Spin Locks Versus Semaphores

Knowing when to use a spin lock versus a semaphore is important to writing optimal code. In many cases, however, there is little choice. Only a spin lock can be used in interrupt context, whereas only a semaphore can be held while a task sleeps. Table 9.6 reviews the requirements that dictate which lock to use.

Table 9.6. What to Use: Spin Locks Versus Semaphores

Requirement	Recommended Lock
Low overhead locking	Spin lock is preferred
Short lock hold time	Spin lock is preferred
Long lock hold time	Semaphore is preferred
Need to lock from interrupt context	Spin lock is required
Need to sleep while holding lock	Semaphore is required