So can we say that a mutex is a binary semaphore.
On Thu, Jun 10, 2010 at 11:26 PM, souravsain <[email protected]> wrote:
>
> Originally semaphore is a concept given by Dijkstra who says it is
> something that can have two operations P and V both atomic. In an OS
> (for example Unix) we have kernal objects called "semaphore" which
> have the same two atomic oprerations. It is used to control
> communication between 2 things (it can be 2 thread, 2 processes) as
> you have rightly mentioned. You can 'wait' for a semaphore. Someone
> else (thread/process) can broadcast a message that it has freed a
> semaphore. So emphasis is on communication.
>
> Mutex is more for controlling access to some resource. I do not know
> how many threads will access an object, say a linked list. What I only
> know is that the linked list should not be manipulated simultaneously
> by 2 or more threads. So my focus is on makeing sure than the shared
> object 'linked list' is in good shape. So a Mutex is in itself an
> object which sort of guards the resoure. So the mutex says If a thread
> wants to access / change the linked list, first lock me, then do ur
> changes and unlock me.
>
> Having said this, Binary semaphore is one which can change value
> between 2 states (enerally 1 and 0) and most interestingly, we
> implement a mutex object by having a binary semaphore inside the Mutex
> object.
>
> class Mutex
> {
> private BinSem MySem;
> lock()
> {
> if MySem is 0 then lock or wait
> }
> unlock()
> {
> if MySem is 1 broadcast all am releasing and release.
> }
> }
>
>
> On Jun 10, 8:56 pm, sharad kumar <[email protected]> wrote:
> > @sharad but when it is binary semaphore then only one process is
> accessing
> > the resource,rest all are blocked....which means that only that process
> who
> > locked bin. sem will unlock it .....plzzz correct me if i m wrong
>
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--
Regards,
Rishi B. Agrawal
http://www.linkedin.com/in/rishibagrawal
http://code.google.com/p/fscops/
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