Darren Hart, IBM

Glibc 2.5 and later provide some support for priority inheritance (PI), but some gaps in the pthread_cond* APIs severely cripple its utility and lead to unexpected priority inversions and unpredictable thread wake-up patterns.

By adding kernel support for proxy locking of rt-mutexes and requeueing of tasks to PI-futexes, glibc can now provide PI support across the entire spectrum of mutex and condvar APIs.  This provides for more robust POSIX threading for very complex applications in which completely avoiding a priority inversion is impractical, if not impossible. Broadcast wakeups can now be more efficient, waking threads up in priority order as the contended resource becomes available.