Hi, I did this change some time ago, but thought it's still worth sharing (better late than never!):
https://go-review.googlesource.com/c/go/+/34310/ https://go-review.googlesource.com/c/go/+/34310/8/src/sync/mutex.go There are mutexes that let threads in in strict FIFO order. This is good for fairness, but very bad for performance as 2 threads effectively need to go in lock-step: one thread can't immediate reacquire the mutex if there is another thread waiting, so it has to yield to the other thread, and then they swap roles and the second thread needs to yield to the first one and so on. There are also mutexes that allow the first thread that is _runnning_ when the mutex is free to acquire it. This is great for performance, but bad for fairness. In the worst case scenario, a thread holds a mutex for along time, then briefly releases and reacquires again. This can starve other threads literally infinitely: whenever they wake the first thread has already reacquired the mutex. The idea of the change to get best of both worlds: good fast path performance and (at eventual, or bounded) fairness. If a thread discovers that it is starved for too long (say a second), it marks the mutex state as "starved". In this mode Unlock will directly handoff mutex ownership to the blocked/started thread. When a thread discovers that it's not starving on lock operation but the mutex is in starvation mode, it resets the starvation flag the mutex returns to normal "no handoff" operation. This allowed to resolve unbounded starvation problems encountered in real applications with no performance effect for normal use cases. -- --- You received this message because you are subscribed to the Google Groups "Scalable Synchronization Algorithms" group. To unsubscribe from this group and stop receiving emails from it, send an email to lock-free+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/lock-free/CAEeQi3uJa82Lqws_MRATbZ_Jh1xBzoEO06FWP60OTiUBOMdfkQ%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
