Product : ISaGRAF 3

Date    : 17-October-2000

File    : Difference between semaphore and Mutex.htm

Subject : Comparison between binary semaphores and mutex semaphores

Keywords: semaphore - mutex - porting - system layer


Comparison between Mutex and binary semaphores in ISaGRAF:

- Both have just 2 states (taken or free)

- Priority inheritance: with Mutex, a task (process) with low priority (T1) inherits the priority

of a higher priority task (T2) that is waiting for the same mutex. So the low priority task (T1) becomes a high priority task.

Now if a medium priority task needs to run, in fact it does not run, because T1 has a higher priority (until T1 has released the mutex, and T2 has finished its execution).

This is generally called "priority inversion safety".


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