What is the real difference Conceptually and Implementation point of view between
Semophore, Mutex, Monitor?
We say Semophores are resource allocation counter... OK I understand this..
For Mutex we say mutex are Binary Semophore... Gosh what's that???
Monitor guards the entry point for an objects... i.e. only one thread can acquire it and can run one of it's guarded entry points??? Then what are mutex for??
Semaphores are a locking mechanism, iirc they can conceptually be configured to allow multiple aceess to an object; e.g. Access three at a time, four at a time, etc.
Mutex are a special case of a semaphore for ensuring mutual exclusion, I.e. only one can access the protected resource at any given time.
It is important to note that neither the semaphore nor mutex ensure strict ordering when waiting for access to the shared resource. When the resource becomes accessible some waiting thread will gain access but no garuantees are made about which thread that will be. Statistically, eventually all threads will (must) gain access.
A monitor enforces a precedence on the waiting threads/processes by queueing them in a particular order, not necessarily how they arrive. An operating system is an example of a monitor - ensuring a single process has the CPU at any given time.