Synchronization primitives

Spin

Spin is simply a spinlock, the most basic synchronization primitive. A spinlock is acquired by atomically setting its value. Other contexts trying to lock it in the meantime will loop until the value is clear (by unlocking it).

A spinlock does not have context ordering, nor make a process sleep. For this, use a Mutex.

RwLock

RwLock is a read-write lock (also called “pushlock”). It allows locking a resource like a spinlock, except it can accept several readers OR a single writer at once (contrary to the spinlock which accepts only one reader or writer at once).

This is useful to reduce contention when a resource is read often, but rarely written.

Wait queues

The WaitQueue makes a process wait on a resource by putting it in an interruptible sleep state. Processes are ordered in the queue in a FIFO fashion.

A process can wait on a resource until a given condition is fulfilled.

Mutex

A Mutex uses both a Spin and a WaitQueue. It allows locking a resources, putting processes waiting on it to sleep.

Unlocking the mutex wakes the next process in queue.