4 replies to this topic

[MadFrenchie]

Hi everyone,

Have a couple of questions here regarding the semaphores:

The semaphore invariant is often given as nW < nS + init.
How could we explain each term in this invariant? and How is the invariant enforced within the semaphore object?

And I'd like to know why might a semaphore be initialised to values: (a) 0, (b) 1, © N, where n > 1.


Any help would be grandly appreciated.
Thanks a bunch.

[MadFrenchie]

Bump.

Sorry to bump here but seriously need help here because of a major exam comming up quite soon !
Thanks a lot for any help

[WingedPanther]

You've given us no idea what the context of your question is. There are semaphores in data exchanges between systems, semaphores in threading, etc. Also, certain languages have the concept of semaphores as special meanings.

[MadFrenchie]

Sorry.
Meant Semaphores in Threading / Processes management.

Thanks for any further answer !

[WingedPanther]

Unfortunately, the discussion of semaphores may not be as standardized as you'd like to think. nW and nS don't have an inherent meaning. Doing a quick search, I found discussions of semaphores that refer to nP and nV, for example.

Always start with definitions. Also, think about the purpose of initializing a semaphore in the first place.