Hey guys, A semaphore is an extension of a mutex. A mutex allows one thread inside the critical section, a semaphore allows n threads in a critical section (when the number n is given as a parameter on the initialization). A semaphore is useful when a resource has more than one instance, and a mutex can be implemented by initializing a semaphore with the value 1.
Thanks Ankit On Sat, Jun 18, 2011 at 2:04 AM, Dumanshu <duman...@gmail.com> wrote: > @DK: So u mean to say that Mutex and binary semaphores provide > completely same functionality. Right? > Say u have a resource R and u can provide access to this particular > only one at a time (lets say multiple threads are there). > Now we can use mutex. One by one the threads will lock it and will use > the resource and then unlock it for other threads. > We can use binary semaphore. One thread will signal it, value will be > 0 and use the resource. Later, it will signal it to value 1 so now > other thread can do the same thing. > > So here we dont have any difference between mutex and binary > semaphore. We can use either. > > Now plz give me some examples where mutex is preferred over binary > semaphore and vice-versa. > > Thanks > Dumanshu > > On Jun 18, 1:58 am, DK <divyekap...@gmail.com> wrote: >> @Dumanshu/@Ankit: Of course mutexes can be made to work between processes >> (it's an implementation detail). But the *concept* of a mutex is Owner + >> (Lock & Key) pair. By adding the concept of Owner to a lock, we can ensure >> that only the person who locked the lock can open it. This *guarantees* >> mutual exclusion (which is unlike a semaphore). A semaphore is a signalling >> mechanism between threads/processes that simply indicates an event that has >> occured asynchronously to the process/thread's flow of control (for >> processes/threads other than the event generating process of-course). It is >> often used to indicate that cooperative progress may be possible on >> resources under contention or synchronization between states may be >> required. Any cooperating process/thread can modify the value of a semaphore >> which is not true of a mutex. >> >> Note: Mutex and Semaphore are essentially concepts. Their implementations >> can vary in different systems and have different implementation constraints >> but the theory is clear. The two are different and serve different purposes >> though they may share implementation details. >> >> -- >> DK >> >> http://twitter.com/divyekapoorhttp://www.divye.in > > -- > You received this message because you are subscribed to the Google Groups > "Algorithm Geeks" group. > To post to this group, send email to algogeeks@googlegroups.com. > To unsubscribe from this group, send email to > algogeeks+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/algogeeks?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Algorithm Geeks" group. To post to this group, send email to algogeeks@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
