OpenSolaris adaptive mutexes: rationale and implementation optimization

OpenSolaris Adaptive Mutexes

OpenSolaris is an open-source operating system based on the Solaris operating system. It was created by Sun Microsystems and released in 2005. One of the key features of OpenSolaris is its use of adaptive mutexes.

What are adaptive mutexes?

A mutex, short for mutual exclusion, is a programming concept used to prevent multiple threads of execution from accessing a shared resource simultaneously. An adaptive mutex is a type of mutex that can dynamically adjust its behavior based on the state of the system. In other words, an adaptive mutex can change its behavior depending on whether the resource is contended or uncontended.

How do adaptive mutexes work in OpenSolaris?

Adaptive mutexes in OpenSolaris are implemented using a priority inheritance protocol. When a thread attempts to acquire an adaptive mutex and finds it already locked, it will block and the priority of the blocking thread will be raised to the same level as the thread holding the lock. This prevents the thread holding the lock from being preempted by lower priority threads, which could cause priority inversion and deadlock.

When the mutex is released, the priority of the blocked thread is lowered back to its original level. If multiple threads are blocked on the mutex, the priority of the highest priority thread is raised to the level of the thread holding the lock.

Adaptive mutexes in OpenSolaris also support recursive locking, which means that a thread can acquire the same mutex multiple times without deadlocking.

Advantages of adaptive mutexes

Adaptive mutexes have several advantages over other types of mutexes:

• Adaptive mutexes can reduce contention for shared resources, improving performance.
• Adaptive mutexes can dynamically adjust their behavior to prevent priority inversion and deadlock.
• Adaptive mutexes can support recursive locking, which can simplify code and reduce the risk of deadlocks.

Conclusion

Adaptive mutexes are an important feature of OpenSolaris, providing a flexible and efficient way to manage shared resources in a multi-threaded environment. By dynamically adjusting their behavior based on system conditions, adaptive mutexes can help prevent priority inversion, reduce contention for shared resources, and improve overall system performance.