you can't get a shared lock concurrently. What 
you should do instead is repeatedly obtaining short reader try-locks 
from several threads and see if any of them fail.

If that test still fails, it confirms our shared suspicion that it is a 
bug in the MIPS pthread implementation. (I'm pretty sure 
std::shared_mutext just uses pthread_rw_lock under the hood. If you have 
time, you can try to verify that.)

Christof

On 7/21/2026 12:28 AM, Wolfgang Gaggl via Pd-list wrote:
> I checked, AOO_HAVE_PTHREAD_RWLOCK is set true.
> I also intentionally failed this test to get mutex implementation, same behavior (maybe a bit worse in performance).
>
> So I wrote a test that does an exclusive write lock/unlock and a couple of concurrent shared reader locks, it worked when just run without repetition. When repeating it a thousand times, I started to see once in a while when it seemingly randomly missed to get a reader lock.
>
> This looks like a bug in the newer GCC pthread implementation for legacy MIPS (needed for C++11/17).
> Atomics and locks work with the native MIPSpro compiler, which however can only do C99/C++98.
>
> The workaround above works because if it misses that shared lock once in many executions only, a repeat try catches it without adding much computational overhead.
>
> Maybe I find a better solution at some point, or some platform specific compiler flag optimization that improve/fix it.
>
> Thanks for your debug suggestions!
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