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
--
You received this message because you are subscribed to the Google Groups
"Algorithm Geeks" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/algogeeks?hl=en.
