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Operating Systems Cheat Sheet

Common definitions and terminology in operating systems.

For Linux specifics, see the Linux Cheat Sheet.

Index

1. Lock
2. Mutex
3. Semaphore
4. Spin Lock

Lock

• Binary State: A lock is either locked or unlocked
• Blocking: If a thread attempts to acquire a lock already held by another thread, it is usually blocked until the lock is released.

Mutex

It’s a type of lock. Stands for mutually exclusive lock.

When a thread tries to acquire a already locked Mutex, the kernel puts that thread to sleep and it will be awakened once the lock is unlocked.

Semaphore

A semaphore is a more generalized version of a lock because it supports up to N threads to “enter” on a exclusive region.

If N = 1, it behaves like a lock, albeit an expensive one.

Spin Lock

It’s a type of lock that keeps trying to acquire a lock in a loop. It doesn’t require the thread to be context-switched, but consumes CPU cycles.