Friday, February 19, 2010

Mutex v/s Semaphore v/s Spinlock


- All are used for synchronization


Mutex provides one person to access a resource at a time, others must wait in a queue. Once person is done, the guy next in the queue acquire the resource.
So access is serial, one guy after other.

Semaphore provides more than one(up to N) guys to access N resources. So it gives you parallel access to a resource.

Spinlock is an aggressive mutex. In mutex, if you find that resource is locked by someone else, you (the thread/process) switch the context and start to wait(non-blocking).
Whereas spinlocks do not switch context and as soon as resource is free, they go and grab it. In this process of spinning, they consume many CPU cycles. Also, on a uni-processor machine they are useless and perform very badly (do I need to explain that?).

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